FIGURE 1.

Additive binding of C4BP and plasminogen to S. pneumoniae. A and B, schematic representation of the different variants of C4BP used: C4BP-PS (A) and rC4BP (B). The main isoform of C4BP contains seven identical α-chains and one unique β-chain. The β-chain-containing C4BP in circulation is bound to vitamin K-dependent anticoagulant Protein S (PS), forming a C4BP-PS complex. The rC4BP contains six α-chains and lacks the β-chain and the associated PS. C and D, increased binding of C4BP to pneumococci in the presence of plasminogen. Binding of C4BP-PS (C) and rC4BP (D) to pneumococci was analyzed in the presence or absence of plasminogen, by flow cytometry. The geometric mean fluorescence intensity (GMFI) and S.D. calculated from three independent experiments are shown. Bac only represents bacteria that were neither incubated with protein nor Abs, whereas the Ab background represents bacteria incubated with Abs only. A one-way analysis of variance test was used to calculate statistical significance. ns, not significant; **, p < 0.01; ***, p < 0.001.