Antigenic variation in Plasmodium chabaudi: analysis of parent and variant populations by cloning.

Nineteen of 22 recrudescent populations of Plasmodium chabaudi AS strain were found to be significantly less sensitive to the protective activity of pools of immune serum, than the parent population from which they were derived. The immune sera were collected from donor mice which had been infected with the parent population and had just reduced the patent primary parasitaemia to subpatent levels. Clones prepared from the parent population (which had previously been cloned) and recrudescent variant populations were tested for their sensitivity to the immune sera. It was found that all the clones from the parent population were sensitive to the immune sera but some were more sensitive than others and that a recrudescent variant population could include both sensitive and insensitive parasites. Two insensitive clones of the recrudescent population were found to be different from each other.