FIG 5.

Immunization with irradiation-attenuated hemocoel sporozoites. (A) C57BL/6 mice were immunized three times at weekly intervals with 10,000 irradiated sporozoites (10k y-SPZ), isolated either from mosquito salivary glands (blue) or from the hemocoel (red). All animals were challenged with 10,000 salivary gland sporozoites (10k SPZ) 18 days after the last immunization. After 42 h, the livers were removed, and the parasite loads were quantified by real-time RT-PCR (n = 5 each; *, P < 0.05; **, P < 0.01 [Mann-Whitney test]). (B) Kaplan-Meier analysis of C57BL/6 mice that were immunized as described above. Challenge was performed either 15 days (day 29; short-term protection) or 51 days (day 65; protracted protection) after the last immunization by intravenous injection of 10,000 salivary gland sporozoites. Blood parasitemia was determined by daily microscopic examination of Giemsa-stained blood films (n = 5 for all experiments). Analysis by Kruskal-Wallis test revealed nonsignificant differences for protracted protection but P < 0.01 (**) for short-term protection.