F-actin and p57 colocalize on forming phagosomes containing OpZ. (A) F-actin and p57 are enriched on forming OpZ phagosomes. Adherent PMNs ingested OpZ for 0.5 minutes or 7 minutes at 37°C before processing for IFM. Samples were double-stained with rhodamine-phalloidin to visualize F-actin and MoAbs to p57 as described above. p57 and F-actin were enriched on early phagosomes (upper panels), but not late phagosomes (arrowheads, lower panels). Neither marker was detected on uningested OpZ (arrow, upper panels). (B) Kinetics of F-actin and p57 association with OpZ. Adherent PMNs ingested OpZ for 0 to 15 minutes at 37°C before processing for IFM. F-actin and p57 were detected as in (A). Data shown are the mean ± SD of six to seven independent experiments. For each time point, 100 phagosomes/sample were scored. (•), F-actin; (○), p57.