Histological and immunohistochemical characterization of joint inflammation and flare-up reactions induced by cloned MT4,Lyt-2-T cells.

This report describes the histological and immunohistochemical characterization of joint inflammations and flare-up reactions in mice induced by cloned MT4+,Lyt-2-T cells. The T-cell clone used was specific for the antigen methylated bovine serum albumin (mBSA) and was inoculated locally into a joint together with the antigen. The histological examination was performed in methylmethacrylate sections, and the various cell types were quantified in distinct regions of the knee joint. The infiltrates consisted predominantly of granulocytes admixed with small numbers of histiocytes. Few lymphocytes were present, while plasma cells were not found. Fibrosis was prominent in the later stages of the inflammation. Immunohistochemical analysis of total unfixed, non-decalcified sections using monoclonal antibodies revealed the presence of T cells which were predominantly of the helper phenotype, sporadic B cells, and a considerable number of Ia-positive cells. Macrophages were scattered throughout the infiltrate. The synovial lining was shown to express Ia antigens and to contain cells that stained with macrophage markers. Cell clusters were found including helper T (Th) cells, some B cells, and Ia-positive cells. These results are in line with immunohistological examinations in other arthritis models and resemble the early events in human rheumatoid arthritis. The data indicate that activated helper T cells are required and sufficient to give rise to the inflammatory infiltrates that are characteristic of the inflammations and exacerbations in human rheumatoid arthritis.