Requirement for interactions between two subpopulations of T cells for helper cell induction in vitro

The evidence for the interaction of 2 subpopulations of T cells, short-lived cells sensitive to adult thymectomy (T1 cells), and long-lived recirculating cells, sensitive to the action of antilymphocyte serum (T2 cells) in the induction of helper cells is presented. This T-T interaction occurred across a cell-impermeable nucleopore membrane, indicating that it did not depend on cell contact, but was mediated by subcellular factors. There was no genetic restriction on this T-T interaction, if it was performed across a nucleopore membrane. The implications of these results on our concepts of the mechanism of help are discussed.