O-antigen decreases the opsonization of <i>B. parapertussis</i> by <i>B. pertussis</i> vaccine-induced antibodies.

<p>Representative histograms show flow cytometric analysis of indicated bacteria opsonized with naïve serum (white) or (A) aP, (B) wP, (C) wPP-induced serum (grey) and stained with RPE-labeled goat F(ab)₂ fragments of anti-mouse IgG. (D) Mean red-fluorescence of <i>B. pertussis</i> (black), <i>B. parapertussis</i> (white), O-antigen deficient <i>B. parapertussis</i> (hatched) opsonized with indicated serum from four individual mice ± the standard error is shown. AU indicates arbitrary units. ** indicates P≤0.01.