Cannabinoids and cannabinoid receptors have been shown to play important roles in immune regulation particularly as modulators of anti-inflammatory cytokines and antibody production. The predominant cannabinoid receptor involved in this immune regulation is cannabinoid receptor 2 (CB2), which is robustly expressed in B cells. Utilizing a combination of bioinformatics, 5' RACE, real time RT-qPCR, and reporter assays, we showed that human B cells from peripheral blood mononuclear cells (PBMC) expressed one CB2 transcript while mouse B cells from spleen express three CB2 transcripts. Alignment of the sequenced B cell RACE products to either the mouse or human genome, along with the GenBank mRNA sequences, revealed that the transcripts isolated in this study contained previously unidentified transcriptional start sites (TSSs). In addition, expression construct testing of the genomic region containing the TSSs of the mouse CB2 exon 1 and 2 transcripts showed a significant increase of promoter activity. Bioinformatics analysis for cis-sequences in the promoter regions identified DNA binding sites for NF-kB, STAT6, and Elk1 transcription factors activated by LPS, IL-4 and anti-CD40. Regarding variations in CB2 transcript expression among the immune cell subtypes, RACE analysis showed that the exon 1b transcript is seen in B cells but not in T cells, dendritic cells or macrophages. Furthermore, RT-qPCR showed variations in transcript expression during B cell development as well as in resting versus LPS or IL-4/anti-CD40 stimulated B cells. The exon 1a transcript was predominant in pre-, immature and resting B cells whereas the exon 1b and 2 transcripts were enhanced in mature and activated B cells. These data showed for the first time that human B cells use one TSS for CB2 expression while mouse B cells use multiple TSSs for the expression of three CB2 transcripts, in which the expression of the individual transcript is related to immune cell type and/or cell activation state. Additionally, this is the first report in mouse B cells defining TSSs that are in genomic areas with promoter activity thus suggesting the location of two promoter regions. Defining the CB2 transcript expression during various stages of B cell activation provide clues to therapeutic methods.