Studies on cell-mediated immunity to lymphocytic choriomeningitis virus in mice.

A large amount of experimental evidence has already been presented indicating the great importance of the cell-mediated immunity in the pathogenesis of the LCM virus infection in mice. In this laboratory a method which makes it possible to measure this cellular immunity quantitatively in vitro has been developed. The method is based on the determination of the radioisotope released after the interaction between specifically sensitized lymphocytes and syngeneic (1)Cr-labeled LCM virus-infected target cells. By using this technique the time-course of the cell-mediated immunity has been established in acutely infected mice and in virus carriers adoptively immunized with syngeneic sensitized lymphocytes. Lymphocytes from acutely infected mice showed a strong lysing effect on the target cells, with a sharp maximum at about the 9th day after infection. The cell-mediated immunity in adoptively immunized virus carrier mice showed the same time-course, but in these animals the lytic effect of the lymphoid cells was considerably less pronounced. Lymphocytes from untreated virus carriers did not, however, have any effect on the target cells, and in these animals it was not possible to demonstrate any evidence of enhancing antibodies, In experiments employing serial dilutions of sensitized lymphocytes in normal cells a direct linear relationship between the number of sensitized lymphocytes and target cell destruction was found. These experiments seem to indicate that the underlying mechanism in the cytotoxic reaction is a direct cell-to-cell interaction.