How does cannabis affect the immune system?

The immune system is extensively modulated by the ECS — CB2 receptors are highly expressed on immune cells (T cells, B cells, macrophages, NK cells, dendritic cells). THC and CBD have opposing immune effects in some contexts. THC: generally immunosuppressive — reduces T cell proliferation, shifts cytokine balance toward Th2 (anti-inflammatory), suppresses NK cell activity, and reduces macrophage function. This immunosuppression may be beneficial in autoimmune conditions but potentially harmful in infections or cancer immunosurveillance. CBD: more complex — anti-inflammatory via multiple pathways (COX inhibition, cytokine reduction) but less broadly immunosuppressive than THC. Clinical implications: (1) HIV patients: early concern that THC immunosuppression could accelerate disease — not confirmed in clinical studies. (2) Autoimmune disease: theoretical benefit from immunosuppression; limited clinical evidence. (3) Infection risk: chronic heavy use associated with increased respiratory infections. (4) Vaccine response: one study found reduced antibody response to hepatitis B vaccine in heavy cannabis users.