Cell Mediated Immunity in Human Pathology: The Importance of Choosing the Right Weapon

ent pathogens; these mechanisms are mainly secondary to the activation of B lymphocytes and of humoral immunity, or to the activation of cell-mediated immunity. Activation of B lymphocytes, and production of antibodies has been shown to be more useful in defense against cell-free agents and toxins (e.g., pneumococcus; tetanus toxins). In contrast, triggering of cell-mediated immunity appears to be effective against infections by cell-associated pathogens and parasites (e.g., leishmania; mycobacteria; toxoplasma; treponema; HIV). 1’2 The mechanisms that regulate the induction of humoral and cell mediated immunity have been clarified by the identification in mice and man of two functionally distinct T helper lymphocyte compartments defined as T helper (TH1) and T helper 2 (TH2). TH1 lymphocytes secrete interferon gamma (IFNy) and interleukin (IL)-2 and mainly promote cell mediated immunity; TH2 lymphocytes