FIG. 1.

In vivo uptake of S. pyogenes by peritoneal macrophages. Mice were intraperitoneally inoculated with either 10⁷ (A), 5 × 10⁷ (B), or 10⁸ (C) CFU of green-labeled S. pyogenes (solid histograms) or PBS (open histograms) and subjected to peritoneal lavage, and peritoneal macrophages were labeled with PE-conjugated anti-F4/80 antibodies. Flow cytometry analysis was performed by gating the F4/80⁺ population, and the association of green-labeled streptococci with macrophages was expressed as the increase in green fluorescence of macrophages (FL-1). One representative experiment out of three is shown.