FIG. 3.

Specific blocking of Fc receptors on J774A.1 cells abrogates the inhibition of YopH delivery by anti-LcrV antibody. Panel A: control test for efficacy of FcBlock in inhibiting phagocytosis mediated by IgG1. J774A.1 cells were treated with Fc Block or PBS for 1 h and then allowed to engulf opsonized fluorescent beads for 1 h. The image shows an overlay of the fluorescent image of the beads onto the phase-contrast image to reveal the cellular outlines. Panel B: J774A.1 cells were given the indicated blocking regimens and infected with Y. pestis KIM5 for 4 h at 37°C in the presence of 40 μg/ml anti-YopM (αM) or anti-LcrV (αV) antibody. Delivery of YopH into the J774A.1 cells was determined by immunoblotting of samples of the soluble cytoplasmic fraction. Blocking treatments: FcBM, RPMI 1640 plus FcBlock plus 1% BSA pretreatment for 1.25 h at 37°C and then infection with yersiniae suspended in RPMI 1640 containing αM or αV and 1% MS; FMM, RPMI 1640 plus 10% FBS plus 1% MS pretreatment for 1.25 h at 37°C and then infection with yersiniae suspended in RPMI 1640 containing αM or αV and 1% MS; None, pretreatment with RPMI 1640 at 37°C for 1.25 h followed by infection with yersiniae suspended in RPMI 1640 containing αM or αV.