Ig delta chain C region is an allelic product of the human IGHD gene. The two known IGHD alleles, IGHD*01 and IGHD*02, respectively produce isoforms 1, a secreted protein, and 2, a single-pass type I membrane protein. A member of the adaptive immune system, IgD antibodies are monomers expressed by activated B cells. Containing 3 Ig-like (immunoglobulin-like) domains, IgD chain C is located on chromosome 14 within the human heavy chain locus, lying on the 3’ side of the IgM chain C region from the V-D-J cassette. Polyadenylation at certain sites along the heavy chain locus likely effects the mechanism that determines the alternative splicing event which results in the expression of either IgD chain C or IgM chain C. Some studies have suggested that antigenic coactivation of IgD+ B cells can have a negative influence on bone resorption during infectious events.