Immunology: Clonal Selection and Antibody Structure

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Questions and Answers

What could be the consequence of a pathogen acquiring a mutation that altered the polypeptide sequence of its adhesion protein?

Increased adherence to host cells

Decreased ability to colonize host tissues (correct)

Enhanced immune system recognition

Complete loss of adhesion capabilities

Which of the following immune functions specifically targets pathogens that grow outside of host cells?

Cytotoxic T cell activation

Natural killer cell response

Antibody production (correct)

Phagocytosis by macrophages (correct)

Which mechanism would make a pathogen more effective in evading immune functions aimed at it?

Producing capsules that inhibit phagocytosis (correct)

Increasing permeability of bacterial membranes

Improving antigen presentation to T cells

Enhancing cytokine signaling

What is a primary difference between antigenic variation and antibiotic resistance in pathogens?

Antigenic variation alters pathogen structure for immune evasion, while antibiotic resistance alters susceptibility to drugs. Signup and view all the answers

Which type of pathogen would likely be more susceptible to a cytotoxic T cell response?

Intracellular viruses Signup and view all the answers

What is the role of clonal selection in the adaptive immune response?

It allows for the production of diverse antibodies. Signup and view all the answers

Which part of the immunoglobulin molecule is specifically responsible for binding to antigens?

Fab region Signup and view all the answers

What triggers a B cell to start secreting antibodies?

Activation by an antigen and T cell help Signup and view all the answers

Which antibody class is primarily involved in the anamnestic response?

IgG Signup and view all the answers

What distinguishes the primary B cell response from the memory B cell response?

Memory responses involve a faster and stronger reaction. Signup and view all the answers

How is the specificity of an antibody determined?

By the variable region of the heavy and light chains Signup and view all the answers

Which of the following statements best describes how ELISA assays detect antibodies?

They visualize antigen-antibody complexes through color change. Signup and view all the answers

What is the primary function of major histocompatibility complex (MHC) molecules?

To present antigens to T cells. Signup and view all the answers

What is the main role of antigen presentation by Major Histocompatibility Complex (MHC) class II proteins?

Presentation of extracellular antigens to helper T cells Signup and view all the answers

How is the diversity of antibody binding specificity primarily generated?

Through somatic recombination of immunoglobulin genes Signup and view all the answers

Which of the following best describes the relationship between pathogen growth and antigen presentation pathways?

Intracellular pathogens primarily activate MHC class I pathways, while extracellular pathogens activate class II Signup and view all the answers

What is a common feature of rapid chromatographic diagnostic tests?

They identify antigen-antibody complexes using colorimetric detection Signup and view all the answers

Which statement accurately reflects the function of T cells in the immune response?

T cells directly kill infected cells and help orchestrate the immune response Signup and view all the answers

Study Notes

Clonal Selection and Adaptive vs. Innate Immunity

Clonal selection is a fundamental process of adaptive immunity. It involves the activation of specific lymphocytes (B and T cells) whose receptors match a specific antigen. This leads to clonal expansion of these activated cells, resulting in a large number of effector cells, and memory cells that can quickly respond to later encounters with the same antigen.
Innate immunity, on the other hand, provides a rapid, non-specific response to pathogens through various processes like phagocytosis, inflammation, and the complement system. It does not have memory of specific antigens, meaning responses are not improved with repeated exposures to particular pathogens.

Immunoglobulin (Antibody) Structure and Diversity

Antibodies (immunoglobulins) are Y-shaped proteins made of four polypeptide chains (two heavy and two light).
The variable regions of the heavy and light chains form the antigen-binding sites.
Different binding specificities arise through variations in the amino acid sequences of these variable regions. This genetic diversity allows for enormous antibody diversity to recognize many different pathogens.
Antibodies bind to pathogen structures like surface proteins, polysaccharides, and toxins, but also the virus capsid, cell walls, and components of bacteria (e.g. flagella).

B Cell Development and Antibody Production

B cells develop from hematopoietic stem cells in bone marrow, undergoing maturation and selection processes.
Key events in development include rearrangement of immunoglobulin genes, expression of surface IgM, and negative selection to prevent self-reactive B cells.
B cells differentiate into plasma cells, which secrete antibodies, after receiving signals from T helper cells (specifically activated T helper cells), and B cells that become memory B cells—a crucial component in the memory response.
Memory B cells differentiate from activated B cells and are responsible for faster, higher antibody production during secondary exposure to the pathogen compared to a primary infection.

Antibody Classes and Isotype Switching

Different antibody classes (isotypes) like IgG, IgA, IgM, IgE, and IgD, have distinct functions (e.g., IgG in blood, IgA in mucosal surfaces, IgM in early immune responses).
Isotype switching involves a change in the constant region of the antibody, influencing its function without changing the antigen-binding specificity.
Antibody isotype switching does not involve the generation of new antigen specificities.

Memory B Cell Response

Memory B cells exhibit faster activation and higher antibody production upon second/later exposure to a pathogen compared to primary responses.
This rapid response is due to the increased numbers of memory B cells and their immediate differentiation into plasma cells, leading to a stronger immune response.

ELISA Assays

ELISA (enzyme-linked immunosorbent assay) is used to detect specific antibodies or antigens.
In tests to detect exposure, a capture antibody is placed on the surface and a labelled antibody is used in conjunction with a substrate. In tests to detect the presence of a pathogen, a known antigen is used on the surface and the labelled antibody is specific for that particular pathogen antigen.
Rapid diagnostic tests (e.g. urine test) differ from ELISA in speed and complexity.

Antigen Recognition by Antibodies and T Cells

Antibodies recognize and bind to the entire antigen, whereas T cells recognize specific peptide fragments presented by MHC molecules on the surface of other cells (antigen presentation).
T cells are key in coordinating immune responses. Their function varies depending on the type of T cell—helper T cells, and cytotoxic T cells.

MHC I and MHC II

MHC I presents intracellular peptides to cytotoxic T cells, triggering their destruction.
MHC II presents extracellular peptides to helper T cells, activating a wide range of immune responses.

Immune Response to Extracellular and Intracellular Pathogens

Immune response to extracellular pathogens involves phagocytosis, complement activation, and antibody production targeting the pathogen directly.
The immune response to intracellular pathogens, targeting virus infections inside cells or intracellular bacteria involves a complex interplay of cytotoxic T cells to destroy affected cells, with a more important role from helper T cells to amplify the intracellular response.

ABO Blood Group Antigens

ABO blood group antigens are carbohydrate molecules on red blood cells.
Individuals develop antibodies against ABO antigens not present on their own cells through exposure to these antigens in the environment.
Individuals with type O blood lack the A and B antigens and therefore do not produce antibodies against them, making them universal donors.

Inflammation, Septic Shock, and Anaphylaxis

Inflammation is a localized response to infection or injury, whereas septic shock is a systemic inflammatory response, and anaphylaxis is a life-threatening systemic allergic reaction.

Allergic Symptoms and Anaphylaxis

Allergic reactions involve the IgE-mediated activation of mast cells and basophils, leading to the release of inflammatory mediators and symptoms.
Anaphylaxis is a severe, potentially life-threatening allergic response involving the rapid release of mediators.

Penicillin and Pentadecylcatechols

Penicillin and pentadecylcatechols can induce an immune response due to their specific chemical structures or components that react with immune components.

Pathogen Adherence

Pathogens adhere to host cells through specific structures like pili and adhesins.
Mutations in adhesion proteins affect host cell binding, impacting pathogen colonization but they don't eliminate the production of adhesive structures.

Bacterial Toxins

Bacterial toxins, varying in their structure, have various mechanisms of secretion and targets within the host, some affecting cell signaling pathways, causing cell toxicity, or disruption of cellular functions.

Immune Evasion Mechanisms

Extracellular pathogens resist immune surveillance through various means, like hiding within tissues or producing toxins or inhibiting the complement system.
Intracellular pathogens employ mechanisms like preventing phagosome-lysosome fusion (to hide from innate immunity) and inhibiting cytotoxic T lymphocytes and other adaptive immune responses.

Anitgenic Variation and Antibiotic Resistance

Antigenic variation is a mechanism pathogens use to avoid immune recognition by changing their surface antigens.
Antibiotic resistance in pathogens is linked to genetic mutations or selective pressures in using antimicrobials.

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Description

Explore the concepts of clonal selection in adaptive immunity and the structure of antibodies. Understand how specific lymphocytes respond to antigens and how innate immunity differs by providing a rapid response. This quiz covers crucial immunological principles.