Drugs of abuse and virus susceptibility.

It is widely recognized that various microorganisms including viruses have immunomodulatory effects and, under appropriate circumstances, may markedly suppress the immune response mechanisms. Cannabinoids present in marijuana also have immunomodulatory effects. In the present studies THC as well as its metabolic product 11-OH THC were studied in regard to their effects in vivo and in vitro on selected parameters of the immune response system known to be important in antiviral resistance, including immunity to retroviruses. Cannabinoids markedly suppressed the ability of murine macrophages to spread on glass (an important functional marker of macrophages) as well as to phagocytize yeast particles. Splenic macrophage cultures treated with the cannabinoids also were deficient in their ability to produce interleukin 1 on appropriate stimulation with bacterial LPS. Spleen cells capable of producing antibody to sheep erythrocytes when stimulated with this antigen in vitro were markedly affected when treated with graded doses of THC or 11-OH THC. Furthermore, the blastogenic responsiveness of normal mouse splenocytes to the T-cell mitogens Con A and PHA as well as the B-cell mitogen E. coli LPS was markedly suppressed by graded concentrations of the cannabinoids in doses that did not affect the viability of the cells. Natural killer cell activity of normal mouse spleen cells was also markedly inhibited by THC and 11-OH THC. Similarly, these cannabinoids suppressed the blastogenic responsiveness and NK activity of human peripheral blood leukocytes from normal individuals. The ability of mouse spleen cells to produce interferon on in vitro stimulation was also suppressed by THC. In addition, injection of THC into mice suppressed blastogenic responsiveness of spleen cells, NK activity, and the production of interferon by lymphoid cells. Thus, it was apparent that these cannabinoids had immunomodulatory effects, both in vivo and in vitro, at noncytotoxic small doses and impaired the ability of the lymphoid cells to express immune function necessary for antiviral resistance.