Rabbit lymphocyte populations responding to haptenic and carrier determinants for DNA synthesis

Mesenteric lymph node cells from rabbits primed with dinitrophenyl derivative of either Ascaris extract (DNP-Asc) or ragweed fraction D (DNP-Rag) were stimulated by the priming antigen, free homologous carrier, or with the hapten conjugated with rabbit serum albumin (DNP-RSA), and increase in DNA synthesis was observed by 3H-thymidine incorporation. The results showed that both free carrier and DNP-RSA stimulated DNA synthesis. The response of the primed lymph node cells to DNP-homologous conjugate was slightly higher than that to free carrier, but the optimal concentration of both antigens for maximal thymidine incorporation was 10 to 100 mug/ml. This concentration was about 100 times higher than the optimal concentration of the same antigens for maximal antibody response in vitro. The DNA synthetic response to DNP-RSA was much less than that obtained by free carrier, and the optimal concentration of DNP-RSA for the response was comparable to the concentration of DNP-homologous carrier conjugate to induce maximum anti-DNP antibody response. The relative importance of immunoglobulin bearing (B) cells and T cells in the DNA synthetic responses was assessed by fractionating lymph node cells with antigen-coated or anti-immunoglobulin coated cellular immunosorbent. The results indicated that hapten-specific, immunoglobulin-bearing cells (B cells) are responsible for the DNA-synthetic response to DNP-RSA, whereas B cells play a minimal role in the response to free carrier.