Identification of new pathogenic players in lupus: autoantibody-secreting cells are present in nephritic kidneys of (NZBxNZW)F1 mice.

An important hallmark of systemic lupus erythematosus is the production of autoantibodies specific for nuclear Ags, among which nucleosomes and their constituents, DNA and histones. It is widely admitted that some of these autoantibodies contribute largely in lupus pathogenesis because of their nephritogenic potential. However, the underlying mechanisms are still debated. In this study, we analyzed the autoimmune response against histone H2B during the course of the disease in lupus-prone (NZBxNZW)F1 mice, both in lymphoid organs and kidneys, and we assessed its potential involvement in lupus pathogenicity. We found that the N-terminal region of histone H2B represents a preferential target for circulating autoantibodies, which kinetics of appearance positively correlates with disease development. Furthermore, immunization of preautoimmune (NZBxNZW)F1 mice with H2B peptide 1-25 accelerates the disease. Kidney eluates from diseased (NZBxNZW)F1 mice do contain IgG Abs reacting with this peptide, and this H2B sequence was found to be accessible to specific Ab probes in Ag-containing deposits detected in nephritic kidneys. Finally, compared with control normal mice and to young preautoimmune (NZBxNZW)F1 animals, the frequency of cells secreting autoantibodies reacting with peptide 1-25 was significantly raised in the spleen and bone marrow and most importantly on a pathophysiological point of view, locally, in nephritic kidneys of diseased (NZBxNZW)F1 mice. Altogether our results demonstrate the existence in (NZBxNZW)F1 mice of both a systemic and local B cell response targeting the N-terminal region of histone H2B, and highlight the potential implication of this nuclear domain in lupus pathology.