Increased expression of C1q receptors on neutrophils from inflammatory joint fluids.

C1q receptor (C1qR) expression was determined by immunofluorescence flow cytometry on neutrophils from paired peripheral blood and synovial fluid samples from 21 patients with rheumatoid arthritis (RA) and 13 patients with other articular diseases (OAD). In both patient groups the levels of C1qR on circulating neutrophils were similar to that observed for normal control subjects, whereas on synovial fluid neutrophils significantly higher levels of receptor expression were observed. The mean percentage increases observed were: RA patients 47%, OAD patients 72%. C1q-bearing immune complexes were most prevalent in patients with RA, with the highest concentrations being found in synovial fluid samples. No correlation between immune complex levels and neutrophil C1qR expression was noted. Upregulation of C1qR expression is a feature of activated neutrophils from inflammatory joint fluids.