Mechanism of B-cell activation and paralysis by thymus-independent antigens. Additive effects between NNP-LPS and LPS in the specific response to the hapten.

Normal spleen cells showed a bell-shaped dose response profile when stimulated in vitro with the thymus-independent antigen (4-hydroxy-3,5-dinitrophenyl)acetyl (NNP)-lipopolysaccharide (LPS) with regard to the development of high-avidity plaque-forming cells to NNP. The addition of suboptimal concentrations of LPS to cultures stimulated by suboptimal concentrations of NNP-LPS resulted in optimal induction of B cells in that affinity fraction. Addition of LPS to cultures optimally stimulated by NNP-LPS resulted in paralysis of the specific cells. These results are interpreted in terms of the additive effects between the mitogenicity of LPS and the mitogenicity of NNP-LPS, the latter being selectively focused on the specific cells, thus providing further evidence for the 'one nonspecific signal' hypothesis for immune activation of B cells.