Functional studies of T-cells in rheumatoid arthritis

Abstract: Rheumatoid arthritis (RA) is a systemic inflammatory disease with autoimmune features primarily affecting the joints. The etiology of RA is largely unknown but involvement of the immune system in the disease process is evident from the infiltration of leukocytes into the joint, and by the production of proinflammatory cytokines, chemokines and proteases, mainly by macrophages. T- cells are believed to be of importance due to the association of HLA class II with RA and the fact that phenotypically activated T-cells are abundant in the inflamed joint. Whether the disease is driven by autoreactive T-cells or T-cells activated by some other means are topics addressed in the present study. We detected an increased frequency of cells producing T-cell derived cytokines ex vivo in synovial fluid (SF) compared to peripheral blood (PB) in patients with inflammatory joint disease. These results prompted us to make a detailed characterisation of in vitro reactivity of T-cells in SF and PB from RA patients. We found that RA synovial fluid mononuclear cells (SFMC) proliferate poorly and produce less cytokines compared to RA PBMC when stimulated through the T-cell receptor (TCR) with anti-CD3 antibodies. A low expression of the TCR associated signalling chain CD3[delta] in SF T-cells, but not in PB T-cells, may partly explain this TCR-dependent hyporesponsiveness. We demonstrated that granulocytes, which are abundant in the inflamed joint fluid, have the ability to downregulate T-cell effector functions as well as CD3[delta] expression in vitro. By stimulation with phorbol 12-myristate 13-acetate (PMA), thereby bypassing signalling through the TCR, SF T-cells produced more IFN-[gamma] than did PB T-cells. This hyperresponsiveness may be explained by MHC-independent mechanisms (e.g. IL-12 production) upregulated in SF-derived accessory cells. We investigated T-cell reactivity to the major cartilage-derived antigen, collagen type II (CII), in RA patients and healthy controls (HQ and determined an increased CII-specific T-cell reactivity in RA patients. This increased cellular reactivity to CH was specifically detected in RA patients carrying the disease associated genes HLA-DRB1'0401 or HLA-DQA'0301-DQB'0302 (HLA- DQ8), but was not evident in HC with these genotypes. We observed that in vitro peripheral T-cell responses to CII as well as to other antigens increased after treatment of RA patients with TNF- [alpha] blockade therapy. These results indicate that TNF-[alpha] may act as a T-cell suppressor in RA patients. Two RA patients with previously determined clinical response to oral CH treatment were monitored immunologically during and between periods of oral CH treatment. An increased T-cell function, measured as ex vivo produced IFN-[gamma] as well as CII-specific IFN-[gamma], was evident during some off-treatment periods.