Which class of immunoglobulin possesses delta heavy chains?

• A. IgA
• B. IgD
• C. IgE
• D. IgG

Answer: (B)

Delta heavy chains define the IgD class. Each immunoglobulin class uses a distinct heavy-chain isotype: mu for IgM, delta for IgD, gamma for IgG, alpha for IgA, and epsilon for IgE. IgD is mainly expressed on the surface of naive B cells as part of the B cell receptor, usually co-expressed with IgM due to alternative splicing of the heavy-chain transcript. This arrangement allows the B cell to recognize antigen with a single specificity while preparing for activation. IgD’s role is less about circulating antibodies and more about initiating B cell signaling and maturation. So, the class that possesses delta heavy chains is IgD.