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 kDa in molecular weight and has 4 domains; 2 δ heavy chains and 2 light chains.

B lymphocytes that co-express IgD and IgM have not undergone class switching. As a result a long mRNA transcript is produced which, when spliced can produce either of the mRNA molecules responsible for producing IgD or IgM depending where the cuts are made.