Immunoglobulin heavy chain

[3] There are five types of mammalian immunoglobulin heavy chain: γ, δ, α, μ and ε.

Each heavy chain has two regions: Cows, specifically Bos taurus, show a variation on the general mammalian theme in which the heavy chain CDR H3 region has adapted to produce a divergent repertoire of antibodies which present a "stalk and knob" antigen interaction surface instead of the more familiar bivalent tip surface.

[7] The bovine CDR is unusually long and contains unique sequence attributes which support the production of paired cysteine residues during somatic hypermutation.

[7] A speculated evolutionary driver for this variation is the presence of a vastly more diverse microbial environment in the digestive system of the cow as a consequence of their being ruminants.

The resulting antibodies are designated IgW (also called IgX or IgNARC) and IgNAR (immunoglobulin new antigen receptor).

Schematic diagram of a typical antibody showing two Ig heavy chains (purple) joined by disulfide bonds to two Ig light chains (green). The constant (C) and variable (V) domains are shown.
An antibody molecule. The two heavy chains are colored red and blue and the two light chains green and yellow. [ 1 ]