To show the involvement of lymphocyte-derived catecholamines in the pathogenesis of rheumatoid arthritis (RA), we investigated the change in expression of tyrosine hydroxylase (TH), a rate-limiting enzyme of catecholamine synthesis, by CD4+ T lymphocytes in lymphoid tissues of DBA/1 mice with collagen-induced arthritis (CIA).
CIA model was induced by chicken type II collagen in DBA/1 mice. The joints of the mice were observed for clinical score of swelling on and after the 22nd day of primary immunization. Pathological changes of ankles were examined by staining of tissue sections with hematoxylin and eosin on the 35th and 55th day following primary immunization. Immunofluorescent histochemistry was used to identify the number of TH-positive, CD4-positive, and double-labeled cells in the mesenteric lymph nodes and the spleen.
Paw-swelling onset was on days 29 - 32 after the first immunization in DBA/1 mice. Clinical score for swelling of the paws reached peak on day 46 after the first immunization. Compared with the ankles of intact or vehicle mice, the joints of CIA mice had these characteristics: increased inflammatory cells in the synovial tissues, proliferated synoviocytes in the multilayers, narrowed articular space, and destructed articular cartilages. Simultaneously, the number of TH-positive, CD4-positive, and double-labeled cells in the mesenteric lymph nodes and the spleen was significantly increased on days 35 and 55 following the first immunization. Between day 35 and day 55 post-immunization, there was no significant difference in the number of these positive cells.
CD4+ T lymphocytes up-regulate TH expression in the process of CIA and therefore, it is suggested that endogenous catecholamines of lymphocytes involve in the pathogenesis of RA.