Immune System Overview

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Questions and Answers

What is one primary function of the immune system?

To elevate body temperature during infections

To protect the body against pathogens by differentiating self from non-self (correct)

To regulate hormonal balances in the body

To enhance nutrient absorption in the digestive tract

Which property of the immune system allows for a faster response to subsequent infections?

Diversity

Memory (correct)

Mobility

Specificity

Which of the following is a characteristic of innate immunity?

It includes a slower response time compared to adaptive immunity

It is specific to particular pathogens

It requires previous exposure to antigens for activation

It provides immediate defense against a wide range of pathogens (correct)

What role do MHC surface antigens play in the immune system?

They assist in recognizing and presenting foreign antigens to T-cells Signup and view all the answers

What is the significance of clonal expansion in the immune response?

It enables immune cells to replicate rapidly to combat pathogens Signup and view all the answers

Which class of immune cells is primarily responsible for antibody production?

B-cells Signup and view all the answers

How does the immune system's diversity benefit its function?

It enhances the ability to respond to a wide range of pathogens Signup and view all the answers

What is one factor contributing to T-cell diversity?

Genetic recombination during development Signup and view all the answers

What is the primary role of helper T-cells in the immune response?

Assist other immune cells with maturation and activation Signup and view all the answers

What is the primary function of cytotoxic T-cells?

Killing tumor cells and virally infected cells Signup and view all the answers

Which type of B-cell is responsible for rapid antibody production upon subsequent exposure to an antigen?

Memory B-cells Signup and view all the answers

In the context of the immune response, what do cytokines primarily serve as?

Signaling molecules mediating communication between cells Signup and view all the answers

What role do chemokines play in the immune system?

Mediating chemo-attraction between cells Signup and view all the answers

How do eicosanoids function in the immune response?

As mediators of inflammatory and immune responses Signup and view all the answers

What is the main role of regulatory T-cells in the immune system?

Suppress and regulate auto-reactive T cells Signup and view all the answers

Which molecules primarily mediate the acute inflammatory response?

Components of the innate immune system Signup and view all the answers

What is a key characteristic of B-cells during their maturation process in the bone marrow?

They only produce one type of antigen receptor Signup and view all the answers

Which of the following cytokines is primarily involved in antiviral responses?

Interferon Signup and view all the answers

What differentiates plasma cells from memory B-cells after B-cell activation?

Plasma cells primarily produce antibodies Signup and view all the answers

Which statement about the function of serotin is correct?

It plays a role in immune responses and homeostasis Signup and view all the answers

What physiological effect do prostaglandins primarily mediate in the body?

Vasodilation Signup and view all the answers

Which of the following cells are considered mediators of innate immunity?

Neutrophils Signup and view all the answers

What is the primary role of lymph nodes in the immune system?

Filter lymphatic fluid and house immune cells Signup and view all the answers

What distinguishes adaptive immunity from innate immunity?

It is antigen-specific and has memory Signup and view all the answers

Which part of a lymph node contains activated B cells developing into plasma cells?

Germinal center Signup and view all the answers

What is NOT a feature of innate immunity?

Recognizes specific antigens Signup and view all the answers

What is the function of dendritic cells within the immune system?

Act as antigen-presenting cells Signup and view all the answers

Which cells are primarily responsible for phagocytosis in peripheral tissues?

Macrophages Signup and view all the answers

What type of immunity is characterized by the activation of T-lymphocytes?

Adaptive immunity Signup and view all the answers

Which of the following statements about macrophages is FALSE?

They are the main contributors to adaptive immunity. Signup and view all the answers

What distinguishes CD4+ T-cells from CD8+ T-cells?

CD4+ T-cells are more numerous overall. Signup and view all the answers

How does the lymphatic system aid in immune surveillance?

By transporting lymph fluid containing immune cells Signup and view all the answers

What is the role of Toll-like Receptors (TLRs) in innate immunity?

To initiate the inflammatory response Signup and view all the answers

Where do T-lymphocytes mature after being produced in the bone marrow?

Thymus Signup and view all the answers

What is a primary difference between the cortex and medulla of a lymph node?

Medulla funnels immune cells for distribution; cortex does not. Signup and view all the answers

Which of the following is a characteristic of MHC Class I molecules?

Display epitopes from the cell's internal synthesis Signup and view all the answers

What is the primary function of cytotoxic T cells?

Recognize and destroy virally infected cells Signup and view all the answers

What does the positive selection process in the thymus ensure for T cells?

The T cells can recognize MHC I or MHC II antigens Signup and view all the answers

Which cells are primarily responsible for presenting antigens via MHC Class II?

Antigen-presenting immune cells Signup and view all the answers

What is the primary role of regulatory T cells?

Suppress immune responses against self antigens Signup and view all the answers

Which of the following correctly describes the process of T cell receptor (TCR) diversity?

Comes from recombination of V, D, and J segments Signup and view all the answers

What mechanism is primarily utilized by B cells for antigen recognition?

B cell receptors (BCRs) Signup and view all the answers

Which statement about memory B cells is true?

They proliferate upon re-exposure to an antigen Signup and view all the answers

How are T cells produced and matured?

Produced in the bone marrow, matured in the thymus Signup and view all the answers

What is the role of co-receptors CD4 and CD8 on T cells?

Assist in recognizing the specific MHC class Signup and view all the answers

What is a significant property of the Major Histocompatibility Complex (MHC)?

MHC molecules are polymorphic with over 2000 alleles Signup and view all the answers

What process ensures that T cells do not react against self-antigens?

Negative selection Signup and view all the answers

Which of the following is NOT a class of T cells?

Suppressor T cells Signup and view all the answers

What determines the specificity of a T cell receptor?

The genetic recombination of its chains Signup and view all the answers

What is the primary function of the variable region of an antibody?

To provide specificity and affinity to a singular antigen Signup and view all the answers

Which mechanism involves the clumping of antigen-containing pathogens for further destruction?

Agglutination Signup and view all the answers

What does class switching in antibodies result in?

Antibodies with the same Fab region but different Fc regions Signup and view all the answers

How does the complement system primarily enhance the immune response?

By coating pathogens to facilitate their recognition by phagocytes Signup and view all the answers

What is the role of Memory T-cells and B-cells in the acquired immune system?

To provide long-lasting protection against previously encountered pathogens Signup and view all the answers

Which immunoglobulin class is primarily involved in mucosal immunity?

IgA Signup and view all the answers

What is the membrane-attack complex (MAC) primarily responsible for?

Direct lysis of infected cells Signup and view all the answers

Which pathway of the complement activation is specific and dependent on antibody-antigen complexes?

Classical pathway Signup and view all the answers

What feature allows the immune system to recognize self versus non-self?

Specificity Signup and view all the answers

Which of the following describes opsonization?

Coating pathogens to aid in their phagocytosis Signup and view all the answers

Which property of the acquired immune system allows for a quicker response upon re-encountering an antigen?

Memory Signup and view all the answers

What is a characteristic of the innate immune system compared to the acquired immune system?

It does not have memory Signup and view all the answers

Which type of immune cell is involved in antibody-mediated cytotoxicity (ADCC)?

Macrophages Signup and view all the answers

What is the primary function of the aggregation of antibodies in the context of infection?

To block the entry of pathogens into host cells Signup and view all the answers

The protein components of the complement system are synthesized primarily in which organ?

Liver Signup and view all the answers

Study Notes

Immune System Properties

Protects against invaders by differentiating self from non-self.
Targets external pathogens (bacterial and fungal infections) and internal malignancies (cancer, viral transformations).
Repairs cellular damage.
Exhibits mobility for systemic protection.
Amplifies response through clonal expansion and signaling cascades.
Demonstrates specificity, preventing recognition of non-cross-reacting antigens.
Possesses memory for faster and stronger responses to subsequent infections.
Shows diversity in antigen receptors for recognizing numerous pathogens.

Immune System Organs and Lymphatic Circulation

Primary Lymphoid Organs: Bone marrow and thymus.
Secondary Lymphoid Organs: Lymph nodes, spleen, tonsils, adenoids, appendix, Peyer's patches, and mucosal-associated lymphoid tissues (MALT).
Lymph nodes are bean-shaped structures along lymphatic vessels, containing compartments for immune cell congregation and antigen encounter. They are divided into cortex (unactivated T cells), germinal center (activated B-cell development), para-cortex (mix of T cells), and medulla (funneling mature cells and antibodies). Humans typically have 500-600 lymph nodes.

Innate vs. Adaptive Immunity

Innate Immunity: First line of defense; rapid, short-term, non-antigen specific response. Utilizes pattern recognition receptors (PRRs), such as Toll-like receptors (TLRs), to recognize pathogen-associated molecular patterns (PAMPs) – highly conserved structures essential for microorganism survival or pathogenicity (e.g., LPS and mannose).
Cellular Mediators of Innate Immunity: Includes neutrophils, eosinophils, monocytes, natural killer (NK) cells, basophils (blood); macrophages, dendritic cells, mast cells (peripheral tissues); and tissue-specific monocytes (microglia, synovial A cells, etc.).
Adaptive Immunity: Specialized, adaptable, antigen-specific response; mediated by T and B lymphocytes, with help from antigen-presenting cells (APCs). It recognizes non-self in the presence of self, is clonal (each clone recognizes one antigen type), eliminates pathogens and infected cells, and generates immunological memory.
Cellular Mediators of Adaptive Immunity: T and B lymphocytes.

T-Cells

Produced in bone marrow, mature in thymus.
Target infected host cells (inaccessible to antibodies).
Types: Helper T cells (CD4+, activate B cells and cytotoxic T cells), Cytotoxic T cells (CD8+, kill infected cells), Memory T cells, Regulatory T cells (suppress auto-reactive T cells).

B-Cells

Form and mature in bone marrow.
Each B cell produces one type of antigen receptor (BCR), which is the precursor to antibodies.
Activated B cells differentiate into plasma cells (antibody production) and memory B cells (faster response upon re-exposure). Activated B cells can act as APCs.

Innate and Adaptive Immunity Interplay

Adaptive immunity is activated by and responds to innate immunity.

Time Course of Immune Response

Innate immunity provides a rapid initial response.
Adaptive immunity develops over time, providing a sustained and more specific response. Dysfunction of the adaptive immune response, as seen in severe COVID-19, can lead to overactive innate immunity and exaggerated cytokine responses.

Immune System Mobility and Replication

Inflammation, mediated by the innate immune system, is the acute response to injury and immune activation – involving cytokine release.

Inflammatory Response Mediators

Preformed and newly synthesized mediators are involved.

Protein Mediators of Immune Response: Cytokines

Soluble proteins, peptides, or glycoproteins that play significant roles in the inflammatory response.
Types: Chemokines (chemotaxis), Interleukins (various leukocyte functions), Interferons (antiviral responses), Tumor necrosis factor (TNF) family (immune and inflammatory regulation), Growth factors (blood cell production and immune regulation).

Chemical and Hormonal Mediators of Immune Response

Signaling molecules from immune and injured cells.
Include amino acid derivatives (histamine, serotonin), lipid derivatives (eicosanoids - prostaglandins and leukotrienes), and hormones (bradykinin, substance P).

Eicosanoids

Synthesized from arachidonic acid.
Include prostaglandins (vasodilation/constriction, vascular permeability) and leukotrienes (vasoconstriction, vascular permeability, chemotaxis, bronchoconstriction). Specific inhibition of eicosanoid biosynthesis enzymes is a key mechanism for controlling inflammation.

Immune System Specificity and Diversity

Recognition of self from non-self is crucial and involves major histocompatibility complexes (MHCs).

MHCs

Cell surface molecules presenting peptide epitopes.
Polymorphic, co-dominant, and polygenic.
MHC I: Present on all nucleated cells, display epitopes recognized by cytotoxic T cells.
MHC II: Present on APCs, display epitopes recognized by helper T cells.

T-Cell Antigen Recognition and Diversity

T-cell receptors (TCRs) are generated through genetic recombination of V, D, and J gene segments, creating diversity.
Positive selection in the thymus ensures affinity for MHC I or II.
Negative selection eliminates self-reactive T cells.

B-Cell Antigen Recognition and Diversity

Each B cell has a unique B-cell receptor (BCR).
BCR diversity arises from VDJ recombination.

Antibody Structure and Function (Immunoglobulins - Ig)

Y-shaped, composed of two light and two heavy chains.
Constant region (Fc) interacts with leukocytes and complement.
Variable region (Fab) confers antigen-specificity.
Class switching alters the Fc region, modifying antibody function.

Direct Cytotoxic Mechanisms

Antibodies bind to antigens with high specificity and affinity.
Antibody-mediated cytotoxicity involves interaction with immune cells and complement activation.

Second Recombination & Class Switching

Mature B-cell activation triggers a second recombination in the constant (Fc) region of the B-cell receptor (BCR).
This process is called class switching.
Class switching generates antibodies with the same antigen-recognition region (Fab) but different Fc regions.
This increases functional diversity by expanding the effector processes antibody binding can initiate.

Immunoglobulin Classes

Classified based on the heavy chain present (IgA, IgD, IgE, IgG, IgM).

Functional Outcomes of Antibody Binding

Antibody binding recruits cytotoxic immune cells and complement proteins, initiating destruction signals.
Agglutination: Clumping of antigen-containing pathogens, leading to phagocytosis.
Neutralization: Blocks active sites, preventing toxin binding and pathogen adhesion to host cells.
Opsonization: Coats pathogens for enhanced recognition by phagocytes.
Antibody-mediated cytotoxicity (ADCC): Natural killer cells (NKC), macrophages, neutrophils, and eosinophils use antibodies to detect infected cells. Fc receptor binding on cytotoxic cells triggers degranulation and apoptosis.
Inflammation: Amplifies the immune response and attracts immune effectors.
Complement activation: Leads to opsonization and formation of the membrane attack complex.

Complement System

Composed of ~30 small proteins and glycoproteins (designated "C," e.g., C1).
Primarily synthesized in the liver; constitutes ~5% of blood globulin.
Activation occurs via a cascade of proteolytic activities.

Activation Pathways of the Complement System

Three activation pathways:
- Classical Pathway: Activated by antigen-antibody complexes (adaptive/specific).
- Alternative Pathway: Non-specific (antibody-independent, C3 autolysis).
- Lectin Pathway: Activated by binding of specific carbohydrates on pathogens, aided by C-reactive proteins.

Functional Outcomes of Complement System Activation

Opsonization: Coats infected cells for phagocyte recognition.
Chemotaxis: Directs immune cells to infection sites (inflammation).
Infected-cell lysis: Formation of the membrane attack complex (MAC).

Direct Cell Lysis from Complement Activation

Membrane-attack complex (MAC): Formed by the classical, alternative, and lectin pathways on bacterial membranes. Multiple complement factors interact to form transmembrane channels, causing cell death via non-specific molecule and water diffusion.

Acquired Immune System: Memory

Memory T-cells and B-cells are generated upon initial pathogen contact.
Subsequent encounters produce faster, stronger responses.
This forms the basis of vaccination.
Immunocompromised individuals have weaker or shorter-lived responses.

Properties of the Immune System

Mobility: Systemic protection via rapid cell migration to infection sites.
Replication: Immune response amplification through clonal expansion and signaling cascades.
Specificity: Prevents recognition of non-cross-reacting antigens and distinguishes self from non-self.
Memory: Faster and stronger response to subsequent (similar) infections.
Diversity: Combinatorial library of antigen receptors allows recognition of numerous pathogens.

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Description

Explore the key properties and organs of the immune system in this informative quiz. Test your knowledge on its functions, cellular responses, and the role of primary and secondary lymphoid organs. Understand how the immune system protects the body against various pathogens and maintains health.