Immunization against rodent malaria with cryopreserved irradiated sporozoites of Plasmodium berghei.

The preparation and storage of Plasmodium berghei sporozoites for immunization purposes is described. The sporozoites were harvested from the salivary glands of infected mosquitoes, and maintained in cold tissue culture medium M199 with or without mouse serum. They were irradiated and frozen either at -75 degrees C or in liquid nitrogen. After various periods sporozoites were thawed and injected into A/J mice. At the end of the immunization period the animals were challenged with infective sporozoites of P. berghei and monitored for parasitemia. It was found that the storage did not appreciably alter the ability of the irradiated sporozoites to induce protective immunity in the recipient animals. The highest protection (80--100%) was induced with sporozoites maintained in 10% serum and stored at -75 degrees C.