Stimulation in vivo and in vitro of Anti-Dinitrophenyl Antibodies with Homologous Protein Carriers Devoid of Hapten

Abstract Rabbits were immunized with dinitrophenyl-protein conjugates in complete Freund's adjuvant. After 2 to 4 weeks single cell suspensions were made from the spleens of these animals and cultured in vitro. A positive anti-dinitrophenyl secondary response was obtained in these cultures upon subsequent exposure to either dinitrophenyl-homologous protein carrier or homologous carrier alone. No response was obtained after addition of either dinitrophenyl-heterologous protein conjugate or unrelated protein. A positive response was indicated by an increase in cell proliferation, appearance of specific antibody-producing cells, and formation of soluble antibodies upon addition of antigen. Moreover, in vivo boosting with carrier protein alone of rabbits which had been previously immunized with dinitrophenyl-protein conjugate resulted in increased production of antibodies with a specificity for the dinitrophenyl hapten. Analysis of the antibodies produced by the rabbits immunized with hapten-protein conjugates revealed that a certain proportion of them were directed towards “shared” determinants, i.e., determinants partially composed of the hapten group and partially of the protein carrier in the vicinity of hapten attachment. The carrier boosting effect observed in the in vitro and in vivo experiments appeared to be due to stimulation of cells producing antibodies with such “shared” determinants.