Microbicidal activity of toxoplasma immune beagle plasma and lymphokines to toxoplasma multiplication in host cells

In beagles infected with Toxoplasma tachyzoites, IgM and IgG humoral antibodies appeared on the early period of infection as the expression of the humoral antibody response. IgM antibody was no longer observed after 16 days, however, IgG antibody persisted maintaining high titers up to the last day of the experiment. When challenged on the 13th day postinfection, IgG antibody levels were boosted, however, IgM levels did not show any change at all. Lymphokines obtained from spleen cells collected 10, 30, 100 and 300 days postinfection showed a gradual increase in the ability to inhibit Toxoplasma multiplication in normal canine monocytes accordingly compared to the control which showed no inhibition at all. Toxoplasma lysate antigen was injected intravenously to hyperimmuned dog 2 wk after rechallenge. Plasma collected 24 hr after injection inhibited markedly Toxoplasma multiplication. No change in the microbicidal activity was found when plasma was absorbed with anti-canine IgG compared to the unabsorbed one. The results therefore indicated that the substance inhibiting Toxoplasma multiplication in canine monocytes existing in plasma is not derived from antibodies specific for Toxoplasma but as a Toxoplasma growth inhibitory factor (Toxo-GIF) or a similar substance. The plasma obtained also showed antiviral activity of interferon type II and was found to increase in the circulation 6 hr after Toxoplasma lysate antigen injection.