Role of T- and B-lymphocytes in pulmonary host defences.

Pulmonary infectious diseases cause significant morbidity and mortality in both industrialized and developing countries. Adaptive immune responses are required to defend the lung against pathogens that survive in normal macrophages and extracellular organisms that evade phagocytosis. Microbes initiate both innate immune responses and specific adaptive immune responses. Innate immune response molecules regulate T-lymphocyte differentiation. Activated T-lymphocytes provide cytokines, which activate macrophages and lytic signals that lyse infected antigen-presenting cells. Antibodies produced by plasma cells facilitate microbial clearance through diverse effector mechanisms including opsonization, complement fixation and antibody-dependent cytotoxicity. Lymphocytes determine the specificity of the immune response and orchestrate effector limbs of the immune response.