Specific post-translational histone modifications of neutrophil extracellular traps as immunogens and potential targets of lupus autoantibodies
1 Department of Medicine, Division of Immunology and Rheumatology, Stanford School of Medicine, 269 Campus Drive, Stanford, California 94305, USA
2 Center for Immunology, University of Minnesota Medical School, 420 Delaware Street SE, Minneapolis, Minnesota, 55455, USA
3 Department of Medicine, Division of Oncology and of Hematology, Stanford School of Medicine, 300 Pasteur Drive, Stanford, California 94305, USA
4 Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA 94305, USA
Arthritis Research & Therapy 2012, 14:R25 doi:10.1186/ar3707Published: 2 February 2012
Autoreactivity to histones is a pervasive feature of several human autoimmune disorders, including systemic lupus erythematosus (SLE). Specific post-translational modifications (PTMs) of histones within neutrophil extracellular traps (NETs) may potentially drive the process by which tolerance to these chromatin-associated proteins is broken. We hypothesized that NETs and their unique histone PTMs might be capable of inducing autoantibodies that target histones.
We developed a novel and efficient method for the in vitro production, visualization, and broad profiling of histone-PTMs of human and murine NETs. We also immunized Balb/c mice with murine NETs and profiled their sera on autoantigen and histone peptide microarrays for evidence of autoantibody production to their immunogen.
We confirmed specificity toward acetyl-modified histone H2B as well as to other histone PTMs in sera from patients with SLE known to have autoreactivity against histones. We observed enrichment for distinctive histone marks of transcriptionally silent DNA during NETosis triggered by diverse stimuli. However, NETs derived from human and murine sources did not harbor many of the PTMs toward which autoreactivity was observed in patients with SLE or in MRL/lpr mice. Further, while murine NETs were weak autoantigens in vivo, there was only partial overlap in the immunoglobulin G (IgG) and IgM autoantibody profiles induced by vaccination of mice with NETs and those seen in patients with SLE.
Isolated in vivo exposure to NETs is insufficient to break tolerance and may involve additional factors that have yet to be identified.