mRNA encoding for the CB2 cannabinoid receptor is expressed by many subsets of human peripheral blood leukocytes (PBL), but little is known about the resulting protein expression and function. Employing clones from the A549 and 293T cell lines that were constructed to express both full-length human CB2 and GFP, we developed a flow cytometry assay for characterizing CB2 protein expression. A monoclonal antibody directed against human CB2 selectively stained the surface of transduced but not parental cell lines. When cells were fixed and permeabilized, imaging flow cytometry identified large stores of intracellular protein. Total cellular staining for CB2 corresponded closely with the level of GFP expression. When exposed to Δ-9-tetrahydrocannabinol, CB2-expressing cells internalized cell surface CB2 receptors in a time- and dose-dependent manner. Applying these approaches to human PBL, CB2 protein was identified on the surface of human B cells but not on T cells or monocytes. In contrast, when PBL were fixed and permeabilized, intracellular CB2 expression was readily detected in all three subsets by both conventional and imaging flow cytometry. Similar to the protein expression pattern observed in fixed and permeabilized PBL, purified B cells, T cells, and monocytes expressed relatively equal levels of CB2 mRNA by quantitative real-time RT-PCR. Our findings confirm that human PBL express CB2 protein but that its distribution is predominantly intracellular with only B cells expressing CB2 protein at the extracellular membrane. The differential role of intracellular and extracellular CB2 receptors in mediating ligand signaling and immune function remains to be determined.

The capacity for human monocytes to differentiate into antigen-presenting dendritic cells (DC) can be influenced by a number of immune modulating signals. Monocytes express intracellular cannabinoid type 1 (CB1) and 2 (CB2) receptors and we demonstrate that exposure to Δ9-tetrahydrocannabinol (THC) inhibits the forskolin-induced generation of cyclic adenosine monophosphate in a CB2-specific manner. In order to examine the potential impact of cannabinoids on the generation of monocyte-derived DC, monocytes were cultured in vitro with differentiation medium alone [containing granulocyte/macrophage-colony stimulating factor (GM-CSF) and Interleukin-4 (IL-4)] or in combination with THC. The presence of THC (0.25–1.0 μg/ml) altered key features of DC differentiation, producing a concentration-dependent decrease in surface expression of CD11c, HLA-DR and costimulatory molecules (CD40 and CD86), less effective antigen uptake, and signs of functional skewing with decreased production of IL-12 but normal levels of IL-10. When examined in a mixed leukocyte reaction, DC that had been generated in the presence of THC were poor T cell activators as evidenced by their inability to generate effector/memory T cells or to stimulate robust IFN-γ responses. Some of these effects were partially restored by exposure to exogenous IL-7 and bacterial superantigen (S. aureus Cowans strain). These studies demonstrate that human monocytes express functional cannabinoid receptors and suggest that exposure to THC can alter their differentiation into functional antigen presenting cells; an effect that may be counter-balanced by the presence of other immunoregulatory factors. The impact of cannabinoids on adaptive immune responses in individuals with frequent drug exposure remains to be determined.

Cannabinoid receptor type 2 (CB2) is the primary receptor pathway mediating the immunologic consequences of cannabinoids. We recently reported that human peripheral blood B cells express CB2 on both the extracellular membrane and at intracellular sites, where-as monocytes and T cells only express intracellular CB2. To better understand the pattern of CB2 expression by human B cells, we examined CD20+ B cells from three tissue sources. Both surface and intracellular expression were present and uniform in cord blood B cells, where all cells exhibited a naïve mature phenotype (IgD+/CD38Dim). While naïve mature and quiescent memory B cells (IgD−/CD38−) from tonsils and peripheral blood exhibited a similar pattern, tonsillar activated B cells (IgD−/CD38+) expressed little to no surface CB2. We hypothesized that regulation of the surface CB2 receptor may occur during B cell activation. Consistent with this, a B cell lymphoma cell line known to exhibit an activated phenotype (SUDHL-4) was found to lack cell surface CB2 but express intracellular CB2. Furthermore, in vitro activation of human cord blood resulted in a down-regulation of surface CB2 on those B cells acquiring the activated phenotype but not on those retaining IgD expression. Using a CB2 expressing cell line (293T/CB2-GFP), confocal microscopy confirmed the presence of both cell surface expression and multifocal intracellular expression, the latter of which co-localized with endoplasmic reticulum but not with mitochondria, lysosomes, or nucleus. Our findings suggest a dynamic multi-compartment expression pattern for CB2 in B cells that is specifically modulated during the course of B cell activation.

Bisphenol A (BPA) is an organic compound commonly used in the production of plastics and plastic additives. BPA is an endocrine disruptor that can mimic hormones, including estrogen, and can cause severe health problems. Studies have consistently shown an association with BPA urine concentrations and heart disease. It has been well documented that estrogen has cardioprotective effects. Therefore, it is seemingly contradictory that BPA, which activates the estrogen receptor, would be detrimental to the heart. In order to gain greater insight into the biochemical response to BPA in comparison to estrogen, we characterized miRNA signatures in cardiomyocytes of miRNAs previously documented to influence cardiovascular disease. Following treatment of primary neonatal rat cardiomyocyte cultures with either estradiol or BPA, miRNAs levels were analyzed by Taqman Real‐Time PCR. Exposure to BPA did produce a unique miRNA signature as compared to exposure to estradiol.