Characterization of the human C1q receptor.

At the meeting new procedures were reported for the isolation of the receptor which binds to the collagen-stalks of C1q, a subcomponent to the macromolecular complex, C1. The C1q-receptor was isolated from human tonsil cells, by a two-step procedure which did not involve affinity chromatography on C1q-Sepharose. In solution the C1q-receptor from tonsil cells behaved as an elongated dimer of two approx. 60 kDa chains. A C1q-receptor preparation isolated from human phagocytes, using pepsin-digested C1q for affinity chromatography, was found to be predominantly a molecule of approx. 120 kDa as assessed by SDS-PAGE. The amino acid compositions of C1q-receptor preparations derived from Raji (B-lymphoblastoid) and U937 (monocytic) cell-lines were found to be very similar. These results suggest that the human C1q-receptor may be a one-chain molecule, and also raise the possibility that there is more than one type of C1q receptor on cell surfaces.