Lecture 5: Antigen Recognition by B Cell Receptors(based on Lecture by Dr. Matthew Scharff, Einstein)

Questions to Consider

How can we make antibody to every possible pathogen-i.e. Diversity?

How do we avoid making autoantibodies-i.e. Specificity?

How do we rapidly increase amount of antibody-i.e. Mobilization?

How do we switch from making IgM to IgG- i.e. Isotype Switching?

How do we increase the the affinity of antibody-i.e. Affinity maturation?

How do we generate memory?

Antibody Molecules Use Different Mechanisms to Prevent Infection

Antibody Levels and Affinity Are Increased by Immunization

Structure of the Antibody Molecule

Clonal Selection of Antigen- specific Lymphocytes

V Domains of Heavy and Light Chains Contain Discrete Hypervariable Regions

Hypervariable Regions Lie in Loops That Are Brought Together in the Folded Molecule

Clonal Selection of Antigen-specificLymphocytes

V-region Gene Are Constructed From Discrete Gene Segments

Germline Organization of the Immunoglobulin Heavy and Light-Chain Loci in the Human Genome

V-region Gene Segments Are Joined by Recombination

The Number of Functional Gene Segments for the V region Heavy and Light-Chains

Germline Organization of the Immunoglobulin Heavy and Light-Chain Loci in the Human Genome

Gene Segments Encoding the V Regions Are Flankedby Conserved Heptamer and Nonamer Sequences

Introduction of P- and N-nucleotides at the JointsBetween Gene Segments During Ig Gene Rearrangement

Contribution of Factors to Antigen Receptor Diversity

Clonal Selection of Antigen-specificLymphocytes

Neutralizing Antibodies Prevent Viral Infection of Cells

Somatic Mutation Increases Affinity

Abbas, Cellular and Molecular Immunology

centrocyteFDC

B Th

activation

centroblast Dark Zone

LightZone

selection

antigen

memory B cell plasma

B cell

apoptotic cell

anergic B cell

modified from Luo, Ronai, and Scharff. J Allergy Clin Immunol. 2004 and Harrison’s Principles of Internal Medicine 16th ed Ch. 97.

Pluripotent stem cell

Progenitor B cell

Pre-B cell

Immature B cell

mature B cell

SHMCSR

AID

AIDAID

Activation-inducedCytidine Deaminase (AID)

• AID is a cytidine deaminase whose in vitro substrate is ssDNA

• AID may associate with RPA, RNAP II &? others

• Transcription is required for somatic SHM and CSR

CUG

P182

CNESNLS

F15XR24W

H56Y

L59F

W68X

W80R

C87R

W84X

L106P

R112CR112H

M139VC147X

F151S

R174S R190X

L181

N alpha helix active site PS CSR

Deficiency causes Hyper IgM type II

Luo, Ronai, and Scharff. J Allergy Clin Immunol. 2004

AID deaminates C to U followed by UNG and APE1

J. Peled et al. Ann Rev Imm 2008

Somatic Hypermutation of Antibody V Regions

After Philip Coffino

10-1 10-3 10-6 10-9 10-11 MutationFrequency

Error pronePolymerases

High fidelityPolymerases

Proofreading Mismatch repair

healthcancercancerdeath

and yet alsofitness

Mutation Frequency = Mutations/bp/cell division

Biological consequence

Somatic Hypermutation

After T-cell-dependent Activation, B cells Undergo Rounds of Mutation and Selection That Generates High Affinity Memory B Cells

Janeway and Travers, Immunobiology

Somatic HypermutationLow affinity high affinity

Class Switch Recombination

IgM IgG / IgE / IgA

Effector arm

Antigen-binding site

Humoral Immune Response

Questions to Consider

How can we make antibody to every possible pathogen-i.e. Diversity

How do we avoid making autoantibodies-i.e. Specificity

How do we rapidly increase amount of antibody-i.e. Mobilization

How do we switch from making IgM to IgG- i.e. Isotype Switching

How do we increase the the affinity of antibody-i.e. Affinity maturation

How do we generate memory