Effects of gamma interferon on syntheses of DNA and proteins by Entamoeba histolytica

To define the participation of cell-mediated immunity in resistance to amebic infection through the action of soluble mediators or lymphokines (LKs), including gamma interferon (IFN-gamma), we studied their effect on Entamoeba histolytica. Supernatants from cultures of lymphoid cells, which had been stimulated in vitro with concanavalin A and were rich in lymphokines (LRSNs), and recombinant IFN-gamma were used. LRSN and recombinant IFN-gamma inhibited the growth of E. histolytica trophozoites in vitro. These LKs did not show a cytotoxic effect on the ameba, but they did inhibit rather significantly protein and DNA syntheses of the protozoa. Interestingly, LRSN incubated at 4 degrees C in the presence of trophozoites lost the ability to inhibit the replication of vesicular stomatitis virus. IFN-gamma inactivated at pH 2 had no effect on DNA synthesis by the ameba, thus suggesting that IFN-gamma is responsible for the observed inhibition of parasite growth. Furthermore, the IFN-gamma inhibitory effect was abolished by a monoclonal antibody specific for this LK. The results suggest that IFN-gamma may participate in protection against amebiasis infection through the activity of mediators released by lymphocytes during infection.