Distinct expression profiles of the peripheral cannabinoid receptor in lymphoid tissues depending on receptor activation status.

Using two distinct anti-CB2 receptor Abs, we investigated the expression patterns of the peripheral cannabinoid receptor CB2 in human secondary lymphoid organs. Immunohistochemical analysis using an N-terminal specific anti-CB2 Ab revealed high protein expression in the germinal centers (GCs) of secondary follicles. A C-terminal specific anti-CB2 Ab, which only recognizes a nonphosphorylated inactive receptor, showed positivity in the mantle zones (MZs) and marginal zones (MGZs) of the secondary follicles where resting cells reside, and in the primary follicles. In contrast, no positivity was observed in GCs using the C-terminal Ab, suggesting that active CB2 receptors are mainly present on cells in the GCs. Dual immunohistochemical analysis revealed that B lymphocytes express the CB2 protein abundantly. In contrast to B cells in the MZ or MGZ, CB2-expressing cells in the GCs coexpress the costimulatory membrane protein CD40, which is mainly expressed in the GCs and at very low levels in the MZs and MGZs and the proliferation marker Ki-67. Using the human Raji B cell line as a model, we demonstrate in a transwell assay that moderate migration occurs upon stimulation of the CB2 receptor with the endocannabinoid 2-arachidonoylglycerol, which is enhanced by CD40 costimulation. Our findings, that GC-related cells express active CB2 and that CB2-dependent migration requires CD40 costimulation, suggest that CB2 is involved in B cell activation.