To assess the expression of tumor necrosis factor alpha (TNF alpha), TNF beta, and their receptors in synovia of patients with juvenile rheumatoid arthritis (JRA) and juvenile spondylarthropathy (JSpA), and to determine similarities with and differences from adult RA.
Twenty-eight synovial tissue samples from patients with JRA, 6 from patients with JSpA, and 6 from patients with RA, selected for the presence of inflammatory infiltrates, were analyzed for the expression of TNF alpha, TNF beta, and their receptors (p55 and p75 TNFR), utilizing the dual approach of reverse transcriptase-polymerase chain reaction and immunohistochemistry analysis.
The presence of both TNF alpha and TNF beta expression was demonstrated in most JRA and JSpA tissues, although samples from patients with pauciarticular JRA had somewhat lesser amounts of these cytokines. TNF beta expression correlated significantly with the occurrence of lymphocytic aggregates in tissues. Staining with monoclonal antibodies specific for the p55 and p75 receptors revealed that a diverse range of cell types expressed the receptors, with the most intense p55 staining on vascular endothelial cells. In the vast majority of synovial tissues, far greater numbers of cells expressed the p55 form of the receptor than the p75 form.
JRA and JSpA synovia are characterized by the presence of TNF alpha, TNF beta, and cells expressing TNFR. These findings provide further evidence that TNF, through autocrine/paracrine mechanisms, may amplify local inflammation, leading to joint destruction. The prominence of TNF beta in the synovium in particular subgroups of JRA patients and in JSpA patients may be a distinguishing feature of these diseases.