Objective: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the formation of antinuclear autoantibodies. Increased apoptosis and reduced clearance of apoptotic material have been assigned a role in the pathogenesis of SLE, but the underlying mechanisms remain elusive. During apoptosis apoptotic blebs are formed in which autoantigens are clustered. The cellular remnants after blebbing are referred to as apoptotic cell bodies. We undertook this study to compare the effects of apoptotic blebs and apoptotic cell bodies on maturation of dendritic cells (DCs) and their T cell stimulatory capacity in a murine setting.
Methods: The uptake by DCs of apoptotic blebs and apoptotic cell bodies was analyzed by flow cytometry and confocal microscopy. DC maturation and DC-induced T cell activation were determined by measuring expression of costimulatory molecules using flow cytometry and by measuring production of cytokines using enzyme-linked immunosorbent assay.
Results: DCs internalized apoptotic blebs more efficiently than apoptotic cell bodies. Incubation of DCs with apoptotic blebs resulted in increased CD40 and CD86 expression and increased interleukin-6 (IL-6) and tumor necrosis factor alpha production, while apoptotic cell bodies had no stimulatory effects. Using chloroquine, apoptotic bleb-induced DC maturation was shown to be independent of Toll-like receptors 3, 7, and 9. Interestingly, in cocultures with allogeneic T cells, bleb-matured DCs induced production of IL-2, interferon-gamma, and, in particular, IL-17, suggesting a Th1/Th17 response.
Conclusion: Apoptotic blebs, in contrast to apoptotic cell bodies, induce DC maturation, thereby providing DCs with increased Th17 cell stimulatory capacity. These data imply that apoptotic bleb-induced DC maturation represents an important driving force in the autoimmune response in SLE.