Figure 4.

(A) The addition of purified SipA-HA permits S. typhimurium strain EE633 to induce PMN transepithelial migration. The purified recombinant SipA-HA fusion protein was added to 1.25 × 10⁸ sipA mutant S. typhimurium (EE633) at a final concentration of (0.2–20 μg/ml) just before and during a 1-h bacterial infection at the apical surface of T84 cell monolayers. Elicitation of PMN transepithelial migration subsequently was measured. Data represent the mean ± SD of triplicate samples; (*, not significantly different from levels induced by WT). (B) Purified SipA-HA is sufficient to induce PMN transepithelial migration. The apical surface of T84 cell monolayers was exposed to varying amounts of SipA-HA (empty bars). After 1 h at 37°C, excess SipA-HA was removed, PMN were added to the basolateral membrane interface, and PMN migration was assessed. Alternatively, 60 μg/ml of α-SipA mAb was added to purified SipA (20 μg/ml) 30 min before and during the 1 h incubation with the T84 cells (filled bar). PMN transmigration is compared with that induced by WT S. typhimurium (gray bar). Data represent the mean ± SD of triplicate samples.