Antigen-specific and nonspecific mediators of T cell/B cell cooperation. V. Unresponsiveness to HGG in vitro of these two T cell subpopulations.

In previously published experiments we have distinguished two subpopulations of helper T cells (specific helper and nonspecific helper) in the spleens of antigen-primed mice. These subpopulations can be differentiated by their modes of action, and their activities and dose-response characteristics in mouse spleens primed with human gamma-globulin (HGG). In experiments designed to test shether the two subpopulations were derived from the same pool of precursors, or different pools, mice were injected with limiting doses of a tolerogenic form of HGG. They were subsequently challenged with an immunogeneic dose of HGG and their spleens assayed for specific helper and nonspecific helper activities in response to HGG in vitro. Over the dose range of tolerogenic HGG studied, both the helper activities were found to be equally tolerized. The question of the possible involvement of suppressor T cells in the maintenance of the state of unresponsiveness was also addressed quantitatively by the use of this model system. No active suppression was demonstrable in the maintenance of tolerance in either T cell subpopulation. These results suggest that the two types of helper T cells are derived from a common precursor pool, or from different pools with identical susceptibilities to tolerogen. Suppressor cells do not appear to play a role in this form of tolerance.