Stimulation of anti‐hapten response by heterologous protein devoid of hapten

Abstract Rabbits were immunized with dinitrophenylated proteins. Injections with heterologous proteins were given 11 to 25 days after the primary injection. Spleen cell suspensions from the immunized animals were exposed to either (a) the original antigen, (b) the carrier protein of the original antigen (c) the heterologous protein used for the second injection, and (d) the heterologous protein after it was dinitrophenylated. In all the experiments a significant increase in the anti‐dinitrophenyl response was obtained, whereas no such response was obtained with proteins (or their dinitrophenylated derivatives) to which the animals were not previously exposed. The results suggest that the anti‐hapten response can be significantly augmented by immunization with heterologous hapten‐devoid proteins.