Immunoglobulin C-gene expression. I. The commitment to IgG subclass of secretory cells is determined by the quality of the nonspecific stimuli.

Polyclonal stimulation of normal splenic B lymphocytes with either lipopolysaccharide (LPS) or helper T lymphocytes specific for B cell surface antigens results in the selective expression of IgG subclasses by the secretory cells: in addition to IgM-secreting plaque-forming cells (PFC), thymus-independent stimulation leads to the development of IgG2 and IgG3 PFC, while helper cell-dependent activation leads to IgG1 and IgG2 PFC. This cannot be solely explained by selective stimulation of distinct B cell subpopulations, because purified LPS-reactive blasts if restimulated by helper cells switch to IgG1 while if maintained with LPS switch to IgG3. The simultaneous stimulation of splenic B cells with LPS and helper cells results in additive IgM and IgG2 responses, but in the selective suppression of IgG3 PFC with a concomitant synergic enhancement of IgG1 responses. These results are interpreted to indicate that the expression of IgG C genes in proliferating B lymphocytes is directed by the quality of nonspecific stimuli.