Figure 1. Determination of the radiation dose necessary to attenuate blood-stage Pb-A parasites.

Virulent Pb-A parasitized RBC (pRBC) were exposed to increasing doses of gamma irradiation (10, 20, 40, 60, 80, 100 kilorads). 10⁷ irradiated pRBC or non-irradiated control pRBC (Ctrl) were injected intravenously (iv) into groups of naïve CD1 mice and parasitemia was monitored by blood smear. The graph shows the percentage of mice without patent parasitemia in each group over time beginning with day 2. Data are pooled from 3 experiments. Groups of mice infected with control pRBC or with pRBC exposed to 10, 20, 40, or 60 krad irradiation all developed patent parasitemia by day 7 (n = 4 mice each group). Accordingly, the curves describing these groups approach 0% by day 7. 70% (10/14) of mice infected with 80 krad irradiated pRBC remained free from patent blood-stage disease by day 14 (open circles, dashed line). 100% (10/10) of the mice injected with 100 krad irradiated pRBC remained free from blood stage infection under the period of observation (open squares, solid line). 100 krad irradiation was chosen as the attenuating dose in subsequent experiments.