Cytotoxicity by nonimmune allogeneic lymphoid cells. Specific suppression by antibody treatment of the lymphoid cells

Studies of allograft immunity in mice. II. Mechanism of target cell inactivation in vitro by sensitized lymphocytes

The mechanisms of the in vitro interaction of sensitized lymphocytes and allogeneic target cells has been studied in a tumour allograft system in inbred mice. The cytotoxic effect of sensitized lymphocytes is shown to require the presence of Ca^{+ +} and Mg^{+ +}. Pretreatment of the lymphocytes with trypsin led to inhibition of cytotoxicity, followed by spontaneous reversal after 1–3 hours incubation. Reactivation was found to be blocked by an inhibitor of protein synthesis (cycloheximide). Cortisone was not found to inhibit the lytic interaction significantly; an occasional effect is thought to be due to toxicity of cortisone for lymphocytes as revealed by dye exclusion test. Inhibition of DNA-synthesis with FUdR (an inhibitor of the enzyme thymidine synthetase) did not reduce the lytic activity of sensitized lymphocytes.

Isologous anti-target cell sera induced in various strains of inbred mice were found to be ineffective in blocking the cellular immune reaction in vitro when directed against a minor part of the antigenic complex, but strongly inhibitory when reactive against a major part or the whole complex. Similarly, target cells lacking several of the sensitizing H-2 antigens were not lysed. An isologous anti-lymphocytic serum induced in the graft donor strain and directed against the recipient strain (lymphocyte donor) did not inhibit the cytotoxic reaction. In a heterologous system on the other hand, the lytic effect of guinea-pig lymphocytes sensitized against mouse target cells was effectively blocked by an anti-lymphocytic serum induced in mice of the graft donor strain by injection of recipient (guinea-pig) spleen cells.

Haemolytic activity of mouse peritoneal exudate cells in vitro

Mouse peritoneal exudate cells, and to a lesser degree spleen cells, can cause haemolysis of both syngeneic and allogeneic mouse red blood cells in vitro whereas lymph node and tumour cells are ineffective. The reaction was clearly detectable after 0.5–1 hour, and is usually complete after 5–6 hours at 37°. An analogous reaction was found also with sheep red blood cell targets, but haemolysis was weaker and a significant effect was not obtained until 24 hours later. The degree of haemolysis did not increase after the addition of complement. Hemolysis was not potentiated when specifically sensitized cells were employed or when PHA was present. Viability and active metabolism of the PE cell was essential for haemolysis. Only red blood cells were affected by the PE cells, nucleated target tumour cells being resistant. It was concluded that macrophages were responsible for haemolysis, which was not mediated by antibody and complement, but represented an active macrophage reaction unrelated to previously known mechanisms of haemolysis in vitro.

Graft reaction in tissue culture. 3. Effect of phytohaemagglutinin

Rat lymphocytes cultured on mouse embryo fibroblast monolayers transformed and differentiated to large pyroninophilic cells (LPC) that lysed the mouse fibroblasts. Exposure to phytohaemagglutinin (PHA), induced the development of a different type of culture culminating in a population of medium-size lymphoid cells. The sensitization of rat lymphocytes to the mouse cell antigens was blocked by adding PHA. The resulting cells were unable to lyse mouse fibroblasts. PHA, added at any time up to 72 hours after plating, also blocked sensitization; added to a population of mature LPC, it clumped the cells and markedly decreased the lytic process.

Cytotoxic effects in vitro by lymphoid cells from specifically tolerant animals

Mice of strain A were made tolerant to cells from (A×CBA)F₁ mice by neonatal injection of spleen cells. Lymphoid cells from tolerant animals carrying (A×CBA)F₁ skin grafts for 1–6 months were competent to cause destruction of both (A×CBA)F₁ and CBA fibroblast target cells in tissue culture in the presence of PHA. Normal A lymphoid cells were cytotoxic to both targets, whereas (A×CBA)F₁ lymphocytes did not kill the syngeneic F₁ targets, but were effective against the CBA fibroblasts. Lymphocytes from H-2 incompatible strains were cytotoxic to both target cell genotypes. These experiments demonstrate that the A lymphocytes in animals toleratn to (A×CBA)F₁ were effective in causing destruction of the target cells, indicating that PHA-induced cytotoxicity by incompatible cells is independent of specific immunological recognition processes.

Response to Phytohemagglutinin of Mixed Cultures of Homologous Lymphocytes from Normal Subjects and Patients with Chronic Lymphocytic Leukemia

Mixed lymphocyte cultures in the presence of PHA were performed as follows: (a) normal lymphocytes added to lymphocytes from patients with chronic lymphocytic leukemia; (b) normal lymphocytes from two unrelated subjects. In both cases, lymphocyte transformation in 72 h cultures was often lowered if compared with the values expected according to the sum of the responses to PHA of both partners. Such a decrease is consistent with an interference between the transforming effect of PHA and the stimulation due to the histoincompatibility of the cultured cells. The possibility that in some cultures the two stimulations may result in additional effect is discussed.