Leukocyte phagocytic function and dysfunction.

Although some species of bacteria are killed in vitro by humoral factors in cell-free serum, the in vivo experience with leukopenic patients illustrates the critical role played by phagocytic leukocytes in host resistance to infection. Effective ingestion and killing of micro-organisms requires the sequential and integrated function of the elements of the phagocytic system. Each step in the phagocytic process is also a potential crack in the armor of host defense, and an increasing number of clinically significant disorders of phagocytic function are being recognized and described (5). The phagocytic leukocytes are equipped with a variety of intracellular microbicidal mechanisms which provide a degree of overkill capacity and allow these cells to meet the challenges posed by the many and varied microbial transfressors. Undoubtedly, other phagocytic disorders will be discovered and other important aspects of the intraleukocyte killing mechanisms will be elucidated. For instance, little is known about the function of leukocytes within the relatively hypoxic environment of injured tissue where so many bacterial infections begin. As our understanding of phagocytic function develops, new ways may be found to augment host resistance by preservation or stimulation of the phagocytes.