[Interactions between collagen and C1q: their significance for rheumatology].

Interactions between C1q and collagen are thought to be due to the similarity in the structure of collagen and part of C1q. In the present paper immunological and biochemical aspects of this similarity were explored. It was found that one of nine rabbit anticollagen sera studied showed a clearcut reactivity with C1q, while anticollagenantibody-positive sera and synovial fluids of patients with rheumatoid arthritis did not display any cross-reactivity with C1q. Eleven of twenty collagen-immunized guinea pigs, however, demonstrated cellular cross-reactivity with CLF, the collagen-like fragment of C1q. Gel filtration studies indicated the formation of complexes between CLF and collagen, simulating immunological inhibition of anti-C1q-antibody by collagen. Human RA synovial collagenase was found capable of splitting C1q at a position within its collagen-like fragment. The importance of the interactions between collagen and C1q for the pathological events characterizing RA is discussed.