Studies on phagocytosis in patients with acute bacterial infections.

Polymorphonuclear leukocytes (PMN) and monocytes from 20 patients with acute bacterial infections were examined for phagocytic function. PMN of patients expressed markedly enhanced phagocytosis as measured by the ingestion of erythrocyte (E)IgG and IgG/C3b-coated E. Phagocytosis of E coated with C3b alone was not seen, while low levels of ingestion of iC3b-E by patients' PMNs was noted. Monocytes from patients and controls expressed similar phagocytic activity in a fixed endpoint assay; however, the kinetics of phagocytosis by patients' monocytes was strikingly faster. Superoxide anion (O2.) and myeloperoxidase activities were similar to controls in PMN of four patients studied on day 1 of admission. PMN from two of three patients studied longitudinally showed an initial elevation in EIgG phagocytosis, which fell to normal levels by day 4, concomitantly with increased O2. generation and clinical improvement. Phagocytosis remained elevated in the third patient who did not clear his septicemia. Surface membrane FcRII, FcRIII, CR1, and CR3 were similar on patient and control PMN. In contrast, FcRI was increased on PMN of five of seven patients by monomeric IgG binding, and on two of two patients by monoclonal anti-FcRI binding. Thus, PMN and monocytes of patients with acute bacterial infections are either upregulated with regard to phagocytic function or are less susceptible to downregulation than are normal cells. This presumably would have a beneficial effect on host defenses during infection.