Alloreactive and H-2-restricted Lyt 23 cytotoxic T lymphocytes derive from a common pool of antecedent Lyt 123 precursors

If the collaborative requirement of Lyt 1 T helper cells is bypassed by the Lyt 1 T cell-derived mediator of T help, termed I1-2, upon antigenic stimulation, PNA⁺ Lyt 123 thymocytes differentiate into either alloreactive or H-2-restricted PNA^- Lyt 23 cytotoxic effector cells. Along the differentiation pathway from Lyt 123 → 23 effector cells, cytolytic activity is carried out by T cells that still express the Lyt 123 phenotype. The data establish that Lyt 23 CTL are produced by differentiation from antecedent Lyt 123 cells.