Question

Your body can defend you from any antigen that enters your body as long as that antigen is a foreign antigen.

How can your body generate such a diverse variety of antibodies? (2) Hint V and J chains

Answer 1

Antibodies are encoded by different germ-line genetic loci. Variable (V) region, joining (J) region, and constant (C) region gene products are assembled into a functional antibody.

Variable portion genes (V) code for amino acids that constitute the framework regions of the variable region, and three hypervariable complementarity-determining regions. These three regions are CDR1, CDR2, and CDR3. The hypervariable regions form three-dimensional antigen-binding pocket. Antibody specificity is determined by the specific amino acid sequences in CDR3. The joining (J) segment is a part of the V region and provides certain framework for the antigen-binding site. Heavy chains have an additional diversity (D) gene.

Antibody diversity is generated from the large number of V, J, D, and C genes available for recombination. Light-chain loci have 30 to 35 genes encoding for the variable (VL) regions. Five to seven genes code for JL segments in kappa (κ) or lambda (λ) light chains, respectively. Lambda and kappa light chains have one highly conserved constant region.

Heavy chains are larger than the light chains. A hundred genes code for heavy-chain variable (VH) regions. Diversity (D) genes are inserted between V and J genes.

The constant region may be from one of the five antibody isotypes -

IgM-mu [μ]

IgG- gamma [γ],

IgA- alpha [α],

IgE- epsilon [ε], or

IgD- delta [δ]). An assembled heavy chain consists of VJDC gene products.