The biological and biochemical effect of modified forms of C-reactive protein on human neutrophils

Previous work from this laboratory demonstrated that C-reactive protein (CRP) is elevated in patients with the inflammatory disease, Acute Respiratory Distress Syndrome (ARDS) and that there is a trend of increased CRP serum levels that coincides with survival of ARDS patients. Native, pentameric CRP was shown to be associated with neutrophils at local sites of inflammation in addition to an antigenically distinct, modified form of CRP. Modified CRP was shown to potentiate neutrophil respiratory burst and to activate platelets, but its effect on human neutrophil chemotaxis remains unclear. Acid modified CRP (aCRP) and recombinant modified CRP (rmCRP) were characterized and shown to be aggregates of CRP monomers, antigenically distinct from native CRP. To assay the effect of modified CRP on neutrophil chemotaxis, neutrophils were pretreated with aCRP and rmCRP. aCRP and rmCRP inhibit fMLP and IL-8-stimulated neutrophil chemotaxis in a concentration-dependent manner in vitro . aCRP significantly inhibited neutrophil cell movement in a fMLP-induced acute lung injury model in mice, while rmCRP did not have a significant effect at any of the concentration tested. Protection of lung injury as measured by increased total protein leak was not observed with any of the forms of CRP. Heterologous binding experiments indicated that both human and rabbit native CRP bind to the same receptor. Native and modified forms of CRP interact through the C-terminal sequence CRP199-206, causing an increase of labeled, native CRP binding to neutrophils interfering with heterologous binding experiments to determine whether modified CRP binds the native CRP receptor. aCRP binds to CD 16 on human neutrophils, while no significant binding was seen with native CRP or rmCRP. In conclusion, aCRP inhibits fMLP-induced neutrophil cell movement in vitro and in vivo possibly by a mechanism involving the low affinity IgG receptor. rmCRP inhibits neutrophil cell movement in vitro but not in vivo .