Altered apoptosis can lead to autoimmune diseases such as systemic lupus erythematosus (SLE). Juvenile idiopathic arthritis (JIA) is another autoimmune disease characterized by autoinflammation. During this process activated T-cells accumulate in the synovial fluid. We hypothesized that resistance to CD95-mediated apoptosis could contribute to autoimmune phenotypes.
We isolated highly activated T cells (CD45RO+ and CD95+) by magnetic separation from healthy controls, JIA patients and patients with other autoimmune diseases. In these purified cells, apoptosis was induced by stimulation with recombinant human soluble CD95 ligand (rhsCD95L) or dexamethasone and analyzed by flow cytometry. In addition, cleavage and expression of apoptosis mediators (Caspase-8 and -3) and regulators (FLIP, Bcl-2, Bcl-xL) were analyzed in mononuclear cells using immunoblot technique.
Apoptosis upon CD95 stimulation, but not dexamethasone treatment, was reduced in JIA patients and patients with other autoimmune diseases compared to healthy controls. Additionally we observed a non-canonical cleavage pattern of Caspase-8 resulting in a p22 fragment and high expression of FLIP in SFMCs of patients with JIA.
Expression and cleavage of proteins of the CD95 pathway is altered in JIA providing a possible explanation for resistance against death receptor-mediated apoptosis. Dexamethasone-induced apoptosis, however, is intact arguing against a general defect in apoptosis. The implications of the p22 fragment regarding apoptosis have to be further analyzed. The strong expression of FLIPShort in SFMCs may as well result from the highly activated status of the cells or be a feature of autoimmunity.