Background: Although autoimmunity in MRL/lpr mice occurs due to a defect in Fas-mediated cell death of T cells, the role of Fas-independent apoptosis in pathogenesis has rarely been investigated. We have recently reported that receptor activator of nuclear factor (NF)-kappa B ligand (RANKL)-activated dendritic cells (DCs) play a key role in the pathogenesis of rheumatoid arthritis (RA) in MRL/lpr mice. We here attempted to establish a new therapeutic strategy with RANKL-activated DCs in RA by controlling apoptosis of peripheral T cells. Repeated transfer of RANKL-activated DCs into MRL/lpr mice was tested to determine whether this had a therapeutic effect on autoimmunity.
Methods and Finding: Cellular and molecular mechanisms of Fas-independent apoptosis of T cells induced by the DCs were investigated by in vitro and in vivo analyses. We demonstrated that repeated transfers of RANKL-activated DCs into MRL/lpr mice resulted in therapeutic effects on RA lesions and lymphoproliferation due to declines of CD4(+) T, B, and CD4(-)CD8(-) double negative (DN) T cells. We also found that the Fas-independent T-cell apoptosis was induced by a direct interaction between tumor necrosis factor (TNF)-related apoptosis-inducing ligand-receptor 2 (TRAIL-R2) on T cells and TRAIL on Fas-deficient DCs in MRL/lpr mice.
Conclusion: These results strongly suggest that a novel Fas-independent apoptosis pathway in T cells maintains peripheral tolerance and thus controls autoimmunity in MRL/lpr mice.