Potentiation of the PFC Response to Thymus-Independent Antigens by Heterologous Erythrocytes

Immunization with horse erythrocytes (HRBC) and a thymus-independent (TI) antigen of the TI-2 category, such as a native dextran, dinitrophenyl-dextran (DNP-dextran), or DNP-Ficoll, resulted in a three- to four-fold enhancement of the plaque-forming cell response to the TI antigen. The effect was found to be T-cell associated, since cyclosporin A abrogated enhancement. The T cells of T-cell factor involved were elicited early in the response to HRBC and acted on the initial stages of the TI response. The HRBC-induced potentiation affected only B cells activated by the TI antigen; it could not induce a TI response when TI-2 antigen was given under nonresponsive conditions; and it had only a slight effect on the response to a thymus-dependent (TD) antigen. A soluble TD antigen, bovine serum albumin-coupled dextran (BSA-dextran), did not have potentiating ability equivalent to that of the particulate HRBC. It was concluded that non-specific T-cell help can influence TI-2 responses when they are present simultaneously.