Inhibition of colony formation by macrophage committed stem cells during acute inflammation by purified human C-reactive protein (CRP).

Human C-reactive protein (CRP), an acute phase reactant purified from ascites fluids, selectively inhibited in vitro monocyte colony formation by bone marrow granulocyte-monocyte colony-forming cells (GM-CFC) from untreated mice, but not from mice that had undergone an acute systemic inflammatory response of 3-4 days duration. The CRP-susceptible M-CFC accumulated in the peritoneal cavity during the course of an inflammatory stimulus at this site. Aggregated CRP and CRP-complexes were as inhibitory as the monomeric form of purified CRP. Addition of phosphorylcholine (P-C), the major determinant on the C-polysaccharide (CPS) to which CRP binds, did not alter the inhibitory activity of CRP. Treatment of resident peritoneal macrophages with CRP did not lower their ability to serve as a source of CSF for GM-CFC. The results are consistent with a regulatory role for CRP during monocytopoiesis induced by inflammation.