[Problems in the host defense system against bacterial infection]

Various types of defects in the host defense system are involved in bacterial infection especially in so-called compromised host. Among the humoral factors of defense system, complement system and immunoglobulins are indispensable. Phagocytes are the most important cellular factor in the effective phagocytosis and intracellular killing of ingested bacteria through the formation of ROI, RNI and by the release of antibacterial peptides including defensin or serprocidin family. T lymphocytes are specially required when the infection is caused by intracellular parasitic bacteria for activation of macrophages through the production of several cytokines or expression of cytotoxic effect. gamma delta T cell may be involved in the first line defense. The functional significance of each factor of host defense was discussed with special reference to the escape mechanisms of bacteria.