The Immune Response - Part 2
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Questions and Answers

What is one of the primary functions of antibodies in the adaptive immune response?

  • Bind and neutralize bacterial toxins and viruses (correct)
  • Inhibit the activity of T-cells
  • Increase the production of red blood cells
  • Enhance the formation of new B-cells

How do antibodies promote the process of phagocytosis?

  • By increasing the size of the pathogen
  • By directly attacking the pathogen's cell wall
  • By forming a protective barrier around the host cell
  • By coating the pathogen through opsonization (correct)

Which types of antibodies activate the complement system?

  • IgD and IgM
  • IgA and IgE
  • IgG and IgM (correct)
  • IgE and IgA

What is the ultimate goal of the adaptive immune response as indicated in the content?

<p>To target pathogens and their products for elimination (B)</p> Signup and view all the answers

Are antibodies specific or non-specific for their targets?

<p>Specific for their targets (A)</p> Signup and view all the answers

What is the primary function of the Fab fragment in antibodies?

<p>To bind to specific antigens (D)</p> Signup and view all the answers

Which regions are known as hypervariable regions in an antibody?

<p>Complementary-determining regions (CDRs) (C)</p> Signup and view all the answers

What is the role of the Fc fragment in antibodies?

<p>Binding to Fc receptors on immune cells (C)</p> Signup and view all the answers

During somatic recombination, which segments are joined to create the variable region of a light chain?

<p>One V segment and one J segment (C)</p> Signup and view all the answers

Which statement is true regarding epitopes and antibodies?

<p>B cells can recognize multiple epitopes of an antigen during an infection. (C)</p> Signup and view all the answers

What is the mass of a typical heavy chain in an antibody?

<p>Approximately 50 kD or more (A)</p> Signup and view all the answers

What is the main purpose of junctional diversity in B cell antigen recognition?

<p>To introduce additional variability in antibody structure (A)</p> Signup and view all the answers

What occurs when a B cell recognizes its specific antigen?

<p>It multiplies and produces clones. (C)</p> Signup and view all the answers

Which part of an antibody is involved in forming disulfide bonds?

<p>Fc fragment (A)</p> Signup and view all the answers

Why do B cells predominantly recognize external epitopes?

<p>B cells are primarily involved in detecting surface infections. (D)</p> Signup and view all the answers

What is the main purpose of junctional diversity in B cell development?

<p>To add new and random nucleotides to gene segments (C)</p> Signup and view all the answers

During B cell development, what is generated first?

<p>Heavy chain (A)</p> Signup and view all the answers

What class of antibody is first secreted during an infection?

<p>IgM (C)</p> Signup and view all the answers

What is the role of helper T cells in B cell activation?

<p>To regulate the activities of other immune cells (A)</p> Signup and view all the answers

What role do MHC molecules play in the immune response?

<p>They help to regulate tissue transplantation. (A), They assist in the activation of T-cells. (D)</p> Signup and view all the answers

What initiates class switching in B cells?

<p>T cell help (C)</p> Signup and view all the answers

What are the different isotypes of MHC molecules expressed in humans?

<p>Six MHC class I isotypes and five MHC class II isotypes. (C)</p> Signup and view all the answers

What is the term used for the specific version of a protein encoded by an allele?

<p>Allotype (D)</p> Signup and view all the answers

Which of the following best describes Class I MHC molecules?

<p>They present infected cell peptides to CD8+ T cells (A)</p> Signup and view all the answers

What is the first step of B cell antigen recognition diversity?

<p>Combinatorial diversity (C)</p> Signup and view all the answers

How do MHC class I and class II proteins differ at a structural level?

<p>Class I proteins consist of only alpha chains while class II includes beta chains. (A)</p> Signup and view all the answers

What happens to B cells that do not encounter an antigen?

<p>They undergo apoptosis (B)</p> Signup and view all the answers

What inheritance pattern do MHC alleles typically follow?

<p>Individuals inherit one allele from each parent, which may be the same or different. (D)</p> Signup and view all the answers

What does the polymorphism in MHC genes refer to?

<p>The presence of multiple different alleles for each isotype within a population. (A)</p> Signup and view all the answers

MHC Class II molecules are recognized by which type of T-cell receptors?

<p>CD4+ helper T-cell receptors (B)</p> Signup and view all the answers

Which statement accurately reflects the expression of MHC proteins?

<p>All nucleated cells in higher vertebrates express MHC proteins. (B)</p> Signup and view all the answers

What occurs to B cells after they leave the bone marrow?

<p>They circulate through blood and lymph (B)</p> Signup and view all the answers

What is a consequence of the variability of MHC proteins in a population?

<p>Greater difficulty in matching organ donors with recipients. (D)</p> Signup and view all the answers

What process ensures B cells do not have strong recognition of self before leaving the bone marrow?

<p>Selection process (B)</p> Signup and view all the answers

What feature is common to heavy chain types in antibodies?

<p>They determine antibody class (C)</p> Signup and view all the answers

What is the significance of combinatorial diversity in B cells?

<p>It enables the creation of diverse antibodies (B)</p> Signup and view all the answers

What molecules do cytotoxic T cells primarily recognize?

<p>MHC Class I molecules (A)</p> Signup and view all the answers

What is the first class of antibody secreted by a B-cell during an immune response?

<p>IgM (B)</p> Signup and view all the answers

Which type of MHC molecule is recognized by CD8+ cytotoxic T-cells?

<p>MHC Class I (B)</p> Signup and view all the answers

What role do TFH cells play in the B-cell response?

<p>They help B-cells differentiate into plasma or memory cells. (C)</p> Signup and view all the answers

Which cells have MHC Class II molecules on their surface?

<p>Dendritic cells, B-cells, and macrophages (B)</p> Signup and view all the answers

Where do long-lived plasma cells migrate to in order to provide a systemic source of antibodies?

<p>Bone marrow (C)</p> Signup and view all the answers

What is required for B-cells to secrete antibodies?

<p>Helper T-cell assistance (B)</p> Signup and view all the answers

Which statement best describes class switching of B-cells?

<p>It changes the class of antibody the B-cell produces. (B)</p> Signup and view all the answers

What is the primary function of memory T-cells?

<p>To remember past infections and respond quickly upon re-exposure (B)</p> Signup and view all the answers

What is the unique feature of inducible T cell costimulator (ICOS)?

<p>It enhances B-cell responses. (A)</p> Signup and view all the answers

How does a T-cell receptor recognize an antigen?

<p>When the antigen is presented by an MHC molecule (C)</p> Signup and view all the answers

What is the primary effect of MHC molecule heterogeneity on T-cell activation?

<p>It allows a wider variety of peptides to be presented. (C)</p> Signup and view all the answers

What is the primary role of dendritic cells in T-cell activation?

<p>To present antigens to T-cells. (A)</p> Signup and view all the answers

What happens to T-cells if they do not encounter their specific antigen?

<p>They undergo apoptosis. (A)</p> Signup and view all the answers

Which characteristic is true for T-cell precursors in the thymus?

<p>They do not express CD4 or CD8. (D)</p> Signup and view all the answers

How many MHC Class I allotypes can a typical individual express?

<p>Up to 12 (C)</p> Signup and view all the answers

What is the outcome of T-cell activation after encountering antigen presented by dendritic cells?

<p>They proliferate and differentiate. (C)</p> Signup and view all the answers

What type of T-cells can help B-cells produce antibody molecules?

<p>CD4+ T-cells (D)</p> Signup and view all the answers

What occurs when T-cells bind to antigens presented by dendritic cells?

<p>They undergo signal transduction pathways leading to activation. (D)</p> Signup and view all the answers

What does seroconversion signify in the context of HIV infection?

<p>The production of detectable antibodies. (C)</p> Signup and view all the answers

What role does the MHC play in the immune response?

<p>It provides a mechanism for antigen presentation. (C)</p> Signup and view all the answers

How do cytotoxic T-cells engage with their targets?

<p>By directly killing virus-infected cells. (C)</p> Signup and view all the answers

Why is MHC polymorphism important for population immunity?

<p>It increases the diversity of antigen presentation. (B)</p> Signup and view all the answers

What happens to T-cells after they are continuously activated in lymph nodes?

<p>They proliferate and can differentiate into effector cells. (C)</p> Signup and view all the answers

What initiates the signaling within a T-cell upon binding to a peptide:MHC complex?

<p>Lck phosphorylation of ITAMs. (B)</p> Signup and view all the answers

Flashcards

Humoral immunity

An adaptive immune response that uses antibodies to neutralize pathogens and their products.

Antibodies

Proteins that bind to and neutralize pathogens, promoting elimination by phagocytes.

Antibody function: neutralization

Antibodies bind to and inactivate harmful substances like toxins, viruses, and bacteria.

Antibody function: opsonization

Antibodies coat pathogens, making them easier for immune cells to engulf and destroy.

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Antibody function: complement activation

Antibodies trigger a cascade of proteins that enhance pathogen destruction and inflammation.

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Antibody structure

Antibodies are composed of two identical light chains and two identical heavy chains. Each light chain is linked to a heavy chain by a disulfide bond, and both pairs are linked by disulfide bonds. Each light chain has a variable region and a constant region of one domain. Each heavy chain has a variable region and a constant region of 3 or 4 domains.

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Fab fragment

The Fab fragment of an antibody is composed of the light chain and part of the heavy chain. It is responsible for recognizing and binding to antigens.

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Fc fragment

The Fc fragment of an antibody is a portion of the constant region of the heavy chain. It interacts with immune cells and activates their functions.

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Epitope

An epitope is the specific part of an antigen that an antibody binds to. It's like a tiny 'flag' on the pathogen that the antibody recognizes.

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B-cell response to antigen

When a B-cell recognizes its specific antigen, it multiplies and produces clones of itself, all secreting the identical antibody that binds to the same epitope on the antigen.

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Different epitopes

Different B-cells can recognize the same antigen but bind to different epitopes on it, creating a diverse response to the pathogen.

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External epitopes

B-cells tend to recognize epitopes that are located on the surface of the pathogen, making them easier to access and target by antibodies.

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Hypervariable regions (CDRs)

Hypervariable regions (CDRs) are short stretches of amino acids within the variable region of an antibody that are highly diverse. These regions are responsible for the specific recognition of antigens.

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Somatic Recombination

Somatic recombination is the process of joining different DNA segments (V, D, and J segments) in a random fashion to generate a diverse pool of antibody variable regions. This process occurs during B-cell development.

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Junctional Diversity

During somatic recombination, nucleotides can be added or removed at the junctions between V, D, and J segments, further increasing the diversity of antibody variable regions.

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MHC Molecules

Proteins found on the surface of cells that present antigens to T cells, triggering an immune response. They play a crucial role in tissue transplantation.

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HLA Antigens

MHC proteins found in humans, specifically human leukocyte antigens, which are key players in the immune system's recognition and response to foreign molecules.

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MHC Class I

A type of MHC molecule expressed on all nucleated cells, presenting internal antigens to CD8+ cytotoxic T cells, leading to the destruction of infected or cancerous cells.

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MHC Class II

A type of MHC molecule expressed primarily on antigen-presenting cells (APCs) like macrophages, presenting external antigens to CD4+ helper T cells, initiating an immune response.

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MHC Polymorphism

The high diversity of MHC genes within a population, with many different versions (alleles) of each gene, leading to a diverse range of MHC proteins.

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MHC Allele

A specific version of an MHC gene, leading to a particular protein variant. Individuals inherit one allele from each parent.

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MHC Allotype

The specific protein encoded by a particular MHC allele, contributing to the individual's unique MHC profile.

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MHC Complement

The entire set of MHC proteins expressed on an individual's cells, influenced by the inherited MHC alleles.

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V(D)J Recombination

A process where DNA segments called V, D, and J are rearranged to create unique antibody genes. This creates diversity in the antigen-binding region of antibodies.

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CDR3

The hypervariable region of the antibody, primarily determined by junctional diversity, and responsible for antigen binding.

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Combinatorial Diversity

The combination of different heavy and light chains to produce a vast repertoire of antibodies.

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B-cell Differentiation

The process of B-cell maturation, starting with immature B cells in the bone marrow and ending with mature, antigen-specific B cells in the circulation.

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Clonal Expansion

The rapid proliferation of antibody-producing B cells upon encountering an antigen.

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IgM

The first class of antibody produced by B cells, expressed on the surface of naive B cells.

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Class Switching

The process where B cells switch from producing IgM to other antibody classes like IgG, IgA, or IgE, after encountering antigen and with help from T cells.

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T-cell Help

The support and activation provided by helper T cells (specifically TFH cells) to B cells for antibody production and class switching.

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Professional Antigen Presenting Cell (APC)

Cells that are specialized for capturing and presenting antigens to T cells, such as macrophages, dendritic cells, and B cells.

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Antigen Processing

The breakdown of antigens into smaller peptide fragments that can be presented by MHC molecules.

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T-cell Receptor

A receptor on T cells that recognizes antigen presented by MHC molecules, crucial for initiating immune responses.

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Cytotoxic T cells (CD8+)

T cells that kill virus-infected cells or cancerous cells, recognizing MHC Class I.

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What is the role of T cells in B cell activation?

Helper T cells (TFH) assist B cells by providing signals that trigger antibody secretion.

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What class of antibody is secreted first?

IgM is the initial antibody class secreted by B cells during an immune response.

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What determines if a B cell becomes a plasma or memory cell?

Follicular helper T cells (TFH) influence B cell differentiation into either antibody-producing plasma cells or long-lived memory cells.

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What is class switching?

Class switching is where B cells change the type of antibody they produce. This helps target specific pathogens.

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What is MHC?

Major Histocompatibility Complex (MHC) are molecules on cell surfaces that display fragments of antigens.

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What's the difference between MHC Class I and II?

MHC Class I presents antigens to CD8+ cytotoxic T cells, found on all nucleated cells. MHC Class II presents antigens to CD4+ helper T cells, found on antigen-presenting cells.

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What are the functions of a CD8+ cytotoxic T cell?

CD8+ T cells recognize virus-infected cells and directly kill them through the release of cytotoxic molecules.

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What is the function of a plasma cell?

Plasma cells are the antibody-producing factories of the immune system, generating large amounts of specific antibodies.

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What is the difference between primary and secondary antibody responses?

A primary response is the initial encounter with an antigen, leading to slower antibody production. A secondary response is faster, stronger, and more effective due to memory cells.

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What are the effector functions of antibodies?

Antibodies neutralize pathogens, promote phagocytosis (opsonization), and activate complement to enhance immune responses.

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MHC Expression

Each cell expresses MHC molecules from both the maternal and paternal chromosomes. This results in the expression of multiple MHC allotypes (different versions of the same MHC gene) on the cell surface.

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MHC and Peptide Presentation

Each MHC molecule presents a range of peptides (not just one). This variety ensures the immune system can recognize a wider spectrum of antigens.

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MHC Heterozygosity

The presence of different MHC allotypes from both parents, resulting in a wider range of peptides presented by the immune system.

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MHC and Disease Resistance

Individuals with greater MHC heterozygosity are often associated with better resistance to certain diseases. This is because they can present a wider range of peptides, increasing the chance of recognizing and responding to diverse pathogens.

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T-cell Function

T-cells recognize antigens in the context of MHC molecules. CD4+ T-cells recognize antigens on Class II MHC molecules, while CD8+ T-cells recognize them on Class I MHC molecules.

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T-cell Development

T-cells originate in the bone marrow and mature in the thymus. During maturation, they become either CD4+ or CD8+.

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T-cell Activation

T-cells are activated in lymph nodes by dendritic cells presenting pathogen-derived antigens in the context of MHC molecules. This leads to T-cell proliferation and differentiation into effector T-cells.

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Effector T-cell Function

Effector T-cells perform specific functions depending on their specialization. CD4+ helper T-cells assist B-cells in antibody production, while CD8+ cytotoxic T-cells kill virus-infected cells.

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T-cell Receptor Scanning

Naïve T-cells actively scan dendritic cells for their specific antigen presented in the context of MHC molecules. If they encounter their antigen, they become activated.

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T-cell Activation Signals

Binding of the T-cell receptor to the antigen-MHC complex triggers a signaling cascade within the T-cell, leading to its activation and proliferation.

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T-cell Signaling Pathway

The signaling pathway involves phosphorylation of ITAMs, activation of Lck and ZAP-70 kinases, and downstream signaling events leading to T-cell activation.

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T-cell Proliferation

Once activated, T-cells undergo rapid proliferation, creating an army of effector T-cells capable of responding to the specific antigen.

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T-cell Effector Function

After activation and proliferation, effector T-cells leave the lymph node and migrate to sites of infection to carry out their specific functions.

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Study Notes

The Immune Response - Part 2

  • The adaptive immune response involves B-cells, T-cells, and dendritic cells.
  • Healthy skin is not inflamed.

B-cells, T-cells and Dendritic cells

  • Surface wounds introduce bacteria, activating resident effector cells to secrete cytokines.
  • Vasodilation and increased vascular permeability allow fluid, proteins, and inflammatory cells to leave the blood and enter tissue.
  • The infected tissue becomes inflamed, causing redness, heat, swelling, and pain.
  • Macrophages engulf bacteria in infected tissue.
  • Afferent lymphatic vessels carry lymph from infected tissue.

Phases of the Immune Response

  • Innate immune response: Inflammation, complement activation, phagocytosis, and pathogen destruction occur within minutes to days.
  • Adaptive immune response:
    • Antigen-presenting dendritic cells interact with antigen-specific T cells, promoting T-cell proliferation and differentiation (hours to days).
    • Antigen-specific B cells are activated (hours to days).
    • Effector and memory T cells are formed (days to weeks).
    • T cells interact with B cells, forming germinal centers and producing effector B cells (plasma cells) and memory B cells that produce antibody (days to weeks).
    • Effector lymphocytes emigrate from peripheral lymphoid organs (a few days to weeks).
  • Immunological memory: Maintenance of memory B and T cells with high antibody levels for protection against reinfection (days to weeks or lifelong).

Antibodies

  • Antibodies are the secreted form of the BCR and are specific.
  • Antibodies bind to and neutralize bacterial toxins, viruses, and bacteria.
  • They coat pathogens (opsonization), promoting phagocytosis.
  • They activate complement (IgG and IgM).
  • Antibodies are highly folded, specific, and bind to epitopes to target pathogens.
  • Antibodies consist of two identical light chains (~25 kD) and two identical heavy chains (~50 kD or more).
  • Each light chain is joined to a heavy chain by a disulfide bond.
  • Each light chain/heavy chain dimer is connected by disulfide bonds.
  • Each light chain has a variable region and a constant region (of one domain).
  • Each heavy chain has a variable region and a constant region (of 3 or 4 domains).
  • Fab fragment (fragment antigen binding) is composed of light and part of a heavy chain.
  • Fc fragment (fragment crystalizable) is a portion of the heavy chain's constant region.
  • The Fc region of antibodies binds to Fc receptors on cells like macrophages.
  • Antibodies are the secreted form of the B-cell receptor and are specific for one antigen-binding site (epitope).

Antibody Structure and Function

  • Antibodies consist of two identical light chains and two identical heavy chains, connected by disulfide bonds.
  • Each light chain has a variable region (VL) and a constant region (CL).
  • Each heavy chain has a variable region (VH) and constant region(s) (CH).
  • The six hypervariable regions (CDRs) form the antigen-binding site.
  • Two light chains and two heavy chains combine to form the antibody structure.
  • Different classes of antibodies (IgM, IgG, IgA, IgE, IgD) have distinct roles.

Generation of B Cell Antigen Recognition Diversity

  • Step 1: Somatic Recombination: Generates the variable regions in light and heavy chains.
    • Light chain: Joins one V segment and one J segment.
    • Heavy chain: Joins one V, one D, and one J segment.
  • Step 2: Junctional Diversity: Adds new and random nucleotides at V and J segments.
  • Step 3: Combinatorial Diversity: Combines the variable regions.
  • B-cells in bone marrow produce heavy chain first, followed by light chain, then undergo specific selection.

What happens when B and T cells leave the bone marrow

  • B cells circulate between blood and lymph.
  • B cells phagocytose antigen in lymph node.
  • B cells require T cell help to secrete antibody.
  • B cells process antigen to present on their surface in context of MHC molecule.

T Cell Structure and Function

  • Helper T cells (CD4+): Regulate other white blood cells.
  • Cytotoxic T cells (CD8+): Kill virus-infected cells.
  • Regulatory T cells: Suppress the immune response.
  • T helper cells help activate macrophages, B cells and cytotoxic T Cells.
  • T cell precursors develop in thymus from bone marrow.
  • CD4+ or CD8+ T-cells mature in thymus and emerge.
  • Naive T cells circulate between blood and lymph.
  • T cells recognize antigen complexes on antigen presenting cells.
  • T cells are activated in lymph nodes.
  • When activated, T cells proliferate and differentiate.

MHC Molecules

  • MHC molecules present antigens to T cells.
  • Class I MHC molecules are on all nucleated cells and present endogenous antigens.
  • Class II MHC molecules are on antigen-presenting cells and present exogenous antigens.

Antigen Processing and Presentation

  • Pathogen pieces are bound to MHC class I or II molecules.
  • MHC molecules present antigen fragments on cell surfaces.

T-cell Receptor Function

  • The T-cell receptor recognizes antigen only when presented by an MHC molecule.
  • CD4 binds to the B2 domain of MHC II.
  • CD8 binds to the α3 domain of MHC I.

Effector Functions of T Cells

  • Cytotoxic T cells kill virus-infected cells.
  • Helper T cells activate macrophages, B cells, and other components of the immune system.

B-cell Differentiation and Antibody Production

  • TFH cells determine if B cells become plasma or memory cells, and help activate B cells.

Antibody Response

  • The primary response to an antigen produces IgM first.
  • The secondary response is faster and stronger because of immunological memory.

Summary

  • Different cell types and actions work together during immune response.
  • Helper T cells play a critical role in activating B-cells and other immune responses.
  • Antibody responses vary based on mechanisms of recognition and binding to antigens, leading to diverse and adaptive responses.

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Chapter 17.2: The Immune Response (PDF)

Description

Dive deeper into the adaptive immune response, focusing on B-cells, T-cells, and dendritic cells. This quiz covers the phases of the immune response, mechanisms like phagocytosis, and the role of inflammation. Test your understanding of these crucial immune functions.

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