Transforming growth factor-beta induced class switch recombination may be modified during the cell proliferation...

Mouse spleen cells were stimulated, first by transforming growth factor beta (TGF-beta) and then by interleukin-2 (IL-2) in the presence of bacterial lipopolysaccharide (LPS). LPS plus IL-2 stimulation restored the cell proliferation suppressed by TGF-beta and increased the number of B cells. Both TGF-beta alone or TGF-beta plus IL-2 enhanced production of surface IgA-positive (sIgA+) cells in LPS-stimulated B-cell cultures. We characterized extrachromosomal circular DNAs generated in TGF-beta-primed and IL-2-stimulated B cells and identified the breakpoints of S mu/S gamma 3 recombinants which were the major intermediates of S mu and S alpha switch recombination. All switch recombination sites were dispersed evenly within both S mu and S gamma 3 regions. This even distribution of S mu/S gamma 3 breakpoints is in contrast to the site preference of class switch breakpoints induced by TGF-beta alone. These results suggest that IL-2-stimulated cell proliferation may modify class switch recombination primed by TGF-beta.