Enhancement and suppression of immunoglobulin G-producing B cells in the presence of immune T cells.

Mice were immunized one to three times with sheep red blood cells. Four to seven days after the last immunization, the spleens were removed and the cells were cultured in vitro in the absence of antigen. Removal of most T cells by anti-θ serum treatment prior to culture could increase the number of IgG-producing B cells without affecting the number of specific or nonspecific IgM-producing B cells detected after 2 days of culture. Addition of graded numbers of immune cells to pure immune B cells enhanced the number of IgG-producing B cells, whereas addition or higher number of immune cells caused suppression. Since removal of T cells could also enhance the proliferation of IgG-producing B cells induced by lipopolysaccharide (LPS), a polyclonal B-cell activator, it is suggested that the suppressive effects of high numbers of immune T cells are exerted directly on the B cells.