CRP enhances phagocyte responses of PMN toward IgG-opsonized platelets. (A) B2G1-specific respiratory burst activity of 14 NHS correlates significantly with the CRP concentrations in the sera. (B) Both CRP and calcium were required to induce IgG-specific respiratory burst. B2G1-opsonized platelets were incubated in HEPES supplemented with or without calcium and in the presence or absence of CRP, before addition of PMN to measure the respratory burst. (C) Depletion from NHS with phosphocholine-coated beads neutralized its ability to enhance IgG1-mediated respiratory burst toward B2G1-opsonized platelets, but resupplementing CRP restored this capacity. (D) CRP addition to NHS with low CRP (0.07 mg/L) rendered the serum capable of inducing IgG-specific respiratory burst toward B2G1-opsonized platelets that correlated significantly with the amount of CRP added. Data are representative of 3 independent experiments, showing mean ± standard deviation. Statistical comparisons were performed as follows: (A,D) Pearson correlation; (B-C) 2-way ANOVA with Bonferroni posttest. *P ≤ .05; **P ≤ .01; ***P ≤ .001.