Are levels of soluble C1q binding proteins in plasma/serum and synovial fluid indicative or prognostic in the course of Rheumatoid Arthritis and SLE? : development of pathway specific assays, to monitor activity of complement activation complexes in human and murine serum/plasma samples

The aims of my PhD project were a) to determine the levels of C1q-binding proteins (gC1qBP and calreticulin) in (i) normal serum, (ii) serum/plasma samples of patients diagnosed with rheumatoid arthritis and systemic lupus erythematosus and (iii) synovial fluid samples of patients diagnosed with rheumatoid arthritis. For this, coding cDNA sequences for gC1qBP and calreticulin were cloned and expressed recombinant proteins were purified and used to develop functional ELISA assays. It was observed that calreticulin levels were significantly increased in the synovial fluid samples of patients diagnosed with rheumatoid arthritis as compared to synovial fluid samples of patients diagnosed with osteoarthritis. gC1qBP was found to be significantly increased in the serum samples of patients diagnosed with systemic lupus erythematosus and decreased in synovial fluid samples of patients diagnosed with rheumatoid arthritis, as compared to serum samples of healthy control individuals. b) to establish functional assays to measure complement activation in human, murine and guinea pig sera. I investigated for potential MBL ligands and demonstrated MBL binding and lectin pathway activation using the pneumococcal vaccine Pneumovax II and Acanthamoeba (whole cells) trophozoites and cysts. CR1 has been described as a ligand for MBL. I tested this hypothesis using functional ELISA assays. In contrast to conclusions in a previous report of another research group, my results show that soluble CR1 binds to C1q but not to MBL. The results presented in my thesis also provide strong evidence that CR1 appears not to interact directly with MBL or MBL-mediated lectin pathway activation as the addition of soluble CR1 to my lectin pathway activation assay has no effect whatsoever on C4 cleavage. Nevertheless, sCRl regulates lectin pathway activation further downstream and significantly inhibits lectin pathway mediated C3 cleavage, most likely by the decay accelerating and co-factor activity of sCRl in the factor I-mediated inactivation of either C4b or C3b. Using the C3 cleavage assay and murine strains deficient in C1q, factor B and factor B/C2, I showed the importance of the amplification loop of the alternative pathway in complement activation. Finally, using the C3 cleavage assay with guinea pig serum deficient in complement component C4, it was demonstrated that MASP-1 does not appear to be an effective enzyme in cleaving C3, as proposed by others.