Berhane Ghebrehiwet and 2Ellinor I B Peerschke

1State University of New York, Stony Brook, New York 2Weill Medical College of Cornell University, New York, New York

The first component of complement, C1, is a multimole-cular complex comprising C1q and the Ca2+-dependent tetramer C1r2-C1s2. The primary role of C1q within the complex is that of a recognition signal, which triggers activation of the classical pathway of complement. However, C1q is also able to bind to a variety of cell types in a manner that induces specific biological responses. Interaction of C1q with endothelial cells, for example, leads to cellular activation followed by release of biological mediators and/or expression of adhesion molecules, all of which contribute, directly or indirectly, to the inflammatory process. These specific responses are thought to be mediated by the interaction of C1q with proteins of the endothelial cell surface. Endothelial cells express four types of putative C1q binding proteins/receptors: cC1q-R/CR, or calreticulin (CR), a 60-kDa collectin receptor; gC1q-R/p33, a 33kDa homotrimeric protein; C1q-Rp (CD93), a 129-kDa O-sialoglycoprotein; and CR1 (CD35), the receptor for C3b. Although the specific role of each of these molecules in the C1q-mediated biological responses is yet to be worked out, all of them may, in one fashion or another, participate in the inflammatory processes and vascular lesions that occur on the endothelium.

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Essentials of Human Physiology

Essentials of Human Physiology

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