Requirement of parental T lymphocytes for the in vitro induction of F1 hybrid anti‐parent cytotoxicity

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Abstract
Primary F1 anti‐parent cell‐mediated lympholysis (CML) is a specific response generated in mixed cultures by F1 T lymphocytes with the aid of macrophage‐like cells of responder and stimulator type. A model was described in which the induction of this response required T lymphocytes among stimulators, as judged by the lack of induction following T cell depletion of parental cells by (a) separation on nylon wool columns, (b) treatment with anti‐Thy‐1 antiserum and complement, (c) treatment of donor mice with rabbit anti‐mouse thymocyte serum, or (d) congenital absence of the thymus in nu/nu donors. The parental T lymphocytes required were relatively mature, as indicated by resistance to cortisone, persistence after adult thymectomy, and sensitivity to xenogeneic anti‐thymocyte antiserum. T‐deprived cell populations retained the ability to induce allogeneic CML.Parental lymphoma cells, spleen cells stimulated by mitogens for T or B lymphocytes, normal cells of central and peripheral lymphoid organs, and peritoneal exudate cells, all served to a varying extent as targets for anti‐parent cytotoxic effectors (CTL), but there was no close correlation with their ability to serve as stimulators. Spleen or peritoneal exudate cells of athymic mice were capable of serving as “antigenic” targets for specific F1 anti‐parent CTL, and yet failed to induced the response. Thus, the role of parental T cells in the induction of F1 anti‐parent cytotoxicity was not that of bearing the “antigen”. It was concluded that irradiated parental T lymphocytes provided back stimulation to F1 hybrid responders, either directly or indirectly via the activation of macrophage‐like cells. Under certain circumstances, however, the requirement for parental T cells can be circumvented.