Immunology: Antibodies and Antigens

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Questions and Answers

What is the initial type of antibody that increases after immunization?

IgM (correct)

IgE

IgG

IgA

Which method is NOT used to produce monoclonal antibodies?

Synthetic antibody generation

Recombinant technology

Hybridoma technology

Passive immunization (correct)

Which of the following defines a hapten?

A component that enhances the immune response

A complete immunogen that can elicit an antibody response

A large protein that serves as an antigen

A small molecule that alone cannot elicit an immune response (correct)

Which of the following correctly describes hybridoma technology?

A fusion of immortal myeloma cells with antibody-producing B cells Signup and view all the answers

What increases in level after repeated immunization?

IgG Signup and view all the answers

Which of the following is NOT a function of antibodies?

Transporting oxygen in blood Signup and view all the answers

What is the primary function of antibodies?

To specifically bind to particular antigens Signup and view all the answers

Which of the following characteristics is NOT required for immunogenicity?

Small molecular size Signup and view all the answers

What defines an epitope in relation to antibodies?

A specific part of an antigen that binds to an antibody Signup and view all the answers

Which statement accurately describes the relationship between antigens and immunogens?

Some antigens must be attached to immunogens to elicit a response Signup and view all the answers

What happens to an antibody molecule when proteolytic enzymes cleave it?

It produces two identical Fab fragments and one Fc fragment Signup and view all the answers

Which part of the antibody is termed the paratope?

The specific region that binds to an antigen Signup and view all the answers

What is a hapten and how does it relate to immune responses?

An organic molecule that cannot trigger immune responses alone but can when attached to a carrier Signup and view all the answers

What distinguishes antibodies from other proteins?

Antibodies have a unique variable region for antigen binding Signup and view all the answers

Which type of chains make up an antibody molecule?

Heavy chains and light chains Signup and view all the answers

What is the primary function of IgM antibodies during an immune response?

To agglutinate bacteria and activate complement Signup and view all the answers

Which class of immunoglobulin is capable of crossing the placenta to provide protection to a newborn?

IgG Signup and view all the answers

What are the variations in the constant region of the heavy chain that result in different classes of antibodies called?

Isotype Signup and view all the answers

What is the term for the strength of the interaction between a paratope and its epitope?

Affinity Signup and view all the answers

What is the predominant form of IgA found in serum?

Monomer Signup and view all the answers

Which type of antibody variation is due to minor sequence differences between individuals?

Allotype Signup and view all the answers

What role does IgD play in the immune system?

Activation of B cells Signup and view all the answers

What type of interaction is NOT involved in the binding of antibodies to antigens?

Covalent bonds Signup and view all the answers

Which is true about IgE antibodies?

Linked to allergic reactions and parasitic infections Signup and view all the answers

What describes the number of different molecules that an antigen or an antibody can combine with at one time?

Valence Signup and view all the answers

What is the primary outcome of somatic hypermutation during an immune response?

Increased affinity for an antigen Signup and view all the answers

Which process directly retains antigen specificity while increasing functional diversity?

Class switching Signup and view all the answers

What role do cytokines and T cells play in class switching?

They influence the type of class switch that occurs. Signup and view all the answers

What is the function of activation-induced cytidine deaminase (AID) in antibody diversification?

Promotes class switching and somatic hypermutation Signup and view all the answers

How does the tissue environment affect isotype switching?

It influences the cytokines released by T cells. Signup and view all the answers

Which of the following is NOT a typical application of antibodies?

Direct activation of T cells Signup and view all the answers

What characterizes affinity maturation in the context of B cell responses?

Selects for increased affinity B cell receptors Signup and view all the answers

Which of the following is specifically altered during class switching?

The heavy chain constant region Signup and view all the answers

What is a significant effect of somatic hypermutation on B cell clones?

Generates clones with varying affinities Signup and view all the answers

Which of the following mechanisms directly contributes to the functionality of antibodies in diagnostics?

High specificity and selectivity of antibodies Signup and view all the answers

What phase of an infection is characterized by the first detection of antibodies against the infecting agent in the blood?

Seroconversion Signup and view all the answers

Which statement accurately describes the primary immune response?

It is short-lived and low in antibody levels. Signup and view all the answers

What process contributes to the initial diversity of the antibody repertoire?

V(D)J recombination Signup and view all the answers

Which of the following mechanisms significantly diversifies the antibody repertoire after initial formation?

Somatic hypermutation Signup and view all the answers

Which best describes the difference between the primary and secondary immune response?

The secondary response results in higher levels of antibodies compared to the primary response. Signup and view all the answers

What role do antigens have in the immune response according to the concept of clonal selection?

They activate specific clones of lymphocytes. Signup and view all the answers

What is the significance of somatic recombination during B cell development?

It allows for rearrangement of DNA segments to create diverse antibodies. Signup and view all the answers

Which statement about antibody diversity is NOT correct?

All antibodies are produced from a single genetic location. Signup and view all the answers

Which component is NOT involved in generating the antibody repertoire?

Gene splicing Signup and view all the answers

Study Notes

Antibodies

Antibodies are proteins that bind specifically to antigens.
Antibodies belong to the immunoglobulins (Igs) class of proteins.
Antibodies are secreted by differentiated B cells known as plasma cells.

Antigens and Immunogens

Antigens are molecules that can bind to antibodies or generate peptide fragments recognized by T cell receptors.
Immunogens are substances that elicit an adaptive immune response.
All antigens have the potential to elicit specific antibodies, but some need to be attached to an immunogen.
All immunogens are antigens, but not all antigens are immunogenic.

Immunogenicity Requirements

Foreignness
High molecular weight
Chemical complexity
Degradability

Haptens

Small organic molecules with simple structures that fail to induce immune responses.
An immune response can be provoked if a hapten is attached to a protein carrier.

Epitope, Paratope, and Antigen

Epitope: The specific portion of an antigen that binds to an antibody or T-cell receptor.
Paratope: The part of an antibody that recognizes and binds to the epitope (antigen binding site).

Antibody Molecule Fragments

Antibodies can be cleaved into functionally distinct fragments by proteolytic enzymes.
Two identical Fab (antigen binding) fragments
One Fc (crystallisable) fragment

Antibody Structure

Antibodies are composed of two types of protein chains:
- Heavy chains (2)
- Light chains (2)
The antigen binding region varies considerably between antibody molecules and is known as the variable or V region. The V region determines antigen specificity.
The constant region, or C region, is less variable and determines the effector functions of the antibody.

Immunoglobulin Classes

Five different immunoglobulin classes: IgM, IgD, IgG, IgA, and IgE.
Nine different isotypes.

Human Antibody Properties

IgM:
- The predominant antibody early in an immune response.
- It has 10 potential antigen-binding sites.
- Most effective antibody at agglutinating bacteria and activating complement.
IgD:
- Involved in B cell activation.
- Serum function is unknown.
IgG:
- The most prevalent antibody in serum.
- Able to cross the placenta to allow maternal protection of newborns.
IgE:
- Evolved to protect against parasitic infections.
- Involved in allergic reactions.
IgA:
- Present in serum and seromucous secretions.
- IgA1 is predominant in serum (over 80% is a monomer).
- IgA2 is the predominant antibody in seromucous secretions (saliva, colostrum, tracheobronchial, genitourinary secretions) and is a dimer.

Antibody Variations

Isotype: Variation in the constant region of the heavy chain that results in different antibody classes (IgG, IgM, IgA, IgD, IgE).
Allotype: Variation between individuals due to minor sequence differences in the heavy or light chains of antibodies.
Idiotype: Variation in the antigen binding region of different antibodies.

Antigen-Antibody Interactions

Affinity: The strength of the interaction between a single antigen binding site (paratope) and its epitope.
Valence: The number of different molecules that an antigen or antibody can combine with at one time.
Avidity: The strength of the interaction between multivalent antibodies and multivalent antigens.

Antigen-Antibody Bonds

Antibodies form multiple non-covalent bonds with antigens:
- Hydrogen bonds
- Electrostatic bonds
- Van der Waals forces
- Hydrophobic forces
- Cation-pi interactions

Specificity, Cross-Reactivity, and Non-Reactivity

Reactions can show a high level of specificity.
Reactions can also be cross-reactive, binding to structurally related but different antigens.

Immune Response and Antibody Secretion

Seroconversion: The phase of an infection when antibodies against the infecting agent are first detectable in the blood.
Primary Response: The first exposure to an antigen; slow, sluggish, short-lived, and low levels of antibodies.
Secondary Response: Second exposure to an antigen; faster, stronger, and longer-lasting response with higher antibody levels.

Clonal Selection Hypothesis

Antigens activate specific clones of lymphocytes.
This hypothesis explains how the immune system generates a highly diverse range of antibodies to target specific pathogens.

Antibody Repertoire Development

The immune system generates billions of different antibodies with a limited number of genes.
The diversity of the antibody repertoire is generated by:
- Somatic recombination
- Somatic hypermutation
- Class switching

V(D)J Recombination

Somatic recombination involves the rearrangement of gene segments within immunoglobulin during B cell development, in the absence of antigen.
The variable (V) region of an immunoglobulin heavy and light chain is encoded by more than one gene segment.

Somatic Hypermutation

Somatic hypermutation is the random mutation that occurs in the V region and diversifies the antibody repertoire.
This process alters the affinity of the antibody for antigens.
It occurs at the same time as class switching and both processes involve the enzyme activation induced cytidine deaminase (AID).

Affinity Maturation

Affinity maturation results from somatic hypermutation and increases antibody affinity for an antigen.
B cell receptors are selected for progressively higher affinity during an immune response

Class Switching

Class switching involves the C region of the heavy chain only and increases the functional diversity of antibodies.
Antigen specificity is retained.
Cytokines and T cells play a major role in class switching.
Isotype switching is greatly affected by the tissue environment, partly due to different cytokines released by T cells.

Antibody Applications

Diagnostics:
- Detection of infections
- Measurement of biological markers
- Recognition of allergies
Therapeutics:
- Treatment of cancer, infectious diseases, and autoimmune diseases.
Research:
- Immunohistochemistry
- Western blots
- Flow cytometry

Polyclonal Antibodies

Antibodies generated in a natural immune response or after immunization are polyclonal.

Monoclonal Antibodies

Monoclonal antibodies are produced by hybridoma technology or recombinant DNA technology.
Hybridoma technology: Fusion of an immortal myeloma cell with an antibody-producing B cell.
Recombinant technology: Synthetic antibodies or antibody fragments generated by recombinant DNA technology.

Antibody Levels After Immunization

After immunization, IgM levels increase first.
With repeated immunization, IgG levels increase.

Learning Objectives

Describe the basic structure of antibodies.
Understand the functions and properties of antibodies.
Define key terms related to immunology: antibody, antigen, epitope, paratope, immunogen, hapten, affinity, avidity, valency, idiotype, isotype, allotype.
Discuss antigen-antibody interactions.
Discuss the generation of the antibody repertoire.
Discuss the use of antibodies in therapeutics and diagnostics.
Discuss the preparation of monoclonal antibodies.

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Description

This quiz covers key concepts in immunology, focusing on antibodies, antigens, and their interactions. Explore the definitions, characteristics, and requirements for immunogenicity. Understand the roles of haptens and the distinctions between epitope and paratope.