Reactivity to collagen type II and C1q in rheumatic diseases

In rheumatoid arthritis (RA),other arthritides and in systemic lupus erythematosus (SLE) there is immunological reactivity to collagen type II (CII) and to complement component C1q. Parts of the CII and C1q molecules are structurally and immunologically related. Both cellular and humoral responses to CII may be implicated in the pathogenesis of human arthritis. Humoral anti-C1q reactivity associates with the development of proliferative forms of SLE nephritis.

The aim of this thesis was to investigate reactivity to CII and C1q in RA and SLE. In many instances, ELISPOT techniques which enumerate the numbers of cells producing antibodies or cytokines, were used. Cells spontaneously producing antibodies to CII were found in synovial fluid mononuclear cells (SFMC) of half of the RA patients investigated. Serological tissue typing demonstrated that only patients possessing any of the RA-associated HLA-DR phenotypes showed spontaneous anti-CII production in SF, and a significant association to the occurrence of HLA-DR4 was detected. When mononuclear cells from SF of arthritis patients were cultured together with native CII, significantly higher amounts of Tumour Necrosis Factor-a (TNF-a) were produced compared to when cells were cultured with heat-denatured CII.

Cell depletion experiments showed CD 14+ cells to be responsible for this TNF-a production. When the commonly used nitrocellulose plates were exchanged for plastic plates in the ELISPOT for the measurement of single cells producing interferon-y (IFN-y), the plastic plates showed advantages concerning both sensitivity and specificity. When the plastic-plate method was applied to SFMC and peripheral blood mononuclear cells (PBMC) of arthritis patients, spontaneous production of both IFN-y and of interleukin (IL)-4 were significantly increased in SF. Spontaneous IgG anti-C1q production was found in PBMC of SLE patients with active disease, and was found to decrease following steroid therapy in serially followed patients. When this finding of high numbers of anti-C1q producing cells at peak clinical activity was used in a cross-sectional study of SLE patients with active disease, high numbers of IgG anti-C1q producing cells were only found in PBMC of patients with biopsy-proven proliferative forms of SLE nephritis.

In a comparative study, levels of autoantibodies were assessed in serial and cross-sectional investigations of SLE and RA patients. Serum levels of anti-C1q were found not to vary in parallel to anti-CII in RA or SLE patients, whereas a positive correlation was found between anti-C1q and antibodies directed against complement factor C3 in SLE patients. A hypothesis concerning the development of anti-C1q antibodies is presented. Local anti-CII production in RA synovial fluid implicates its importance in local immune complex formation. The association between HLA-DR4 and IgG anti-CII production suggests a pathogenetic role for T cells in the RA disease process. Local production of inflammatory monokines close to the eroding cartilage may be partly explained by TNF-ac production by monocytes/macrophages stimulated with native CII. The significantly increased number of cells producing T cell cytokines in SFMC argue for functionally activated T cells within the inflamed joint. The anti-C1q ELISPOT might be a useful tool for screening of nephritis in SLE patients.