FIGURE 4.

Protection induced by vaccination with Py-iRBC followed by chloroquine treatment is mediated by IFN-γ. A, Concentrations of IFN-γ in the sera collected 42 h after challenge with 2500 sporozoites, from control mice or mice immunized with 10⁶ Py-iRBC or normal RBC under 10-day chloroquine cover starting on the day of immunization. Sera were collected 42 h after challenge with 35,000 sporozoites. Results are expressed as mean ± SEM of n = 5 mice. *, p < 0.05 vs control mice using ANOVA followed by Tukey’s test. B, Groups of BALB/c mice were injected with 10⁶ Py-iRBC treated with chloroquine from day 0 to 10 starting the day of Py-iRBC inoculation. They were challenged i.v. with 4000 sporozoites at least 15 days after the last chloroquine injection. Immunized mice were injected with the rat Abs control rat IgG or anti-IFN-γ. Data are cumulative results of two experiments with n = 4–5 mice per experiment. All control mice treated with chloroquine alone (n = 10) developed patent blood stage parasitemia after sporozoite challenge. Protection was defined as the percentage of the mice that did not develop patent blood stage over 10 days postchallenge in the group that were challenged by sporozoites. **, p <0.05 between immunized mice treated with rat IgG immunized mice treated with anti-IFN—γ Abs, for values on day 10, as calculated by Fisher’s exact test. Number in brackets represents the percentage of protection.