Immunoglobulin genes

The mu (µ) and delta (δ) C genes are those nearest to the assembled VDJ sequence. Transcription of a complete immunoglobulin heavy chain gene starts at the V sequence and proceeds through the mu (µ) and delta (δ) sequences before terminating. The mature B cell expresses both IgM and IgD, which are the only isotypes produced by B lymphocytes prior to contact with antigen.