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

Tolerant and nontolerant murine Th1 and Th2 clones, specific for human gamma-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 G1 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 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.