Repeated administration of cannabidiol decreases splenic lymphocyte numbers in rats: involvement of CB ₂ receptors

Cannabidiol (CBD), the major non-psychotropic compound of Cannabis sp. , is an effective treatment for inflammatory and autoimmune diseases and produces various anti-tumor effects but the mechanisms of its long-term actions in vivo remain unclear. We have previously shown that CBD administration (5 mg/kg) in healthy rats significantly decreased lymphocyte numbers in peripheral blood, involving B, T CD4+ and T CD8+ lymphocyte subsets, but not natural killer (NK) cells. To examine the effects of CBD on lymphocyte subsets in the spleen and NK cellular cytotoxicity (NKCC), adult male Wistar rats (n = 63) were administered intraperitoneal injections of CBD (2.5 or 5 mg/kg/day) for 14 consecutive days and lymphocyte counts were obtained using flow cytometry. NKCC in the peripheral blood and spleen was quantified using a Chromium-51 release assay. Furthermore, CB ₂ receptors were blocked using selective receptor antagonist AM630 (1 mg/kg). The results indicate that repeated administration of CBD at a dose of 5 mg/kg/day resulted in a decrease in splenic lymphocyte number, involving T and B lymphocytes but not NK cells. The decrease in lymphocyte number was partially blocked by pretreatment with CB ₂ receptor antagonist while no changes in NKCC were observed following CBD administration. These results reveal that in healthy rats, CBD produces similar lymphopenic effects in the spleen as it does in peripheral blood and that the effects of CBD on lymphocyte numbers in vivo are at least partially mediated by CB ₂ receptors.