Don't know if this helps, but...

Tetrahydrocannabinol (THC) is the major active component of cannabis, or marijuana. Receptors to THC have been found on B cells, natural killer cells, neutrophils, monocytes, lymphocytes and macrophages (Life Sci 1999; 65:637-644). Marijuana has measurable in vitro effects on the immune system, particularly in reducing cell-mediated immunity, which might increase susceptibility to infection. Clinical studies in humans so far, though, haven't demonstrated that these effects are clinically relevant (J Allergy Clin Immunol 1976;58:483-490). Chronic smoking of marijuana, however, can raise one's susceptibility to respiratory infection and cancer (Cancer Epidemiol Biomarkers Prev. 1999;8:1071-1078). If the marijuana is contaminated with mould spores, which is common, smoking it may lead to allergic asthma, infection or hypersensitivity pneumonitis (J Allergy Clin Immunol 1983;71:389-393)