Cannabinoid receptor 2 (CB2) is expressed in B lymphocytes and is involved in immune regulation. Mouse splenic B cells express three CB2 transcripts utilizing two different first exons. Human peripheral blood B cells express one CB2 transcript utilizing one first exon. Alignment of sequenced RACE products to either the mouse or human genome reveals that isolated transcripts contain previously unidentified transcriptional start sites (TSS). B cells from mouse and human preferentially express one transcript, exon 1a in mouse and exon 1 in human. Multiple CB2 TSSs are utilized in mouse splenic B cells and one TSS in human peripheral blood B cells. The defining of the receptor gene TSSs in these cells provides materials and methods for therapeutically regulating immune function, including antibody isotype switching, using compounds such as inhibitory nucleic acids that down-regulate expression of the B cell CB2 gene (e.g., RNAi molecules).