Phagocytosis by human alveolar macrophages and neutrophils: qualitative differences in the opsonic requirements for uptake of Staphylococcus aureus and Streptococcus pneumoniae in vitro

Abstract

The opsonic requirements for uptake of 3H-adenine-labeled Staphylococcus aureus (strains 502A, Wood 46, or 209) or Streptococcus pneumoniae (Type VII) by human alveolar macrophages (AM) or neutrophils (PMN) were evaluated and compared using a quantitative assay of phagocytosis. AM readily engulfed S. aureus organisms preopsonized with 1% albumin, serum, or serum that had been heated (56 degrees C for 30 min) to inactivate complement, whereas uptake of S. aureus by PMN occurred only after preopsonization with unheated, complement replete serum (2.5%). In contrast, uptake of S. pneumoniae organisms by AM or PMN did not occur with only albumin preopsonization, but required high concentrations (more than 40%) of unheated serum. The results indicate that there are qualitative and quantitative differences in the requirements for optimal ingestion of bacteria by human AM or PMN that relate not only to the type of organism but also to the type of phagocyte. Variations in opsonic requirements may be a key factor in the different cellular responses and clearances of inhaled S. aureus or S. pneumoniae organisms by the lungs.