Phagocytosis, bacterial killing, and metabolism by purified human lung phagocytes

Phagocytic and bactericidal activities of purified polymorphonuclear neutrophils (PMNs), monocytes (MNs), or alveolar macrophages (AMs) from the same individuals for Staphylococcus aureus strain 502A or Escherichia coli strain ON2 were compared in vitro. Factors that may influence these activities were evaluated. The bactericidal activity of S. aureus and E. coli of PMNs was greater than that of MNs or AMs. Two factors were identified that may account for this result. (1) The rate of phagocytosis of opsonized S. aureus and E. coli was greater by PMNs. (2) The nonmitochondrial oxygen burst after nonparticulate stimulation was much greater by PMNs. Qualitative differences in opsonic requirements for ingestion of S. aureus by PMNs, MNs, and AMs were also identified. In contrast to PMNs or MNs, phagocytosis of S. aureus by AMs was not opsonin-dependent. The results suggest that mononuclear phagocytes may adapt their opsonic requirements to facilitate uptake of S. aureus. Despite this adaptation, their bactericidal capability remains limited when compared with PMNs.