Abstract
Lung macrophages phagocytose unopsonized particles and pathogens via innate immune receptors such as scavenger receptors (SR). Signaling pathways for SR‐mediated phagocytosis of unopsonized bacteria likely govern the fate of ingested pathogens, but are poorly characterized. To allow high‐throughput screening (HTS) analysis, we developed a scanning cytometry assay to quantify phagocytosis of S. aureus by adherent human AM‐like macrophages. We compared the effects of receptor, signaling and cell process inhibitors (n = 7) on phagocytosis by human blood‐derived macrophages of a panel of live unopsonized S. aureus strains, (Wood, ATCC 29523, RN6390), as well as killed Wood strain, and latex beads. Differential fluorescent labeling of internalized vs. bound bacteria and image analysis of collapsed stacks of confocal sections in triplicate wells provided quantitation for ~500 cells per inhibitor per sample from three normal individuals. We found surprising heterogeneity of inhibition patterns among S. aureus strains, as well as between live and killed Wood strain, and between all S. aureus forms and unopsonized latex beads. The classic antagonist of SRs polyinosine inhibited uptake of latex beads and killed Wood strain, but had no effect on uptake of any live S. aureus strains. The data confirm the utility of the HTS assay, and suggest that receptor(s) other than SRs mediate uptake of live unopsonized S. aureus.Supported by NIH ESO11008 and ESO11903
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