INFLAMMATORY INFILTRATE AND INTERLEUKIN-8 EXPRESSION IN THE SYNOVIUM OF PSORIATIC-ARTHRITIS - AN IMMUNOHISTOCHEMICAL AND MESSENGER-RNA ANALYSIS

Psoriatic arthritis is an inflammatory arthropathy that ultimately can lead to joint destruction. In this study, we investigated the immunop henotype of the inflammatory cells and the expression of interleukin-8 (IL-8), which is the hallmark chemoattractant cytokine of psoriasis i n synovial membranes from patients exhibiting active psoriatic synovit is (n=9). The tissue samples were examined by immunohistochemistry, We stern blot analysis and in situ hybridisation. The inflammatory infilt rate consisted predominantly of CD3(+) T lymphocytes, with a higher pr oportion of CD4(+) than CD8(+) T lymphocytes in six cases. CD3(+) T ly mphocytes were focally distributed near small blood vessels and the en larged synovial intima. CD1(+) interdigitating reticulum cells were no t detected. CD22(+) B lymphocytes and plasma cells were found in small aggregates without KiM4(+) follicular dendritic cells. KiM8(+) macrop hages were located in the synovial intima and were distributed in a di ffuse pattern near the synovial lining cells. CD15(+) neutrophil granu locytes were detected in four cases. They were preferentially located in the vicinity of blood vessels and the synovial intima. IL-8 was fou nd at a high level in the synovial lining cells and to a lesser extent in cells located in the perivascular areas. Immunofluorescence double staining showed IL-8 to be expressed in KiM8(+) multinucleated giant cells, KiM8(+) macrophages and CD3(+) T lymphocytes. IL-8 receptor A w as demonstrated in the synovial lining and in macrophages and lymphocy tes. IL-8 was detected by immunoblot analysis of the synovial tissue a t 8.4 kD. Employing in situ hybridisation, IL-8 mRNA was strongly and preferentially expressed in the synovial intima, as well as in macroph ages and lymphocytes. The immunophenotype of the psoriatic arthritis i nflammatory cells shows great similarity to the inflammatory infiltrat e found in the synovial tissue of patients with rheumatoid arthritis. The preferential expression of IL-8 and IL-8 mRNA in the enlarged syno vial intima and in lymphocytes and macrophages suggests that IL-8 exer ts its action through activated mononuclear cells and T lymphocytes. I t seems to play a role in regulating leucocyte traffic into the enlarg ed synovial intima and may contribute to the aggressive synovitis of p atients with psoriatic arthritis.