Quantitative method to determine mRNA levels by reverse transcriptase-polymerase chain reaction from leukocyte subsets purified by fluorescence-activated cell sorting: application to peripheral cannabinoid receptors

Identification of transcription start sites and preferential expression of select CB2 transcripts in mouse and human B lymphocytes

Marijuana cannabinoids, the endocannabinoids, and cannabinoid cell receptors have been shown to play important roles in immune regulation particularly as potent modulators of anti-inflammatory cytokines. The predominant cannabinoid receptor involved in this immune regulation is cannabinoid receptor 2 (CB(2)), which is predominantly expressed in B lymphocytes. However, the promoter region and mechanisms of CB(2) gene regulation are unknown in this immune cell type. Utilizing a combination of bioinformatics, 5' rapid amplification of cDNA ends (5' RACE), real-time reverse transcription-polymerase chain reaction, DNA sequencing, and luciferase reporter assays, we show that human B cells express one CB(2) transcript while mouse B cells express three CB(2) transcripts, with specific transcript selection occurring during B cell activation by lipopolysaccharide. Alignment of our sequenced RACE products to either the mouse or human genome, along with the GenBank submitted mRNA sequences, revealed that the transcripts we isolated contained previously unidentified transcriptional start sites (TSS). In addition, expression construct testing of the genomic region containing the TSSs of the mouse CB(2) exon 1 transcripts showed an eightfold increase of promoter activity over baseline. These data show for the first time that human B cells use only one TSS for CB(2) while mouse B cells use multiple TSSs and that the mouse TSSs are in a genomic area with promoter activity, thus suggesting the location of the gene promoter region. Defining these TSSs also provides clues to the various gene regulatory factors involved in the expression of CB(2) during B cell activation.

Effects of delta-9-tetrahydrocannabinol on human immune function and host defense

This review examines evidence that delta(9)-tetrahydrocannabinol (THC) can regulate and suppress human immune responses. Leukocytes express both cannabinoid receptor type 1 (CB1) and cannabinoid receptor type 2 (CB2), and levels of mRNA encoding for them are increased in peripheral blood leukocytes obtained from marijuana smokers, suggesting cannabinoid receptor activation in vivo. Exposure of human T-cells to THC suppresses their proliferation, inhibits the release of interferon-gamma, and skews the balance of T-helper cytokines towards a type 2 response. The majority of these effects are CB2 receptor-dependent. Consistent with an impact of THC on cell-mediated immunity, alveolar macrophages (AMs) recovered from the lungs of marijuana smokers are suppressed in their ability to release pro-inflammatory cytokines and nitric oxide (NO), and kill bacteria. Macrophage function is restored by treatment with interferon-gamma, a type 1 cytokine. Habitual exposure to THC appears capable of impacting on human cell-mediated immunity and host defense.

Delta 9-Tetrahydrocannabinol regulates Th1/Th2 cytokine balance in activated human T cells

Human leukocytes express cannabinoid (CB) receptors, suggesting a role for both endogenous ligands and Delta 9-tetrahydrocannabinol (THC) as immune modulators. To evaluate this, human T cells were stimulated with allogeneic dendritic cells (DC) in the presence or absence of THC (0.625-5 microg/ml). THC suppressed T cell proliferation, inhibited the production of interferon-gamma and shifted the balance of T helper 1 (Th1)/T helper 2 (Th2) cytokines. Intracellular cytokine staining demonstrated that THC reduced both the percentage and mean fluorescence intensity of activated T cells capable of producing interferon-gamma, with variable effects on the number of T cells capable of producing interleukin-4. Exposure to THC also decreased steady-state levels of mRNA encoding for Th1 cytokines, while increasing mRNA levels for Th2 cytokines. The CB2 receptor antagonist, SR144528, abrogated the majority of these effects. We conclude that cannabinoids have the potential to regulate the activation and balance of human Th1/Th2 cells by a CB2 receptor-dependent pathway.

Altered cannabinoid receptor mRNA expression in peripheral blood mononuclear cells from marijuana smokers

We studied, using RT-PCR, the relative expression of cannabinoid receptor (CBR) mRNA in peripheral blood mononuclear cells (PBMC) from different donor groups. Cells from normal donors expressed a CB2 mRNA level threefold higher than CB1 across all age, gender or ethnicity groups, and amplicons were of the same size in all donors. However, cells from marijuana users expressed higher levels of CBR mRNA, but with a preserved CB1/CB2 ratio of 1:3. CBR gene products were also studied following short-term mitogen activation in vitro. CB1 expression decreased following mitogen stimulation when compared to the time-matched medium only cells while the expression of CB2 mRNA remained unchanged. These studies suggest that marijuana smoking and immune activation can alter the basal levels of CB1 and CB2 in PBMCs.

Genomic and functional changes induced by the activation of the peripheral cannabinoid receptor CB2 in the promyelocytic cells HL-60. Possible involvement of the CB2 receptor in cell differentiation

The function of the peripheral cannabinoid receptor (CB2), which is mainly expressed on hematopoietic cells, remains an enigma. In an attempt to decipher its role, we used Affymetrix DNA chips to investigate the gene expression profile of the promyelocytic cells HL-60 transfected with the CB2 receptor and activated with the cannabinoid agonist CP 55,940. Agonist exposure of these cells led to an activation of a mitogen-activated protein kinase cascade and a receptor desensitization, indicating a functional coupling of the transfected receptors. At the genomic level, activation of the CB2 receptors induced an up-regulation of nine genes involved in cytokine synthesis, regulation of transcription, and cell differentiation. A majority of them are under the control of the transcription factor NF-kappaB, whose nuclear translocation was demonstrated. Many features of the transcriptional events, reported here for the first time, appeared to be related to an activation of a cell differentiation program, suggesting that CB2 receptors could play a role in the initialization of cell maturation. Moreover, we showed that CB2-activated wild-type HL-60 cells developed properties usually found in host defense effector cells such as an enhanced release of chemotactic cytokines and an increased motility, characteristic of more mature cells of the granulocytic-monocytic lineage.

The neuroprotective agent SR 57746A abrogates experimental autoimmune encephalomyelitis and impairs associated blood-brain barrier disruption: implications for multiple sclerosis treatment

Experimental autoimmune encephalomyelitis (EAE) is a T cell autoimmune disorder that is a widely used animal model for multiple sclerosis (MS) and, as in MS, clinical signs of EAE are associated with blood-brain barrier (BBB) disruption. SR 57746A, a nonpeptide drug without classical immunosuppressive properties, efficiently protected the BBB and impaired intrathecal IgG synthesis (two conventional markers of MS exacerbation) and consequently suppressed EAE clinical signs. This compound inhibited EAE-induced spinal cord mononuclear cell invasion and normalized tumor necrosis factor alpha and IFN-gamma mRNA expression within the spinal cord. These data suggested that pharmacological intervention aimed at inhibiting proinflammatory cytokine expression within the central nervous system provided protection against BBB disruption, the first clinical sign of EAE and probably the key point of acute MS attacks. This finding could lead to the development of a new class of compounds for oral therapy of MS, as a supplement to immunosuppressive agents.