Epigenetic histone code and autoimmunity.

The multiple inter-dependent post-translational modifications of histones represent fine regulators of chromatin dynamics. These covalent modifications, including phosphorylation, acetylation, ubiquitination, deimination, and methylation, affect therefore the numerous processes involving chromatin, such as replication, repair, transcription, genome stability, and cell death. Specific enzymes introducing modified residues in histones are precisely regulated, and a single amino acid residue can be subjected to a single or several, independent modifications. Disruption of histone post-translational modifications perturbs the pattern of gene expression, which may result in disease manifestations. It has become evident in recent years that apoptosis-modified histones exert a central role in the induction of autoimmunity, for example in systemic lupus erythematosus and rheumatoid arthritis. Certain histone post-translational modifications are linked to cell death (apoptotic and non-apoptotic cell death) and might be involved in lupus in the activation of normally tolerant lymphocyte subpopulations. In this review, we discuss how these modifications can affect the antigenicity and immunogenicity of histones with potential consequences in the pathogenesis of autoimmune diseases.