Generation of Antibody Diversity

Abstract

Because of the huge diversity, the immunoglobulin repertoire cannot be encoded by static genes, which would explode the genomic capacity comprising about 20,000-25,000 human genes. The immunoglobulin repertoire is provided by the process of somatic germ line recombination, which is the only controlled alteration of the genomic DNA after meiosis. It takes place in mammalian B lymphocyte (B cells) precursors in the bone marrow. The genome germ line sequence of undeveloped B cells is organized in gene segments and compromise V (variable), D (diversity), and J (joining) gene segments constituting the variable domain of the heavy chain and only V and J genes for building up the variable domain of the light chain. The rearrangement of the variable region follows a strict order. The following processes that participate in the generation of antibody diversity were summarized-allelic, combinational, and junctional diversity, pairing of IgH and IgL, and receptor editing-which all together produce the primary antigen repertoire (pre-antigen stimulation). When a B cell encounters a foreign antigen, affinity maturation and class switch are induced. Thereby the antibody repertoire increases. The resulting secondary immunoglobulin repertoire reveals in humans at least 10 11 specificities for different antigens.