Organization and Reorganization of Immunoglobulin Heavy-chain Genes

Each of the immunoglobulin polypeptides, light (L) and heavy (H) chains, comprises an aminoterminal variable (V) region, which determines antigen-binding specificity, and a carboxyterminal constant (C) region, which mediates biological effector functions. Immuno- globulins can be divided into five major classes, IgM, IgG, IgA, IgD, and IgE, which are defined by their heavy-chain constituents, μ, γ, α, δ, and ε, respectively.