Critical role of Kupffer cell CR3 (CD11b/CD18) in the clearance of IgM-opsonized erythrocytes or soluble β-glucan

Liver macrophages (Kupffer cells) play a major role in blood clearance of both C3-opsonized immune complexes and therapeutic beta-glucan polysaccharides, Human Kupffer cells express three types of C3-receptors: CR1 (C3b-receptor; CD35), CR3 (iC3b- and beta-glucan-receptor), and CR4 (iC3b-receptor; CD11c/CD18). Studies of isolated macrophages have suggested that CR3 is the major receptor mediating capture of either C3-opsonized erythrocytes (E) or beta-glucans. In this investigation, the organ distribution and function of CR3 in the clearance of IgM-opsonized E and soluble CR3-binding polysaccharides were explored in normal vs. CR3-knockout (CR3-KO) mice. Analysis of intravenously (i.v.) injected I-125-anti-CR3 showed that the major vascular reservoir of CR3 was the liver, followed by spleen and lungs. By contrast, clearance of I-125-anti-CR1 appeared to be mediated predominantly by splenic B lymphocytes, as only subsets of splenic macrophages or Kupffer cells were found to express CR1. Clearance of lgM-opsonized Cr-51-E occurred rapidly to the livers of normal mice but was nearly absent in CR3-KO mice. Soluble I-125-beta-glucan exhibited rapid clearance to the liver in normal mice, whereas clearance in CR3-KO mice was significantly reduced. In conclusion, Kupffer cell CR3 plays a crucial role in the clearance of both IgM-opsonized E and beta-glucans. (C) 2000 Published by Elsevier Science B.V. All rights resented.