MCA1 detection of histone H3 serine 10 phosphorylation, a novel biomarker for determination of mitotic indices.

Previously we identified circulating autoantibodies in high titre in the serum of a patient with biopsy-proven discoid lupus erythematosus reactive to serine/threonine phosphoepitopes of the novel mitotic chromosomal autoantigen we named MCA1. MCA1-reactive antibodies have subsequently been demonstrated to bind to the modified histone H3 (H3K9me3S10ph). In this study we utilised Epstein Barr virus (EBV) infection of peripheral blood mononuclear cells collected from this patient to immortalise B-lymphocytes producing MCA1-reactive antibodies. We found MCA1-reactive antibody production by the EBV-immortalised B-lymphocytes unstable in culture. We discuss the possibilities of producing MCA-1-reactive reagents through protein engineering methods (variable or complementarity-determining region grafting) and to modulate antibody affinity through library technologies (such as phage, yeast or ribosome display). Clinical studies have shown that carcinogenesis is most often linked to the development of proliferative abnormalities and proliferative activity has prognostic significance in a variety of human tumours. Here we demonstrate the potential utility of antibodies reactive to H3K9me3S10ph (MCA1), which is only detected on mitotic chromatin, as a marker for cell proliferation in FACS analysis, tissue section staining and in determination of mitotic indices.