The Immune System Overview
106 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which of the following are types of active humoral immunity?

  • Naturally acquired (correct)
  • Artificially acquired (correct)
  • Passive acquired
  • Recessive acquired

    • IgM is the first immunoglobulin class secreted during the primary immune response.

    True

    What are antibodies also known as?

    Immunoglobulins

    Match the immunoglobulin classes with their characteristics:

    <p>IgG = Most abundant in plasma, crosses placenta IgA = Found in secretions, helps prevent pathogen entry IgM = First antibody released during primary response IgE = Involved in allergic reactions and parasitic infections IgD = Functions as B cell receptor</p> Signup and view all the answers

    The main antibody of both secondary and late primary responses is ___

    <p>IgG</p> Signup and view all the answers

    What role do MHC proteins play in T cell function?

    <p>Antigen presentation</p> Signup and view all the answers

    Class I MHC proteins are found on all body cells except red blood cells.

    <p>True</p> Signup and view all the answers

    Which of the following is NOT a defensive mechanism used by antibodies?

    <p>Enhancement</p> Signup and view all the answers

    What is the characteristic shape of an antibody molecule?

    <p>Y-shaped</p> Signup and view all the answers

    Which cells display Class I MHC proteins?

    <p>All nucleated cells</p> Signup and view all the answers

    Which of the following is recognized by Naive CD8 cells?

    <p>Endogenous antigens</p> Signup and view all the answers

    CD4 cells can recognize antigens only on Class II MHC proteins.

    <p>True</p> Signup and view all the answers

    What must T cells bind to in order to be activated?

    <p>Co-stimulatory signals</p> Signup and view all the answers

    What is the role of cytokines in T cell activation?

    <p>They facilitate T cell differentiation</p> Signup and view all the answers

    What types of cells can Helper T cells activate?

    <p>B and other T cells</p> Signup and view all the answers

    Cytotoxic T cells directly attack and kill _______.

    <p>virus-infected cells</p> Signup and view all the answers

    Regulatory T cells enhance immune response.

    <p>False</p> Signup and view all the answers

    Which cytokine enhances the killing power of macrophages?

    <p>Gamma interferon</p> Signup and view all the answers

    What is MHC restriction?

    <p>Different antigen presentation requirements for CD4 and CD8 cells.</p> Signup and view all the answers

    Which cells detect cancerous cells?

    <p>Cytotoxic T cells</p> Signup and view all the answers

    What are the three lines of defense of the immune system?

    <p>Surface barriers, innate internal defenses, adaptive (specific) defense system</p> Signup and view all the answers

    What is the primary function of surface barriers in the immune system?

    <p>To provide a mechanical barrier</p> Signup and view all the answers

    Which of the following are protective mechanisms associated with intact skin epidermis?

    <p>All of the above</p> Signup and view all the answers

    Innate internal defenses are the first line of defense in the immune system.

    <p>False</p> Signup and view all the answers

    What role do Toll-like receptors (TLRs) play in the immune system?

    <p>They trigger immune responses by recognizing specific shapes of pathogens.</p> Signup and view all the answers

    What type of cell is primarily responsible for phagocytosis?

    <p>Phagocytes</p> Signup and view all the answers

    Neutrophils can undergo netosis to trap pathogens.

    <p>True</p> Signup and view all the answers

    The _______ is a process where pathogens are coated with opsonins.

    <p>opsonization</p> Signup and view all the answers

    What are the four cardinal signs of acute inflammation?

    <p>Redness, heat, swelling, and pain</p> Signup and view all the answers

    What is one of the physiological effects of histamine during an inflammatory response?

    <p>Promote vasodilation</p> Signup and view all the answers

    What is the function of a CD8 T cell?

    <p>Kills invaded body cells and cancer cells.</p> Signup and view all the answers

    What transformation do monocytes undergo after about 12 hours in tissue?

    <p>Transform into macrophages</p> Signup and view all the answers

    What role do regulatory T cells play in the immune system?

    <p>They slow or stop the activity of the immune system.</p> Signup and view all the answers

    What is a memory cell?

    <p>A descendant of activated B or T cells that remains in the body for years.</p> Signup and view all the answers

    What is the primary role of an antigen-presenting cell (APC)?

    <p>To engulf and digest antigens and present parts on its plasma membrane.</p> Signup and view all the answers

    What is an antigen?

    <p>A substance capable of provoking an immune response.</p> Signup and view all the answers

    What do antibodies do?

    <p>Attach to antigens and can cause complement activation or mark them for destruction.</p> Signup and view all the answers

    What effect do perforins and granzymes have?

    <p>Perforins create pores in target cells, while granzymes induce apoptosis.</p> Signup and view all the answers

    What is the incidence of autoimmune diseases in North America?

    <p>Approximately 5% of adults are affected.</p> Signup and view all the answers

    What are common treatments for autoimmune diseases?

    <p>Corticosteroids and treatments targeting specific immune responses.</p> Signup and view all the answers

    The immune system stem cells primarily develop in the bone marrow throughout a person's life.

    <p>False</p> Signup and view all the answers

    How does aging affect the immune system?

    <p>Efficiency wanes and the ability to fight infections declines.</p> Signup and view all the answers

    What factor is needed for the activation of CD8 T cells?

    <p>Vitamin D.</p> Signup and view all the answers

    What are the main functions of antimicrobial proteins?

    <p>Attacking microbes directly</p> Signup and view all the answers

    What are the most important antimicrobial proteins?

    <p>Interferons and complement proteins</p> Signup and view all the answers

    Which of the following is a characteristic of interferons?

    <p>They can block viral replication</p> Signup and view all the answers

    What types of cells secrete interferons?

    <p>Virus-infected cells</p> Signup and view all the answers

    What are the three pathways that activate the complement system?

    <p>Lectin pathway</p> Signup and view all the answers

    Fever is caused by antibodies binding to pathogens.

    <p>False</p> Signup and view all the answers

    What is the role of pyrogens in fever?

    <p>To raise body temperature</p> Signup and view all the answers

    What type of immunity is provided by B lymphocytes?

    <p>Humoral immunity</p> Signup and view all the answers

    What are antigens?

    <p>Substances that provoke an immune response</p> Signup and view all the answers

    Match the cells with their roles in the immune response:

    <p>B lymphocytes = Provide humoral immunity T lymphocytes = Provide cellular immunity Antigen-presenting cells = Present antigens to T cells</p> Signup and view all the answers

    What happens to naive B cells upon activation?

    <p>They proliferate and differentiate into plasma cells</p> Signup and view all the answers

    The adaptive immune system is fast to mobilize compared to the innate immune system.

    <p>False</p> Signup and view all the answers

    What provides the first line of defense in the immune system?

    <p>Surface barriers</p> Signup and view all the answers

    What are the three lines of defense of the immune system?

    <p>All of the above</p> Signup and view all the answers

    What is the role of phagocytes in the immune response?

    <p>To ingest and digest foreign invaders and cellular debris</p> Signup and view all the answers

    The adaptive immune system is immediately activated upon pathogen entry.

    <p>False</p> Signup and view all the answers

    Match the following surface barriers with their functions:

    <p>Intact skin epidermis = Forms a mechanical barrier Acid mantle of skin = Inhibits bacterial growth Mucus = Traps microorganisms Cilia = Moves debris-laden mucus</p> Signup and view all the answers

    What role do natural killer (NK) cells play in the immune system?

    <p>They kill cancer and virus-infected cells.</p> Signup and view all the answers

    Inflammation is a specific response to a particular pathogen.

    <p>False</p> Signup and view all the answers

    What are the four cardinal signs of acute inflammation?

    <p>All of the above</p> Signup and view all the answers

    What is opsonization?

    <p>Coating pathogens with opsonins to enhance phagocytosis.</p> Signup and view all the answers

    The larger granular lymphocytes that police blood and lymph are known as ______.

    <p>natural killer (NK) cells</p> Signup and view all the answers

    What is the function of an effector CD8 T cell?

    <p>Kills invaded body cells and cancer cells.</p> Signup and view all the answers

    What type of T cell slows or stops the activity of the immune system?

    <p>Regulatory T cell (TReg).</p> Signup and view all the answers

    What is a memory cell?

    <p>A descendant of activated B cells or activated T cells that responds quickly to subsequent encounters with the same antigen.</p> Signup and view all the answers

    What is an antigen-presenting cell?

    <p>Any of several cell types that engulfs and digests antigens and presents parts of them on its plasma membrane for recognition by T cells.</p> Signup and view all the answers

    What is the function of antibodies in the immune response?

    <p>Proteins produced by B cells that mark antigens for destruction by phagocytes.</p> Signup and view all the answers

    What are common examples of autoimmune diseases?

    <p>Multiple sclerosis</p> Signup and view all the answers

    What are the treatments for autoimmune diseases?

    <p>Treatments typically suppress the immune system or target specific aspects of the immune response.</p> Signup and view all the answers

    What factors can influence immune function?

    <p>Nervous system health and diet.</p> Signup and view all the answers

    The thymus becomes more active with age.

    <p>False</p> Signup and view all the answers

    What happens to the immune system efficiency with age?

    <p>It wanes, and the ability to fight infections declines.</p> Signup and view all the answers

    What are the two main functions of antimicrobial proteins?

    <p>Hindering their ability to reproduce</p> Signup and view all the answers

    What are the most important antimicrobial proteins?

    <p>Interferons and complement proteins</p> Signup and view all the answers

    What is the role of interferons?

    <p>They inhibit viral replication and activate immune cells.</p> Signup and view all the answers

    What is the function of the complement system?

    <p>Lyses microorganisms</p> Signup and view all the answers

    Fever enhances the ability of T lymphocytes to migrate into lymph nodes.

    <p>True</p> Signup and view all the answers

    What are antigens?

    <p>Substances that trigger the body's adaptive defenses.</p> Signup and view all the answers

    T cells undergo education in the ______.

    <p>thymus</p> Signup and view all the answers

    What type of immunity do T lymphocytes provide?

    <p>Cell-mediated immunity</p> Signup and view all the answers

    B cells secrete antibodies.

    <p>True</p> Signup and view all the answers

    What is clonal selection?

    <p>The process of activating specific B or T cells in response to an antigen.</p> Signup and view all the answers

    Match the type of lymphocyte to its function:

    <p>B lymphocytes = Humoral immunity T lymphocytes = Cellular immunity Helper T cells = Coordinate immune response Cytotoxic T cells = Kill infected cells</p> Signup and view all the answers

    What are the two types of active humoral immunity?

    <p>Both A and B</p> Signup and view all the answers

    What is the role of vaccines in active humoral immunity?

    <p>They provide antigenic determinants that are immunogenic and reactive.</p> Signup and view all the answers

    Which immunoglobulin class is most abundant in plasma?

    <p>IgG</p> Signup and view all the answers

    IgE antibodies are secreted in response to parasitic infections and allergic reactions.

    <p>True</p> Signup and view all the answers

    What does the acronym GAMED help remember?

    <p>The five classes of immunoglobulins: IgG, IgA, IgM, IgE, and IgD.</p> Signup and view all the answers

    Which class of MHC proteins is found on the surface of virtually all body cells except RBCs?

    <p>Class I</p> Signup and view all the answers

    What are the main effector cells that CD4 and CD8 T cells can differentiate into?

    <p>Helper T cells (TH) and Cytotoxic T cells (TC).</p> Signup and view all the answers

    The first antibody released during a primary immune response is ___ .

    <p>IgM</p> Signup and view all the answers

    Antibodies can destroy antigens directly.

    <p>False</p> Signup and view all the answers

    Match the following antibody classes with their characteristics:

    <p>IgG = Most abundant in plasma, confers passive immunity IgA = Found in secretions, helps prevent pathogen entry IgM = First antibody released during primary response IgE = Involved in allergic reactions and parasitic infections</p> Signup and view all the answers

    Which class of MHC proteins is displayed by all nucleated cells?

    <p>Class I</p> Signup and view all the answers

    Which cells are recognized by Class II MHC proteins?

    <p>B cells</p> Signup and view all the answers

    CD4 cells are restricted to binding antigens only on Class II proteins.

    <p>True</p> Signup and view all the answers

    CD8 cells are activated by Class II MHC proteins.

    <p>False</p> Signup and view all the answers

    What is required for T cell activation?

    <p>Antigen binding and co-stimulation</p> Signup and view all the answers

    What role do cytokines play in T cell response?

    <p>They influence cell development and amplify immune responses.</p> Signup and view all the answers

    Which type of T cell plays a central role in activating B cells?

    <p>Helper T cells</p> Signup and view all the answers

    Regulatory T cells help in enhancing the immune response.

    <p>False</p> Signup and view all the answers

    Activated T cells differentiate into either _____ or _____ cells.

    <p>memory, effector</p> Signup and view all the answers

    What are the two mechanisms used by cytotoxic T cells to kill target cells?

    <p>Release of perforins and granzymes, binding specific receptors.</p> Signup and view all the answers

    Study Notes

    The Immune System

    • The immune system provides resistance to disease-causing microorganisms like bacteria, fungi, and viruses.
    • The body has three lines of defense against pathogens.
    • The First line of defense is surface barriers such as skin and mucosae, which aim to stop invaders from entering.
    • The Second line of defense is innate internal defenses which are activated when the first line of defense is breached. This line relies on inflammation and internal defenses like antimicrobial proteins and phagocytes to inhibit the spread of invaders.
    • The Third line of defense is adaptive (specific) defense system, which is activated when the innate defenses cannot stop the invaders. This system takes longer to mount than the innate response.

    The Innate Defenses

    • Innate defenses reduce the workload for the adaptive system.

    Surface Barriers Act as the First Line of Defense

    • Surface barriers are the skin and mucous membranes along with their secretions.
    • The skin is heavily keratinized, making it effective against most microbes.
    • Mucosae provide similar mechanical barriers within the body.
    • Surface barriers produce protective chemicals to inhibit or destroy microbes.

    Innate Internal Defenses Are Cells and Chemicals That Act as the Second Line of Defense

    • The second line of defense includes various nonspecific cellular and chemical means to protect the body.
    • Some of the key defenses include phagocytes, natural killer cells, antimicrobial proteins, inflammation, and fever.
    • The innate defense identifies potential pathogens by recognizing specific molecules found on them, which are not found in normal human cells.
    • Cells have pattern recognition receptors to identify invaders. One class, Toll-like receptors (TLRs), play a central role in triggering immune responses.

    Phagocytes

    • Phagocytes are white blood cells (WBCs) that ingest and digest foreign invaders and cellular debris.
    • Neutrophils are the most abundant phagocytes; they phagocytize infectious material in tissues.
    • Macrophages are the most active phagocytes.
    • Free macrophages wander through tissue spaces, and fixed macrophages are permanent residents of particular organs.

    Phagocytosis

    • Phagocytosis starts when phagocyte receptors bind the particle. The particle is pulled inside and enclosed within a membrane-lined vesicle.
    • Phagosomes fuse with a lysosome to form a phagolysosome. This acidifies and then lysosomal enzymes digest the contents of the phagolysosome.
    • Some pathogens are resistant to the lysosomal enzymes.
    • Some microbes have external capsules that hide their surface carbohydrate signatures.
    • The immune system counters this by coating pathogens with opsonins, which act as "handles" for phagocytes to grab on to, greatly accelerating phagocytosis.

    Natural Killer (NK) Cells

    • Natural Killer (NK) Cells are large granular lymphocytes which police the blood and lymph.
    • NK cells identify general abnormalities instead of specific infected or tumor cells.
    • NK cells can kill cancer and virus-infected cells before the adaptive immune system is activated by inducing apoptosis.
    • NK cells also secrete potent chemicals that enhance the inflammatory response.

    Inflammation

    • Inflammation is a nonspecific response to any tissue injury.
    • The suffix “itis” signifies inflammation (e.g., tonsillitis, appendicitis, and tendonitis).
    • Inflammation helps prevent the spread of pathogens, dispose of cell debris and pathogens, alert the adaptive immune system, and sets the stage for repair.
    • The four cardinal signs of acute inflammation are: redness, heat, swelling, and pain.

    Antimicrobial Proteins

    • Antimicrobial proteins enhance innate defenses.
    • The most important antimicrobial proteins are interferons and complement proteins.

    Interferons

    • Interferons (IFNs) are a family of immune modulating proteins produced by various cells.
    • Virus-infected cells can secrete IFNs that “interfere” with viral replication in neighboring healthy cells by stimulating the production of proteins that block protein synthesis and degrade viral RNA.
    • IFN alpha ( ) and beta () also activate NK cells.
    • IFN gamma ( ) is secreted by lymphocytes and has widespread defense mobilizing effects, including activating macrophages.

    Complement System

    • The complement system consists of at least 20 plasma proteins that circulate in inactive state.

    The Complement System

    • The complement system is a group of ~20 bloodborne proteins that act together in a cascade to destroy pathogens.
    • It is activated by three different pathways:
      • The classical pathway, initiated by antibodies binding to a pathogen.
      • The lectin pathway relies on lectins (proteins produced by the innate immune system) binding to specific sugars on microbial surfaces.
      • The alternative pathway involves spontaneous activation of the complement cascade on microbial surfaces that lack inhibitors of complement activation.
    • The complement system contributes to:
      • Lysis of microbes
      • Enhancement of phagocytosis (opsonization)
      • Amplification of the inflammatory response

    Fever

    • Fever is a systemic response to invading microbes characterized by an increase in body temperature.
    • Leukocytes and macrophages exposed to foreign substances release pyrogens, which act on neurons in the hypothalamus to raise the body temperature.
    • Fever can enhance immune responses by:
      • Increasing T lymphocytes and monocytes migration to lymph nodes
      • Enhancing metabolic rate, accelerating repair and T lymphocyte production
      • Inhibiting bacterial growth by limiting access to iron

    Adaptive Immune Response

    • The adaptive immune system is the third line of defense, targeting and eliminating specific pathogens.
    • It functions distinct from innate defenses as it requires initial exposure to an antigen to become primed; this priming takes time.
    • The adaptive immune system consists of two arms:
      • Humoral immunity involves antibodies primarily targeting extracellular targets such as bacteria, bacterial toxins, and viruses.
      • Cellular immunity involves lymphocytes directly attacking infected cells, cancer cells, and foreign cells.

    Antigens

    • Antigens are substances that mobilize the adaptive defenses, causing an immune response.
    • They are the targets of all adaptive immune responses.
    • Most antigens are large, complex molecules foreign to the body and are recognized as non-self.

    Self-Antigens

    • Self-antigens are proteins present on all body cells, usually not antigenic to the individual, but strongly antigenic to others.
    • They are the cause for transfusion reactions and graft rejection.
    • They include MHC proteins, coded by the major histocompatibility complex (MHC) genes, unique to each person.
    • T lymphocytes only bind antigens presented on MHC proteins.

    Cells of the Adaptive Immune Response

    • Three crucial cell types are involved:
      • B lymphocytes (B cells) provide humoral immunity.
      • T lymphocytes (T cells) provide cellular immunity.
      • Antigen-presenting cells (APCs) present antigens to T cells.

    Lymphocyte Development and Activation

    • B and T lymphocytes originate from stem cells in the bone marrow.
    • B lymphocytes mature in the bone marrow; T lymphocytes mature in the thymus.
    • Lymphocytes undergo a selection process to ensure they recognize self-MHC proteins and do not attack self-antigens.
    • Once exposed to a specific antigen, they become activated and proliferate into effector cells or memory cells.

    Antigen-Presenting Cells (APCs)

    • APCs engulf antigens and present them to T cells.
    • Major APC types include:
      • Dendritic cells, highly effective antigen presenters, capturing antigens and migrating to lymph nodes to present them to T cells.
      • Macrophages, presenting antigens to T cells, maintaining their activation, and becoming activated macrophages themselves, engulfing pathogens and triggering inflammatory responses.
      • B lymphocytes present antigens to helper T cells to assist in their own activation.

    Antibodies

    • Antibodies, also known as immunoglobulins (Igs), are proteins secreted by plasma cells.
    • They bind specifically to antigens.
    • They are grouped into five classes: IgG, IgA, IgM, IgE, and IgD (GAMED).
    • IgG is the most abundant antibody in circulation, responsible for both secondary and late primary responses, and crosses the placenta.
    • IgA is found in secretions and helps prevent pathogen entry.
    • IgM is the first antibody released during a primary response.
    • IgE is involved in allergic reactions and binds to mast cells and basophils for histamine release.
    • IgD acts as a B cell surface receptor.

    Immunological Memory

    • Primary immune response is the initial exposure to an antigen, with a lag period for cell proliferation and differentiation.
    • Secondary immune response is the subsequent exposure to the same antigen, which is faster, more prolonged, and more effective, due to memory cells providing immunological memory.

    Active and Passive Humoral Immunity

    • Active humoral immunity results from B cells encountering and producing antibodies against antigens.
      • Naturally acquired immunity occurs via infection.
      • Artificially acquired immunity is the result of vaccination.
    • Passive humoral immunity occurs by receiving pre-made antibodies from another source.
      • Naturally acquired immunity through the placenta or breast milk.
      • Artificially acquired immunity by receiving antibody-containing serum.

    Immunoglobulin Classes

    • IgM is the first immunoglobulin class secreted by plasma cells during the primary response.

    • The presence of IgM in plasma usually indicates current infection by the pathogen eliciting IgM’s formation.

    • IgM readily activates complement.

    • IgM exists in monomer and pentamer forms. The monomer serves as an antigen receptor on the B cell surface. The pentamer circulates in blood.

    • IgM (pentamer) has numerous antigen-binding sites, making it a potent agglutinating agent.

    • IgA exists as a dimer, referred to as “secretory IgA,” found in body secretions such as saliva, sweat, intestinal juice, and milk.

    • Secretory IgA helps stop pathogens from attaching to epithelial cell surfaces like mucous membranes and the epidermis.

    • IgA monomer exists in limited amounts in plasma.

    • IgD is found on the B cell surface.

    • IgD functions as a B cell antigen receptor (as does IgM).

    • IgG is the most abundant antibody in plasma, accounting for 75–85% of circulating antibodies.

    • IgG is the main antibody of both secondary and late primary responses.

    • IgG readily activates complement.

    • IgG protects against bacteria, viruses, and toxins circulating in blood and lymph.

    • IgG crosses the placenta and confers passive immunity from the mother to the fetus.

    • IgE has a stem end that binds to mast cells or basophils.

    • Antigen binding to its receptor end triggers these cells to release histamine and other chemicals that mediate inflammation and an allergic reaction.

    • IgE is secreted by plasma cells in skin, mucosae of the gastrointestinal and respiratory tracts, and tonsils.

    • Only traces of IgE are found in plasma.

    • IgE levels rise during severe allergic attacks or chronic parasitic infections of the gastrointestinal tract.

    Antibodies

    • Plasma B cells can switch from making one class of antibodies to another while retaining specificity for the same antigen.

    • IgM is the first Ig released during the primary response. Later plasma cells begin to secrete IgG (also the primary Ig for all secondary responses).

    • Switching from IgM to IgA or IgE can also occur.

    • Antibodies cannot destroy antigens, instead, they inactivate and tag them for destruction by forming antigen-antibody (immune) complexes.

    • Defensive mechanisms used by antibodies include:

      • Neutralization: Antibodies block the binding sites of toxins or viruses to prevent them from causing harm.
      • Agglutination: Antibodies bind to multiple antigens, clumping them together. This makes it easier for phagocytes to engulf them.
      • Precipitation: Antibodies cross-link soluble antigens, forming an insoluble complex that precipitates out of the solution, where they can be eliminated by phagocytes.
      • Complement activation: Antibodies bind to antigens and activate the complement pathway, which leads to the lysis of the target cell.

    Clinical—Homeostatic Imbalance

    • Antibodies may be insufficient for infections by large parasitic worms like Ascaris and Schistosoma.
    • IgE antibodies still play a critical role in destroying worms by binding to their surface, marking them for destruction by eosinophils.
    • Eosinophils bind to exposed stems of IgE, triggering them to release toxic chemicals onto the worm, lysing it from the outside.

    Cellular Immunity

    • T cells provoke a cellular immune response when presented with antigens.
    • Some T cells directly kill cells infected by viruses or bacteria, cancerous or abnormal cells or foreign cells.
    • Other T cells release chemicals that regulate the immune response.

    Major T Cells Types

    • Two major T cell populations (CD4, CD8) are based on their cell differentiation glycoproteins.
    • Activated CD4 and CD8 cells differentiate into three major kinds of effector cells:
      • Most CD4 cells become helper T (TH) cells that help activate B cells, other T cells, and macrophages and direct adaptive immune response.
      • Some CD4 become regulatory T (TReg) cells that moderate the immune response.
      • Most CD8 cells become cytotoxic T cells (TC) capable of destroying infected and abnormal or foreign cells.
    • Activated CD4 and CD8 cells can also become memory T cells.

    MHC Proteins and Antigen Presentation

    • T cells can only respond to processed antigen fragments displayed on cells' surfaces by major histocompatibility complex (MHC) proteins, either class 1 or class II.

    • Antigen presentation is needed to activate naive T cells and ensure the normal functioning of effector T cells.

    • Class I MHC proteins are found on the surface of virtually all body cells except RBCs. They display endogenous antigens made inside the cell.

      • Healthy cells display pieces of normal body proteins (self-antigen).
      • Infected cells display parts of proteins that belong to the pathogen (antigen).
      • Cancer cells display pieces of abnormal proteins (antigen).

    • The role of class I MHC proteins is to activate naive CD8 cells and “inform” cytotoxic T cells that pathogens are hiding in body cells.

    • Class II MHC proteins are found only on the surfaces of cells that present antigens to CD4 cells such as dendritic cells, macrophages, and B cells.

    • Class II MHC proteins display exogenous antigens—antigens from outside the cell that have been engulfed by the cell displaying them.

      • The engulfed antigen is broken down by proteases inside the phagolysosome (into larger, 14–17 amino acid fragments).
      • Vesicles from the ER containing class II proteins fuse with the phagolysosome.
      • Fragments bind to the groove of the MHC protein before it's inserted onto the cell surface.

    • The role of class II MHC proteins is to activate naive CD4 cells, letting them know that “help” is required.

    MHC Restriction

    • CD4 and CD8 cells have different requirements for the MHC protein class that presents antigens to them.
      • CD4 is restricted to binding antigens only on class II proteins found on antigen-presenting cell (APC) surfaces.
      • CD8 is restricted to antigens bound to class I proteins found on all body cell surfaces (except RBCs), including APCs.
      • Once activated, cytotoxic T cells seek out the same antigen on class I MHC proteins on any cell.

    Activation and Differentiation of T Cells

    • T cells can be activated only by APCs through a two-step process involving both antigen binding and co-stimulation.

      • Both events must occur on the same APC and are required for clonal selection.

    • Antigen Binding: T cell antigen receptors (TCRs) bind to the antigen-MHC complex on the APC surface. This triggers intracellular signaling pathways that lead to T cell activation.

      • Other T cell surface proteins are involved in T cell activation (e.g., CD4 and CD8 proteins are adhesion molecules that help bind cells during antigen recognition).

    • Co-stimulation is also required for T cell activation. This means that the T cell must also bind to one or more co-stimulatory signals (molecules that appear on surfaces of APCs in damaged or infected tissues).

      • If co-stimulation doesn't occur, the T cell becomes unresponsive to the antigen (called anergy), a safeguard against unwanted T cell activation.

    The Complement System

    • The complement system is a group of bloodborne proteins that activate a cascade of reactions to lyse microorganisms and intensify inflammatory responses.
    • It is activated via three different pathways: the classical pathway involving antibodies, the lectin pathway involving lectins, and the alternative pathway involving spontaneous activation of complement cascades.

    Fever

    • Fever is a systemic response to invading microbes, raising the body's temperature above normal.
    • Fever is caused by pyrogens, chemicals released by leukocytes and macrophages, which act on neurons in the hypothalamus, the body's thermostat.
    • Fever has benefits for the immune response by: increasing migration of T lymphocytes and monocytes to lymph nodes, enhancing metabolic rate for tissue repair and T lymphocyte production, and suppressing bacterial growth by limiting access to metal ions.

    Innate Cellular and Chemical Defenses

    • Phagocytes, like macrophages and neutrophils, engulf and destroy pathogens.
    • Natural killer (NK) cells promote cell death by directly attacking virus-infected or cancerous cells, recognizing general abnormalities rather than specific antigens.
    • The inflammatory response limits the spread of injurious agents, disposes of pathogens and dead cells, and promotes tissue repair.
    • Interferons are antimicrobial proteins released by virus-infected cells and certain lymphocytes, protecting uninfected cells from viral takeover.

    Adaptive Defenses

    • The adaptive immune system is a specific defensive system that targets and eliminates pathogens.
    • Unlike innate defenses, the adaptive immune system requires prior exposure to an antigen to develop a response.
    • The adaptive immune system consists of humoral immunity (antibody-mediated) and cellular immunity (cell-mediated).

    Key Differences Between Adaptive and Innate Defenses

    • Adaptive defenses involve B and T lymphocytes while innate defenses involve diverse cells, processes, and structures.
    • Adaptive defenses are specific to antigens, while innate defenses are nonspecific.
    • Adaptive defenses are slow to mobilize, while innate defenses are fast and always ready.
    • Adaptive defenses have memory and react more strongly to subsequent exposures, while innate defenses usually lack memory.
    • Adaptive defenses are systemic (bodywide) while innate defenses are largely restricted to the site of initial infections.

    Antigens and the Adaptive Immune System

    • Antigens are substances that trigger the body's adaptive defenses and provoke an immune response.

    • Most antigens are complex molecules (natural or synthetic) that are foreign and not normally found in the body.

    • Antigens have multiple antigenic determinants (epitopes) that can bind to different antibodies.

      Self-Antigens and MHC Proteins

    • Self-antigens are proteins on body cell surfaces that are not antigenic to self but are strongly antigenic to others.

    • Self-antigens include major histocompatibility complex (MHC) proteins, coded by genes of the MHC, and unique to each individual.

    • T lymphocytes can only bind antigens that are presented on MHC proteins.

    • MHC proteins are involved in the recognition of "self" by the immune system and are crucial for transplantation compatibility.

    Cells of the Adaptive Immune Response

    • The adaptive immune system involves lymphocytes (B and T cells) and antigen-presenting cells (APCs).
    • B lymphocytes provide humoral immunity by secreting antibodies.
    • T lymphocytes provide cellular immunity by directly attacking infected cells, cancer cells, and foreign cells.
    • Antigen-presenting cells (APCs) engulf antigens and display fragments to T lymphocytes for recognition and activation.

    Lymphocyte Development, Maturation, and Activation

    • Lymphocytes develop from stem cells in the bone marrow.
    • B cells mature in the bone marrow while T cells mature in the thymus.
    • Lymphocytes undergo selection processes to ensure that they are immunocompetent (able to recognize and respond to antigens) and self-tolerant (do not attack self-antigens).
    • During activation, lymphocytes differentiate into effector cells or memory cells.

    Antigen Receptor Diversity

    • Lymphocytes have diverse antigen receptors that allow them to recognize a wide range of antigens.
    • This diversity is achieved through somatic recombination, a process that shuffles and combines gene segments during lymphocyte development.

    T Cell Education

    • T cell education ensures that T cells are able to recognize self-MHC proteins (positive selection) and do not attack self-antigens (negative selection).
    • T cells that fail either selection process undergo apoptosis (programmed cell death).

    Antigen-Presenting Cells (APCs)

    • APCs play an essential role in presenting antigens to T lymphocytes for activation.
    • Dendritic cells, macrophages, and B lymphocytes are the major types of APCs.
    • Dendritic cells, most effective antigen presenters, capture antigens and migrate to secondary lymphoid organs.
    • Macrophages present antigens to naive T cells and also perform phagocytosis and trigger inflammatory responses.
    • B lymphocytes present antigens to helper T cells for B cell activation.

    Overview of B and T Lymphocytes

    • B lymphocytes provide humoral immunity, secreting antibodies that target extracellular pathogens.

    • T lymphocytes provide cellular immunity, directly attacking infected cells, cancer cells, and foreign cells.

    • Helper T cells are crucial for coordinating both B and T cell responses.

      Activation and Differentiation of B Cells

    • Naive B cells are activated when their surface receptors bind to antigens.

    • Activated B cells undergo clonal selection, proliferating and differentiating into plasma cells (effector cells) and memory cells.

    • Plasma cells secrete antibodies specific for the antigen.

    • Memory cells provide immunological memory, mounting a faster and stronger response to future exposures to the same antigen.

    Immunological Memory

    • The primary immune response is the initial encounter with an antigen, leading to the generation of plasma cells and memory cells.
    • The secondary immune response is the subsequent encounter with the same antigen, characterized by a faster and more effective response due to memory cells.

    Active and Passive Humoral Immunity

    • Active humoral immunity is acquired through exposure to antigens, leading to the production of antibodies.
    • Passive humoral immunity is acquired through receiving antibodies from another source, providing temporary protection.

    Antibodies

    • Antibodies (immunoglobulins) are Y-shaped proteins secreted by plasma cells that bind specifically to antigens recognized by B lymphocytes.
    • Antibodies are grouped into five classes (IgG, IgA, IgM, IgE, and IgD), each with distinct characteristics, biological roles, and locations in the body.
    • IgG is the main antibody in secondary immune responses.
    • IgA is found in secretions to prevent pathogen entry.
    • IgM is the first antibody produced during a primary response.
    • IgE triggers histamine release from mast cells and basophils.
    • IgD functions as a B cell surface receptor.

    Immunoglobulin Classes

    • IgM is the first immunoglobulin class secreted during the primary immune response.
    • IgM readily activates complement.
    • IgM exists in monomer and pentamer (five united monomers) forms.
    • The monomer serves as an antigen receptor on the B cell surface.
    • The pentamer circulates in blood.
    • IgA is found in body secretions such as saliva, sweat, intestinal juice, and milk.
    • IgA helps stop pathogens from attaching to epithelial cell surfaces
    • IgA exists in monomer and dimer (two united monomers) forms.
    • The monomer exists in limited amounts in plasma.
    • IgD is found on the B cell surface.
    • IgD functions as a B cell antigen receptor (as does IgM).
    • IgG is the most abundant antibody in plasma, accounting for 75–85% of circulating antibodies.
    • IgG is the main antibody of both secondary and late primary responses.
    • IgG readily activates complement.
    • IgG protects against bacteria, viruses, and toxins circulating in blood and lymph.
    • IgG crosses the placenta and confers passive immunity from the mother to the fetus.
    • IgE is the major antibody of allergy and parasitic infections.
    • IgE stems bind to mast cells or basophils.
    • Antigen binding to the receptor ends triggers the release of histamine and other chemicals that mediate inflammation and an allergic reaction.
    • IgE is secreted by plasma cells in skin, mucosae of the gastrointestinal and respiratory tracts, and tonsils.

    Antibody Targets and Functions

    • Antibodies cannot destroy antigens; they inactivate and tag them for destruction and form antigen-antibody (immune) complexes.
    • Defensive mechanisms used by antibodies include:
      • Neutralization
      • Agglutination
      • Precipitation
      • Complement activation

    Clinical - Homeostatic Imbalance

    • Antibodies may be insufficient for infections by large parasitic worms.
    • IgE antibodies play a critical role in worm destruction by binding to their surface, marking them for destruction by eosinophils.

    Cellular Immunity

    • T cells provoke a cellular immune response when presented with antigens.
    • Some T cells directly kill cells infected by viruses or bacteria, cancerous or abnormal cells, or foreign cells.
    • Others release chemicals that regulate the immune response.
    • The two major T cell populations (CD4, CD8) are based on their cell differentiation glycoproteins.
    • Most CD4 cells become helper T (TH) cells that help activate B cells, other T cells, and macrophages and direct adaptive immune responses.
    • Some CD4 cells become regulatory T (TReg) cells that moderate the immune response.
    • Most CD8 cells become cytotoxic T cells (TC) capable of destroying infected, abnormal, or foreign cells.

    MHC Proteins and Antigen Presentation

    • T cells respond only to processed fragments of antigens displayed on the surfaces of cells by major histocompatibility complex (MHC) proteins
    • MHC proteins are classified as class I or class II.
    • Antigen presentation is required to activate naive T cells and for the normal functioning of effector T cells.
    • Class I MHC proteins are on the surface of virtually all body cells except RBCs.
    • Class I MHC proteins display endogenous antigens made inside the cell.
    • Healthy cells display fragments of normal body proteins (self-antigen).
    • Infected cells display parts of proteins that “belong” to the pathogen (antigen).
    • Cancer cells display pieces of abnormal proteins (antigen).
    • Class II MHC proteins are only on the surfaces of cells that present antigens to CD4 cells: dendritic cells, macrophages, and B cells.
    • Class II MHC proteins display exogenous antigens (antigens from outside the cell that have been engulfed by the cell displaying them).
    • MHC restriction:
      • CD4 cells are restricted to binding antigens only on class II proteins.
      • CD8 cells are restricted to binding antigens only on class I proteins.

    Activation and Differentiation of T Cells

    • T cells can only be activated by APCs.
    • T cell activation is a two-step process involving antigen binding and co-stimulation; both occur on the same APC and both are required for clonal selection.
    • Antigen binding triggers multiple intracellular signaling pathways that lead to T cell activation.
    • Co-stimulation is also required.
    • If a T cell does not bind to a co-stimulatory signal, it becomes unresponsive to antigens (called anergy), which is a safeguard against unwanted T cell activation.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    HAP12e Ch 21(1) PDF - Human Anatomy & Physiology

    Description

    Explore the essential components of the immune system in this quiz. Understand the three lines of defense against pathogens, including surface barriers, innate internal defenses, and adaptive responses. Test your knowledge on how the body protects itself from infections caused by microorganisms.

    More Like This

    Pathogens and Human Diseases
    30 questions

    Pathogens and Human Diseases

    MagicBixbite avatar
    MagicBixbite
    Immune System: Mucous Membrane and Pathogen Defense
    10 questions

    Immune System: Mucous Membrane and Pathogen Defense

    UnboundPhiladelphia avatar
    UnboundPhiladelphia
    Human Defence System Matching Quiz
    23 questions

    Human Defence System Matching Quiz

    ThrilledGyrolite avatar
    ThrilledGyrolite
    Defense Mechanisms in Immunology
    10 questions

    Defense Mechanisms in Immunology

    SpontaneousNourishment avatar
    SpontaneousNourishment
    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser