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.