Comparison of the properties of antirickettsial activity and interferon in mouse lymphokines

Certain properties of the antirickettsial activity and interferon in lymphokine preparations obtained from concanavalin A-stimulated mouse spleen cells were compared. Both the antirickettsial activity and interferon were relatively stable to heating at 56 degrees C, whereas both activities were destroyed by trypsin, by heating at 80 degrees C, or by exposure to pH 2 for 24 h. Both activities were likewise inhibited after incubation with rabbit antisera to partially purified murine interferon-gamma. In contrast to the mouse lymphokine preparations, which contained both interferon-gamma and antirickettsial activity, a preparation of virus-induced interferons (type I) had no detectable antirickettsial activity. Human foreskin fibroblasts, which were not sensitive to the antirickettsial activity in mouse lymphokines, acquired the ability to inhibit rickettsial growth when they were cocultured with sensitive mouse L929 cells treated with mouse lymphokines. These results are consistent with the idea that the antirickettsial activity in mouse lymphokines is due to interferon-gamma.