Taken from Jean-Claude Weill, and Claude-Agnes Reynaud. 2008. DNA polymerases in adaptive immunity. Nature Reviews Immunology. 8: 302-312. After gene rearrangement (V(D)J recombination) antibody DNA can be further modified and diversified by three mechanisms:
- somatic hypermutation (initiated by AID, occurs during B cell proliferation in germinal centers, happens in humans, largely a random process, associated with class switching, affinity maturation [where Ab acquires better binding ability to antigen over time], happens in CDRs [complementariy-determining region] more frequently than framework and J segments, mutation rate is 100 000x higher than in other genes)
- gene conversion (occurs after gene rearrangement, only one functional V and J region in chickens, pseudogene elements largely incorporated into V region)
- class switch recombination (enables production of different classes of antibodies: IgG1-4, IgA, IgM, IgD, IgE, in order of decreasing quantity found in blood in humans. In chickens, homologs of IgG, IgM and IgA are present, in order of decreasing serum concentrations in blood)
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