Cannabinoid‐receptor expression in human leukocytes

Abstract

Marijuana and many of its constituent cannabinoids influence the central nervous system (CNS), probably through the cannabinoid receptor, which has recently been cloned in rat and human. While numerous reports have also described effects of cannabinoids on the immune system, the observation of both mRNA and cannabinoid receptor has hitherto been exclusively confined to the brain, a reported detection in the testis being the sole example of its presence at the periphery. Here we report the expression of the cannabinoid receptor on human immune tissues using a highly sensitive polymerase-chain-reaction-based method for mRNA quantification. We show that, although present in a much lower abundance than in brain, cannabinoid receptor transcripts are found in human spleen, tonsils and peripheral blood leukocytes. The distribution pattern displays important variations of the mRNA level for the cannabinoid receptor among the main human blood cell subpopulations. The rank order of mRNA levels in these cells is B cells > natural killer cells 2 polymorphonuclear neutrophils 2 T8 cells > monocytes > T4 cells. Cannabinoid-receptor mRNA, which is also found in monocytic, as well as T and B leukemia cell lines but not in Jurkat cells, presents a great diversity of expression on these cells as well, B-cell lines expressing a much higher level than T-cell lines. The cannabinoid receptor PCR products from leukocytes and brain are identical both in size and sequence suggesting a strong similarity between central and peripheral cannabinoid receptors. The expression of this receptor was demonstrated on membranes of the myelomonocytic U937 cells using the synthetic cannabinoid [3H]CP-55940 as ligand. The Kd determined from Scatchard analysis was 0.1 nM and the B,, for membranes was 525 fmol/mg protein. The demonstration of cannabinoid-receptor expression at both mRNA and protein levels on human leukocytes provides a molecular basis for cannabinoid action on these cells.

Distinct Expression Profiles of the Peripheral Cannabinoid Receptor in Lymphoid Tissues Depending on Receptor Activation Status

“…Dual immunohistochemistry using pan-B cell markers confirmed previous observations that in general B lymphocytes are the leukocyte subsets expressing CB2 mRNA and protein (3)(4)(5) (Fig. 4).…”

“…The mechanism of activation appears to be a different one, because we neither found any increase of the CB2 protein levels, nor did the CB2 receptor activation status change following CD40 stimulation (data not shown). The peripheral cannabinoid receptor belongs to the family of seven-transmembrane GPCRs (3,4). GPCRs are crucial to many cellular functions, such as proliferation, maturation, survival, apoptosis, or migration (10 -12); Carayon et al (5) showed moderate proliferation of virgin and GC tonsillar B cells upon stimulation with the synthetic cannabinoid agonist CP55,940 only when the cells were stimulated with CD40 mAbs.…”

“…The central cannabinoid receptor CB1 (1) is primarily expressed in brain, whereas the peripheral cannabinoid receptor CB2 (2) is mainly present in immune tissues. CB2 mRNA has been detected in human hemopoietic cells, with B cells expressing the highest transcript levels (3,4). In fact, using a polyclonal Ab raised against the C terminus of the human CB2 receptor, Carayon et al (5) demonstrated expression of the CB2 protein in the mantle zones (MZs) 3 of secondary follicles of tonsils.…”

“…CB2 mRNA has been detected in human hemopoietic cells, with B cells expressing the highest transcript levels (3,4). In fact, using a polyclonal Ab raised against the C terminus of the human CB2 receptor, Carayon et al (5) demonstrated expression of the CB2 protein in the mantle zones (MZs) 3 of secondary follicles of tonsils. These investigators reported that there was no CB2 staining on B lymphocytes in the germinal centers (GCs) of the secondary follicles.…”

Cannabinoids and neuroinflammation

“…CB 2 receptor activation typically inhibits the functions of immune cells (reviewed in Parolaro, 1999), likely via the known CB 2 receptor intracellular signaling mechanisms: inhibition of adenylyl cyclase activity by G i/o proteins and activation of mitogenactivated protein kinase (Bouaboula et al, 1993;Bayewitch et al, 1995;Felder et al, 1995;Wartmann et al, 1995). The following subsections discuss in more detail the effects of endogenous, plant, and synthetic cannabinoid compounds on peripheral immune cells.…”