Initiation of antibody responses by different classes of lymphocytes. IV. Lymphocytes involved in the primary antibody response to a hapten-protein conjugate.

Thoracic duct cells and spleen cells from normal Lewis rats were tested for their ability to restore the antibody response of X-irradiated hosts to diphtheria toxoid (DTAP) or DNP-diphtheria toxoid (DNP—DT) adsorbed to alum. Although spleen cells restore a measurable response to both DTAP and DNP—DT, thoracic duct cells do not. However, thoracic duct cells from donors primed to DTAP restore the primary anti-DNP response to DNP—DT. These findings indicate that lymphocytes which initiate the antibody response to the carrier play an important role in the initiation of the primary response to the hapten coupled to that carrier. Further experiments show that the primary response of neonatally thymectomized rats to both DTAP and DNP—DT is markedly reduced as compared to that of age-matched normal rats. Thoracic duct cells can specifically restore the response of the thymectomized rats to DTAP, and, therefore, contain cells which can recognize and interact with the determinants of diphtheria toxoid. A combination of the latter cells and cells which can initiate the primary response to DNP is found in the thoracic duct lymph of normal rats. Yet, `normal' thoracid duct cells cannot restore the response to DNP—DT in irradiated hosts. These results suggest that the complete immunologically competent unit for the carrier is required for the initiation of the primary response to a hapten—protein conjugate.