Down-regulatory role of surface CD4 molecules on autoreactive helper T cells during B cell activation

MS202 is an IL-2-dependent Th2 clone reactive to auto-MHC class II antigens as previously reported. It expresses CD4, TCR-alphabeta, Thy 1.2 and H-2k on the cell membrane, as well as CD40 ligand. In order to investigate a functional role of surface CD4 molecules on Th2 cells during B cell activation, we attempted to establish a CD4- variant subclone derived from the CD4+ MS202, and its effect on B cell activation was examined. Briefly, MS202 was incubated with ethyl methanesulfonate to induce mutation followed by extensive treatment with anti-CD4 MoAb and complement. MS1.1.2, a representative subclone of resulting cell lines, was shown to lack CD4 molecules on the cell membrane, although it possessed almost the same amount of surface molecules other than CD4 compared with the original MS202 by analysis with flow cytometry. Interestingly, MS1.1.2 induced the maturation of B cells into IgM-producing cells more potently than MS202. This differentiative effect was markedly greater on activated B cells than resting B cells; each population was prepared from splenic B cells by a gradient separation method, but after treatment with anti-IgM antibodies, resting B cells responded to MS1.1.2, resulting in the secretion of a comparative amount of IgM. Furthermore, the effect of MS 1.1.2 on DNA synthesis of activated B cells was much greater than that of MS202. The present results suggest that surface CD4 molecules on Th2 cells may not be substantially required for B cell activation, and rather mediate a down-regulation signal to B cells.