Ability of tolerized Th1 and Th2 clones to stimulate B cell activation and cell cycle progression

Abstract

Tolerant and nontolerant murine Th1 and Th2 clones, specific for human γ-globulin (HGG), were compared for their ability to promote cell cycle entry and progression by B cells in vitro. When stimulated with HGG, nontolerant Th1 and Th2 clones induced similar increases in B cell membrane MHC class II levels—a phenomenon associated with early B cell activation. Nontolerant Th1 and Th2 clones also induced B cell DNA synthesis, an event associated with subsequent G 1 phase traversal, although Th2 cells were more efficient than Th1 cells in stimulating this activity. Exposure of Th clones to tolerogen in the form of HGG-pulsed chemically fixed APC inhibited the ability of Th1 clones, but not Th2 clones to promote polyclonal B cell DNA synthesis in HGG-stimulated secondary cultures. However, Th1 clones exposed to tolerogen did not lose their ability to increase the expression of MHC class II molecules on B cells in these cultures. These results indicate that tolerance induction does not inhibit the ability of Th1 clones to promote early activation of B cells but does inhibit the mechanism by which Th1 clones promote B cell cycle progression. In contrast, exposure of Th2 cells to tolerogen does not inhibit significantly the ability of these cells to stimulate B cell cycle entry or progression.