IgD

Immunoglobulin D (IgD) is an antibody class which in the humoral, specific arm of Immunity. It's main function is as an antigen receptor on B lymphocytes. Because of this, it has very low serum concentrations. IgD and IgM are the only 2 Immunoglobins that are co-expressed.

It is roughly 185 kD in molecular weight and has 4 domains; 2 δ heavy chains and 2 light chains.