Specific binding of the human anti-F1 IgG1 to the <i>Y. pestis</i> cell surface was detected by a flow cytometry assay.

<p>A mouse anti-<i>B mallei</i> IgG1was used (10 µg/ml) as an isotype mAb control, and the mouse anti-F1 (F1-04-A-G1, F1m) mAbs was used (10 µg/ml) as a positive IgG1 control. <i>Y</i>. <i>pestis</i> grown at 26°C (top panel) was used as an anti-F1 mAb negative control. <i>E.coli</i> grown at 37°C was used as a specificity control for anti-F1 and anti-V IgGs.