[Functional analysis of an autoantigen reactive B cell clone derived from MRL/MP-lpr/lpr mice]

MRL/MP-lpr/lpr (MRL/lpr) mice are known to provide a good model for the study on the pathogenesis of systemic lupus erythematosus with massive involvement of abnormal T lymphocytes in the spleen and lymphonodes. However, a direct role of B cells of MRL/lpr mice in autoimmune responses is not clear until this time. In the present study, to investigate the characteristic of B cells of the mice, we tried to establish a B cell clone after hybridization between splenic B cells of these mice and 2.52 M, a HAT selective medium sensitive mutant B cell line in the presence of polyethylene glycol and dimethyl sulfoxide and examined its response to autoantigens. MRL27.4, a subclone of a resulting hybridoma, expressed IgM, B220, IKk, ICAM-1, and LEA-1 on the cell membrane as well as CD5 molecules by analysis with flow microfluorometory (FMF). Also, MRL27.4 was shown to exhibit rosette formation against blood cells treated with bromelain (Br-RBC) at a frequency of more than 95%, and to express DNA-receptor (DNA-R) on its surface by FMF analysis with biotin-labeled ssDNA. In contrast, the parental 2.52 M did not form rosettes with Br-RBC and the expression of DNA-R on the cell membrane of 2.52 M was significantly less compared with that of MRL27.4. Interestingly, MRL27.4 produced a high titer of IgM-anti-ssDNA antibodies and IL-6 after treatment with the purified RBC membrane or immobilized DNA. On the other hand, the parental 2.52 M neither produce IgM-anti-ssDNA antibodies nor IL-6 under the same conditions. The results suggest that MRL27.4 is an autoantigen reactive B cell clone derived from MRL/lpr mice and its surface DNA-R, by itself, function to autoantigens. In this process, there might be an autocrine network mediated by IL-6. In conclusion, MRL27.4 provides a good model for the study on the direct function of B cells of MRL/lpr mice during abnormal immune responses to autoantigens.