The Vi capsular polysaccharide inhibits complement-dependent chemotaxis <i>in vitro</i>.

<p>(A and D) Neutrophil migration into the bottom compartment of a Boyden chamber containing the indicated attractants was measured in the presence or absence of the complement inhibitor Futhan. Bars represent averages ± standard error from at least 3 different donors. Vehicle; HBSS vehicle control, fMLP; <i>N</i>-formyl-L-methionyl-L-leucyl-L-phenylalanine; wt, wild type. (B) Schematic drawing of Vi capsular biosynthesis genes (black arrows) of <i>S.</i> Typhi. (C) Expression of the Vi capsular polysaccharide (Y-axis) was detected in cultures of the <i>S.</i> Typhi wild type (wt, left panel) and a non-capsulated <i>S.</i> Typhi strain (Δ<i>tviB-vexE</i> mutant, right panel) by flow cytometry using rabbit anti-Vi serum. (E) Fixation of C3b (Y-axis) on the surface of the <i>S.</i> Typhi wild type (wt, left panel) or a non-capsulated <i>S.</i> Typhi strain (Δ<i>tviB-vexE</i> mutant, right panel) that had been incubated for 30 minutes in 1% human serum was detected by flow cytometry using FITC-conjugated goat anti-human C3b antibody. (F) Quantification of C3b fixation detected by flow cytometry. A gate was set using a control in which bacteria were not stained with goat anti-human C3b antibody. Bars represent averages ± standard error from three independent experiments for each strain.