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Rheumatoid arthritis (RA) synovial fluid (SF) T cells express the activation markers CD69, HLA-DR and very late antigen (VLA)-1, but surprisingly few bear interleukin-2 receptors (CD25). This unusual activation state is commonly assumed to be due to stimulation by local antigen, yet T cells activated in vitro express activation antigens in the clearly defined sequence: CD69, CD25, HLA-DR and finally VLA-1. Two possible explanations for the activation state of SF cells are: first, they comprise several subpopulations each expressing different activation antigens or, second, activation markers are up-regulated by mechanisms other than antigen stimulation. To examine these hypotheses, double- and triple-color immunofluorescence techniques were applied to four T cell populations: normal peripheral blood T cells activated in vitro, RA SF T cells, T cells from an in vivo model of migration [tuberculin purified protein derivative (PPD)-induced skin blisters] and T cells co-cultured with endothelial cells (EC). The results confirmed that in vitro activated T cells expressed activation markers in the sequence described above, with significant CD25 expression and few cells co-expressing CD69 with HLA-DR or VLA-1. In contrast, almost half the SF T cells were CD69+HLA-DR+ but CD25-; a significant minority were CD69+VLA-1+. T cells from PPD-induced skin blisters were already HLA-DR+ and VLA-1+ at 24 h, although, in vitro, PPD-activated T cells up-regulated HLA-DR and VLA-1 only after 1 week, suggesting that pre-activated T cells were preferentially recruited into the blisters. Finally, T cells were found to up-regulate CD69 and, to a lesser extent, HLA-DR after adhering to EC in vitro. In summary, the paradoxical activation state of SF T cells cannot be explained solely by single or multiple rounds of activation in situ. At least two other mechanisms, the preferential recruitment of pre-activated T cells and the induction of HLA-DR and especially CD69 by endothelial contact during migration, may also play a role.

The occurrence of certain antibacterial antibodies was studied in the sera of 22 healthy donors (HD) and 66 patients with different diseases. The cases investigated included 22 rheumatoid arthritis (RA), 22 non-arthritic-psoriasis (NAP), and 22 psoriatic arthritis (PA) patients. A complement fixation test was used with Yersinia enterocolitica 0:3 type (YEC), Yersinia pseudotuberculosis (YPT), Campylobacter jejuni (CJ), and Campylobacter fetus (CF) antigens; the detection of anti-Chlamydia trachomatis (CT) antibodies was carried out using an immunoperoxidase colorimetric slide test that allowed the detection of isotypes of specific antibodies. It was found that the synthesis of anti-CF, CJ, YEC, and YPT antibodies in NAP patients does not differ significantly from that of the HD group; on the contrary, the antibody levels were statistically higher in PA than in the other disease groups or in the healthy controls, although only anti-CF antibodies seemed to significantly differentiate (p = 0.000003) the PA group from the others. Anti-CT IgA antibody titers were found to be significantly higher in the PA as well as in the RA groups when compared with the controls, while the antibody levels in NAP patients showed no clear-cut difference with respect to those of either the arthritic patients or the healthy controls. By showing that anti-enterobacterial antibodies are increased in PA but not in NAP patients, our data furnish additional support to the thesis of a pathogenic role of bacterial infections in psoriatic arthritis.

Decreased levels of angiotensin converting enzyme plasma activity were found in systemic sclerosis. No relationship with clinical characteristics of the disease and increased von Willebrand factor antigen concentration (a widely accepted marker of endothelial injury) were statistically demonstrated. An inverse relationship between the reduced activity of the enzyme and erythrocyte sedimentation rate was detected (r = 0.410, p less than 0.05). We hypothesize that in systemic sclerosis, angiotensin converting enzyme activity might be affected by a decrease in endothelial production or by interference of circulating factors. Further studies are needed to determine if angiotensin converting enzyme activity could be used as a marker of endothelial injury in scleroderma.