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The role of alternative complement pathway activation in protection against infection is not well understood. We have investigated nonspecific opsonic activity in human adult, term neonatal and premature serum using the technique of neutrophil chemiluminescence (CL) to measure particle uptake. Following phagocytosis, neutrophils become metabolically active, produce excited molecular oxygen and emit a burst of light which can be detected and quantitated in a liquid scintillation counter. In the present study, zymosan particles were preopsonized in human serum and added to control neutrophils. Particles opsonized in adult serum produced a marked peak in CL. Serial dilutions of the serum prior to opsonization yielded proportionally lower peaks in CL. Opsonic activity as measured by the CL procedure was completely blocked by the addition of chelating agents which remove calcium and magnesium ions and block both classic and alternative complement pathway activation. Addition of an excess of magnesium ions (needed for alternative pathway activation) to the reaction mixture partially restored the opsonic activity. Opsonic activity as measured by the CL procedure was significantly depressed in approximately two-thirds of term and premature infant sera tested. Deficient nonspecific opsonic activity was closely correlated with serum levels of C3PA. These studies suggest that the CL procedure may be of value in the investigation of nonspecific opsonins in human serum.

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A B S T R A C T To determine if changes in neutrophil leukocyte function occur during active bacterial infection, the neutrophils of 25 patients with active bacterial infection and 25 age-matched controls were compared for leukotactic activity, random mobility, and nitroblue tetrazolium reduction. The neutrophil leukocytes of patients with bacterial infection were hyperactive in unidirectional movement toward a chemotactic stimulus as measured in the leukotactic assay and usually had increased nitroblue tetrazolium reduction. The mean leukotactic index was 165±+56 in patients with bacterial infection and 70±11 in controls (P<0.001). After 7-10 days of appropriate therapy with clinical and bacteriological response, leukotactic activity returned to normal values. A hyperactive leukotactic response continued, however, in patients with persisting bacterial infection. The hyperactive leukotactic response of circulating neutrophils appears to be an early and sensitive event in the inflammatory cycle stimulated by bacterial infection and may aid in the localization of invading bacteria.