Specificity of rheumatoid synovial B-cell hybridoma with germline configurated IGVH genes against human nuclear protein histone

B cells (plasma cells and B-lymphocytes) belong to the dominant part of the inflammatory infiltrate in RA synovitis. To disclosure the nature of antigens involved in the triggering and the perpetuation of the disease we carried out the study of IgG, a monoclonal B-cell hybridoma, belonging to the VH3 family (DP 43), from rheumatoid synovial membrane, produced by electrofusion and without prior in vitro stimulation. The subject of the study was an RA patient with definite and active RA, featuring dense inflammatory infiltration with the occurrence of secondary lymphatic follicles in the affected joint. This hybridoma was analysed by PCR, immunohistology, immunoprecipitation and western blot, and the results were correlated with pathological data and parameters of local disease activity. By PCR we found out that this hybridoma had germline configuration IgVH genes with R/S ratio = 1; it revealed specific binding (20 kDa) to nuclear extract of fibroblasts cell line (Hep2), later identified by mass spectrometry as the nuclear protein human histone (1B, 1C, 1D). Being this protein an exclusive nuclear protein involved in the chromatin condensation, it can be assumed that its implication in RA will be related to the perpetuation of the disease and inflammation after massive cell death, due to destruction of the joint tissues.