Immunology Week 1: Antigen Recognition

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Questions and Answers

Which immunoglobulin classes are present as antigen receptors on naïve B-lymphocytes?

IgM & IgD (correct)

IgA & IgD

IgE & IgD

IgG & IgD

What is the main function of the Ig α and Ig β proteins in the B-cell receptor?

Anchor the receptor in the membrane

Bind antigens directly

Facilitate class switching

Transmit activation signals (correct)

In T-cell receptors (TCR), which domain is most variable among the complementarity-determining regions?

CDR3 (correct)

CDR2

CDR1

CDR4

What is the role of CD4 and CD8 in T-cell activation?

Connect TCR to MHC molecules Signup and view all the answers

What describes the strength of binding of an antibody to an epitope?

Affinity Signup and view all the answers

What type of antigens can B cell receptors (BCR) recognize?

Proteins, carbohydrates, lipids, and nucleic acids in their native forms Signup and view all the answers

Which component of the immunoglobulin structure is specifically responsible for determining antibody isotype/class?

Type of heavy chain Signup and view all the answers

What role do hypervariable regions (CDRs) play in immunoglobulins?

Contribute to the specificity of antigen binding Signup and view all the answers

How does T cell receptor (TCR) recognition differ from B cell receptor (BCR) recognition?

BCR can recognize a wider variety of antigens compared to TCR Signup and view all the answers

What functional role does the 'Fc' region of an antibody serve?

Engaging with immune cells and mediating effector functions Signup and view all the answers

Which antibodies are characterized by the presence of a heavy chain type 'α'?

IgA Signup and view all the answers

What key distinction exists between affinity and avidity in the context of antibodies?

Affinity refers to the binding strength of a single antibody to an antigen, while avidity accounts for multiple binding interactions Signup and view all the answers

What defines the total number of distinct lymphocyte clones within the immune system?

Immune repertoire Signup and view all the answers

What is the primary function of the Ig α and Ig β proteins in the BCR complex?

They transmit activation signals after antigen binding. Signup and view all the answers

Which components constitute the TCR complex?

TCR, CD3, and ζ protein. Signup and view all the answers

What distinguishes the process of affinity maturation in antibodies?

It involves enhancing the strength of binding to an antigen after repeated stimulation. Signup and view all the answers

What determines the specific class or isotype of an antibody?

The type of heavy chain present in the antibody. Signup and view all the answers

How does heavy chain class switching affect the properties of the antibody?

It alters the physical and biological properties of the antibody. Signup and view all the answers

What is the primary structural difference between T cell receptors (TCR) and B cell receptors (BCR)?

TCR recognizes processed peptides on MHC, whereas BCR recognizes native antigens. Signup and view all the answers

Which component of the immunoglobulin structure is crucial for its diverse antigen recognition?

The hypervariable regions (CDRs). Signup and view all the answers

What is the role of the 'Fc' region in an antibody's structure?

To drive effector functions and interact with other immune components. Signup and view all the answers

Which of the following statements best describes the 'hinge region' of an immunoglobulin?

It allows flexibility for antigen binding. Signup and view all the answers

What determines the antibody isotype/class?

The heavy chain type in the antibody. Signup and view all the answers

What is the significance of heavy chain class switching in antibodies?

It enables the generation of antibodies with different effector functions. Signup and view all the answers

Affinity and avidity differ primarily in which way?

Affinity refers to overall binding strength, while avidity refers to single interactions. Signup and view all the answers

What characterizes monoclonal antibodies?

They are identical antibodies produced by a single clone of B cells. Signup and view all the answers

Study Notes

Overview

King Faisal University College of Medicine
Practical Infectious Diseases Week 1
Division of Microbiology

Vision

Become a model in community engagement, through excellence and international recognition in medical education, research, and healthcare.

Mission

Promote higher standards in medical education, healthcare, research, and community health services.

Values

Islamic values
Excellence
Creativity
Compassion
Leadership
Responsiveness to community

Antigen Recognition

CRN No: 15569(Male), 15581 (Female)
Block: 1.2
Subject/Discipline: Immunology
Expert: Dr.Sayed A.Quadri
Block Coordinator: Dr.Sayed A.Quadri

Learning Questions

What are the similarities and differences between antigen receptors on B and T lymphocytes?
Describe membrane immunoglobulin and T cell receptors, and explain why and how they're expressed as complexes on lymphocytes.
Explain 'class' and 'subclass' in antibodies, including heavy chain class switching and affinity maturation.
Explain the differences between affinity and avidity.
What are monoclonal antibodies?

Immune Repertoire

Each lymphocyte has unique antigen specificity.
The total number of distinct lymphocyte clones is called the immune repertoire.

Similarities and Differences Between B and T Cell Receptors

TCR and BCR recognize different structures.
BCRs can recognize proteins, carbohydrates, lipids and nucleic acids in their native forms.
TCRs recognize processed peptide antigens displayed on APCs with MHC.
Both antigen receptors (ARs) have variable regions for antigen binding and constant regions for structural integrity and effector functions.
Both ARs are attached to other molecules delivering activation signals after antigen recognition.

Forms of Antigens Recognized

Macromolecules (proteins, polysaccharides, lipids, nucleic acids), small chemicals
Conformational and linear epitopes

Diversity

Each clone has unique specificity; potential for > 109 (BCR) and > 10^11 (TCR) distinct specificities.
Variable regions of heavy and light chains of membrane Ig or a and β chains

Antigen Recognition and Antibody Binding

Antigen recognition mediated by variable regions of heavy and light chains.
Signaling functions mediated by Igα and Igβ proteins.
Effector functions mediated by constant regions of secreted Ig.
TCRs do not perform effector functions

Antibody Binding

Linear (continuous) and conformational (discontinuous) epitopes.

Antibody Structure (IgG & IgM)

Secreted IgG has 4 polypeptide chains (2 heavy, 2 light) forming a 'Y' structure.
Heavy chain has 3 constant domains (CH1, CH2, CH3).
L chain has 2 domains (VL, CL).
3 hypervariable regions (CDRs) on VL & VH with CDR3 showing the highest variability.
IgM is a pentamer and has 10 antigen binding sites.
Variable regions for Antigen binding
Constant regions for Structural integrity/effector functions.
Fab: antigen binding regions
Fc: constant regions
Hinge regions connect Fab to Fc

Antibody types

IgA, IgD, IgE, IgG, and IgM.
Differences in heavy chain type determine class/isotype of Antibody.

Secreted lg structure

L chain (VL & CL) + Part of H chain (VH & CH1) - 2 Fab regions/Ig.
CH2 &CH3 -'Fc' region- 1 Fc region/Ig.
Hinge region between Fab and Fc.
'C' terminal anchored to plasma membrane in membrane Ig.

Class/Isotype types

5 types of H chains - μ, δ, γ, ε & α
Antibody Isotype/Class – determined by heavy chain type.
IgM, IgD, IgG, IgE, & IgA: Each has unique physical and biological properties.
Presence of IgM/IgD in membrane-bound form on naïve B-lymphocytes.

Antigen Epitope

Epitope is the part of antigen recognized by an antibody.

B-Cell Receptor (BCR)

BCR = Membrane Ig + 2 proteins (Igα and Igβ)
BCR activation by antigen binding.

T-Cell Receptor (TCR)

TCR = α & β chain with each chain having a constant ('C') and variable ('V') domain.
Each 'V' domain has 3 CDRs (complementarity-determining regions).
CDR3 shows the highest variability.
Both chains anchored to the membrane. Other types of chains possible (γ and δ).

TCR Complex

TCR complex is TCR + CD3 + ζ protein
CD3 & ζ transmit signals

TCR Complex Co Receptors

CD4 or CD8 are co-receptors
CD4 & CD8 bind to non-polymorphic region of MHCII/MHCI

Antibody Class and Subclass

Heavy chain type determines the class/isotype.
5 classes: IgM, IgD, IgG, IgE, and IgA - each has distinct physical & biological properties

Heavy Chain Class Switching

Initially B-lymphocytes secrete IgM and later other classes (heavy chain switching or isotype switching).
Even after switching, antigenic specificities do not change.

Antibody Affinity and Avidity

Affinity is strength of antibody binding to an epitope.
Expressed as Dissociation constant (Kd).
Avidity is total strength of binding to an antigen..

Antibody Affinity Maturation

Antibodies in primary immune response (IR or Sec.IR) have low affinity, but with stimulation, affinity increases - Affinity Maturation

Monoclonal Antibodies

Produced by a single clone of B-cells
Have single antigenic specificity.
Widely used as therapeutic and diagnostic tools

Monoclonal Antibody Production

Mouse is challenged with antigen.
Spleen cells are harvested.
Hybridomas are created by fusing spleen cells with myeloma cells.
Hybridomas are cultured in HAT medium
Positive cells (producing monoclonal antibodies) are selected.
Monoclonal antibodies are harvested

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Description

Explore the fundamentals of antigen recognition in this quiz focused on B and T lymphocytes. Learn about the similarities, differences, and complexities of antibody classes and subclasses. This quiz is essential for understanding immune responses and the functions of lymphocytes.