Analysis of receptor-mediated C1q binding to human peripheral blood mononuclear cells.
The binding of C1q to human peripheral blood leukocytes has been investigated. Studies with fluorescein conjugated F(ab')2 anti-C1q show that few (0 to 4%) normal leukocytes isolated in the presence of EDTA have C1q on their surface. However, approximately 26% of the mononuclear cell population is able to bind added C1q. Quantitative binding studies using 125I-C1q show that the binding to mononuclear cells is specific, saturable, and reversible. Scatchard plot analyses indicate an approximate equilibrium constant of 1.2 times 10(7) M-1. C1q binding appears to be mediated via the collagenous portion of the molecule in that 1) type I collagen inhibits this binding; 2) C1 reconstituted from purified C1q, C1r, and C1s does not bind to mononuclear cells, whereas the same amount of free C1q binds avidly; and 3) C1q enhances the binding of aggregated IgG to mononuclear cells.
D001665:Binding Sites; D003094:Collagen / Q000494:pharmacology; D003172:Complement C1; D003179:Complement C3b; D004306:Dose-Response Relationship, Immunologic; D005353:Fibronectins / Q000494:pharmacology; D006801:Humans; D010586:Phagocytes / Q000276:immunology*; D011951:Receptors, Complement; D011961:Receptors, Fc
D003172:Complement C1; D005353:Fibronectins; D011951:Receptors, Complement; D011961:Receptors, Fc; D003179:Complement C3b; D003094:Collagen