SELECTION OF A STRAIN OF ALBINO MICE REFRACTORY TO PLASMODIUM BERGHEI INFECTION.

Some features of the natural history of malaria in holoendemic areas can be explained by the presence of acquired immunity. There is also evidence that transmission of humoral antibodies in utero from the immune mother plays some part in the transient protection of the offspring. Little is known about the importance of a genetic factor.The possibility of inheritance of immunity to malaria was investigated on six generations of a strain of white mice originating from 50 parents fully susceptible to infection with Plasmodium berghei. These mice were interbred in such a way that each generation was exposed to an infection attenuated by chloroquine. The survivors were mated with a view to selecting a strain with a decreased susceptibility to infection. Some 16% of mice in the sixth generation and one animal out of four in the seventh were able to resist the initial inoculation with 0.1 million parasites. By the sixth generation, there was evidence of reduction of the period of primary parasitaemia and lengthening of the prepatent period, suggesting that some selection of animals with greater tolerance had occurred. A decrease of fertility, particularly obvious in the seventh generation, limited the number of surviving animals and the experiment had to be discontinued.