Protective reaction against malaria infection in mice sensitized with Frozen-thawed toxoplasma tachyzoites.

Mice sensitized with frozen-thawed Toxoplasma antigen emulsified in Freund's Incomplete Adjuvant (FIA) showed high resistance against Plasmodium berghei infection, but not in mice sensitized with paraformaldehyde-fixed. Toxoplasma or saline plus FIA. However, mice which survived from malaria infection did not show any protective reaction against the RH strain inoculation. Furthermore, an immune interferon activity was detected in the supernatant of the spleen cells collected from the mice sensitized with frozen-thawed Toxoplasma and cultured with the specific antigen, however, no Toxoplasma growth inhibitory factor (Toxo-GIF) was found in the same supernatant of lymphokines. From these results, it is suggested strongly that frozen-thawed Toxoplasma antigen could confer nonspecific resistance in mice against Plasmodium infection.