Objective. In systemic lupus erythematosus (SLE), inadequate removal of apoptotic cells may lead to challenge of the immune system with immunogenic self antigens that have been modified during apoptosis. We undertook this study to evaluate whether apoptosisinduced histone modifications are targets for the immune system in SLE.Methods. The epitope of KM-2, a monoclonal antihistone autoantibody derived from a lupus mouse, was mapped by random peptide phage display. The reactivity of KM-2 and plasma with (acetylated) histone H4 (H4) peptides and with nonapoptotic, apoptotic, and hyperacetylated histones was determined by immunofluorescence staining, enzyme-linked immunosorbent assay, and Western blotting.Results. KM-2 recognized apoptosis-induced acetylation of H4 at lysines 8, 12, and 16. The majority of plasma samples from SLE patients and lupus mice showed higher reactivity with triacetylated H4 peptide (residues 1-22) and with hyperacetylated and apoptotic histones than with nonacetylated H4 peptide and normal histones. Importantly, administration of triacetylated H4 peptide to lupus-prone mice before disease onset accelerated the disease by enhancing mortality and aggravating proteinuria, skin lesions, and glomerular IgG deposition, while the nonacetylated H4 peptide had no pathogenic effect. The delayed-type hypersensitivity response in lupus mice against the triacetylated H4 peptide was higher than that against the nonacetylated H4 peptide. Bone marrow-derived dendritic cells (DCs) cultured in the presence of hyperacetylated nucleosomes showed increased expression/production of CD40, CD86, interleukin-6 (IL-6), and tumor necrosis factor ␣ compared with DCs cultured in the presence of normal nucleosomes. Finally, DCs cultured in the presence of hyperacetylated nucleosomes were able to activate syngeneic T cells, because IL-2 production increased.Conclusion. Apoptosis-induced acetylation of nucleosomes may represent an important driving force in the development of lupus.

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 DCinduced 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 ␣ 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-␥, 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.

ObjectivesTo investigate whether T-cell activation and exhaustion is linked to HCV- and HIV disease parameters in HIV/HCV infected individuals, we studied T-cell characteristics in HIV/HCV coinfected patients and controls.Methods14 HIV/HCV coinfected, 19 HCV monoinfected, 10 HIV monoinfected patients and 15 healthy controls were included in this cross-sectional study. Differences in expression of activation and exhaustion markers (HLA-DR, CD38, PD-1, Tim-3 and Fas) and phenotypic markers on CD4+ and CD8+ T-cells were analysed by flow cytometry and were related to HCV disease parameters (HCV-viremia, ALT and liver fibrosis).ResultsFrequencies of activated CD4+ and CD8+ T-cells were higher in HIV/HCV-coinfected compared to healthy controls and HCV or HIV mono-infected individuals. Coinfected patients also showed high expression of the exhaustion marker PD-1 and death receptor Fas. In contrast, the exhaustion marker Tim-3 was only elevated in HIV-monoinfected patients. T-cell activation and exhaustion were correlated with HCV-RNA, suggesting that viral antigen influences T-cell activation and exhaustion. Interestingly, increased percentages of effector CD8+ T-cells were found in patients with severe (F3–F4) liver fibrosis compared to those with no to minimal fibrosis (F0–F2).ConclusionsHIV/HCV coinfected patients display a high level of T-cell activation and exhaustion in the peripheral blood. Our data suggest that T-cell activation and exhaustion are influenced by the level of HCV viremia. Furthermore, high percentages of cytotoxic/effector CD8+ T-cells are associated with liver fibrosis in both HCV monoinfected and HIV/HCV coinfected patients.

The etiology of the autoimmune disease systemic lupus erythematosus is not known, but aberrant apoptosis and/or insufficient clearance of apoptotic material have been assigned a pivotal role. During apoptosis, nucleosomes and several endogenous danger-associated molecular patterns are incorporated in blebs. Recent data indicate that apoptotic blebs induce maturation of myeloid dendritic cells, resulting in IL-17 production by T cells. In this review we summarize current knowledge on the role of dendritic cells in the pathogenesis of systemic lupus erythematosus with special emphasis on the uptake of apoptotic blebs by dendritic cells, and the subsequent induction of Th17 cells.

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