SIMILARITIES AND DISSIMILARITIES BETWEEN THE BINDING ABILITY OF CLQ AND COLLAGEN

  • 1 January 1981
    • journal article
    • research article
    • Vol. 44  (1) , 181-190
Abstract
Based on chemical-structural similarities between C1q [complement component 1q] and collagen [CG], their activities were studied in reactions which are typically induced by CG or mediated by C1q. Human C1q suppressed the CG-induced platelet aggregation in human platelet-rich plasmas. Both human C1q and a suspension of insoluble bovine CG inhibited in a time-dependent fashion the lysis of sensitized sheep erythrocytes (EA [antibody-coated erythrocytes]) by guinea pig complement. They both agglutinated sheep erythrocytes (EA and EAC4 [erythrocyte-antibody-C4 complex]) sensitized with rabbit hemolysin, mainly of the IgM type, polystyrene latex particles complexed with heat-denatured human IgG, a combination of horse, goat and sheep globulins, or deoxyribonucleoprotein. Heating of C1q and CG (56.degree. C, 30 min), which disrupts the CG fold into a random coil structure, almost completely abrogated all activities of C1q and considerably reduced those of CG, suggesting that an intact triple helix is essential for their activities. Despite their far-ranging similarities, C1q was more potent by weight in most reactions, showed evidence of a faster rate of EA binding and was more sensitive to heat treatment at 56.degree. C than was collagen. A model is proposed according to which platelets, sensitized erythrocytes, aggregated .gamma.-globulins, immune complexes and deoxyribonucleoprotein might accumulate at the endothelial damage site where blood and its components are exposed to collagenous substances. C1q is able to inhibit all these reactions; C1q is collagen-like in its behavior and collagen also has C1q-like properties.