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Regulation of the function of the first component of complement by human C1q receptor
Author(s) -
van den Berg Rocco H.,
FaberKrol Maria,
van Es Leendert A.,
Daha Mohamed R.
Publication year - 1995
Publication title -
european journal of immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 201
eISSN - 1521-4141
pISSN - 0014-2980
DOI - 10.1002/eji.1830250814
Subject(s) - complement system , complement c1q , biology , cd46 , complement membrane attack complex , microbiology and biotechnology , complement receptor 1 , cd59 , complement component 2 , receptor , complement control protein , complement receptor , anaphylatoxin , classical complement pathway , alternative complement pathway , complement (music) , function (biology) , c5a receptor , lysis , biochemistry , immune system , phenotype , immunology , gene , complementation
Abstract A membrane‐associated receptor for the C1q subcomponent of complement is widely distributed among different cell types. While a number of possible physiological functions of the C1q receptor (C1qR) on different cell types have been described, the way in which C1qR regulates complement activity remains unclear. This report describes the mechanism by which C1qR regulates activation of the first component of complement, C1. Using purified components of complement, we were able to show that membrane‐associated C1qR as well as detergent‐solubilized C1qR, purified from polymorphonuclear leukocytes, human umbilical vein endothelial cells or an endothelial cell line, EA.hy 926, are able to inhibit complement‐mediated lysis of C1q‐sensitized erythrocytes. Using hemolytic assays, we were able to demonstrate that C1qR prevents the association of C1q with C1r and C1s to form macromolecular C1. In addition, incubation of C1qR with the collagen‐like stalks, but not with the globular heads of C1q, inhibits the effect of C1qR. This demonstrates that C1qR exerts its complement inhibitory effect by binding to the collagen‐like stalk of C1q. No complement regulatory effect of C1qR was observed on preformed macromolecular C1. These data suggest that besides such well‐known complement regulatory molecules as CD55 (DAF), CD46 (MCP), CD35 (CR1) and CD59 (HRF), C1qR too is able to regulate complement activity.