[Specific and non-specific defense mechanisms against infection].

Defense mechanisms against bacterial, viral or parasitic infections require the cooperation of effector cells (mainly polymorphonuclear and mononuclear phagocytes) and mediators such as antibodies, complement and lymphokines. Antibodies and some complement components promote the endocytosis of microorganisms whereas lymphokines activate phagocytic cells. Once endocytosed, microorganisms are killed either by oxidative reactions consequent to the respiratory burst, or by the particular conditions and factors that they encounter in phagolysosomes. Intact microorganisms or their degradation products handled by mononuclear phagocytes represent immunogenic moieties which can trigger immunocompetent lymphocytes and induce specific immune responses. Phagocytic cells may have characteristic intrinsic deficiencies that are responsible for prolonged or recurrent infections.