A comparison of thymus dependent and thymus independent antibody responses made by different numbers and populations of immunocompetent cells.

Mice pretreated with cyclophosphamide were reconstituted with syngeneic cells. Their response to pneumococcal polysaccharide type III (S III) was considered to measure the activity of transferred B cells and the response to sheep or horse erythrocytes (SRBC and HRBC) that of B and T cells. The populations of donor cells used contained different proportions of T and B cells; their response to S III ranked in the order, spleen from thymectomized donors > normal spleen > lymph node; the reverse obtained in the responses to erythrocytes. Thus, lymph node suspensions made the most antibody to thymus dependent antigens though they contained the least B cell activity. It is concluded that T cells, rather than initiating, amplify the response of B cells to these antigens. Spleen cells were used to obtain dose response curves for each antigen. A ten-fold increase in cell dose increased the response to S III three-fold, to SRBC ten-fold, and to HRBC twenty-fold or more. These differences follow if amplification of the B cell response increases with T cell dose, and is greater for HRBC than SRBC. It is argued that agents which alter the proportions of B and T cells equally, may not affect thymus dependent and independent responses equally.