Kinetic analysis of a graft reaction induced in cell culture.

A kinetic analysis was made of the graft reaction induced in culture by plating rat lymphocytes on monolayers of mouse fibroblasts. The immune cytolysis of the mouse fibroblasts, carried out by sensitized rat large pyroninophilic cells (LPC), was determined by the rate of Cr released from labelled target cells. The sensitivity and accuracy of the quantitative method employed in the present study was evident from: (a) the low spontaneous release of the Cr from the labelled fibroblasts, (b) the lack of re-utilizaiton of the released Cr by lymphocytes, and (c) the low standard deviation of replicate plates. Experiments were made to determine the order of the lytic reaction with regard to the different cell reactants (LPC and fibroblasts). When the rate of lysis was measured while constant numbers of LPC interacted with different concentrations of fibroblasts, the reaction was of first order for fibroblasts. When measured while constant numbers of fibroblasts interacted with different concentrations of LPC—the reaction was of first order for LPC. This indicates that one LPC is required to lyse one fibroblast. The kinetic analysis of the lytic reaction also indicated that each fibroblast dies independently as a result of a single hit by a LPC. There was no latent period, or only a very short one, for the lytic effect. Thus, the lytic process of a target cell starts as soon as cell-contact between LPC and fibroblast is accomplished. The number of LPC is not decreased during the lytic reaction. Hence, LPC are not subjected to an `allergic death' after exerting a lytic effect on target cells.