The effect of mosquito transmission of antigenic variants of Plasmodium chabaudi.

Plasmodium chabaudi AS strain in mice is characterized by an acute primary parasitaemia, and one or more less acute recrudescences. Previous work has shown, using a passive protection assay, that the recrudescent parasites are usually antigenically different from parasites of the parent population with which the mice were first infected. In this study the effect of mosquito transmission on the antigenic expression of recrudescent populations of P. chabaudi was examined. In the first experiments the recrudescent population which was antigenically different from the parent population was uncloned. After transmission through Anopheles stephensi the recrudescent population appeared to revert to an antigenic type similar to that of the parent population. In the second experiment clones from a recrudescent population were mosquito transmitted and again the parasites of the primary patent parasitaemia in the mice, bitten by the infected mosquitoes, had reverted to the parental type. It is suggested that antigenic variants of P. chabaudi AS strain may revert to a basic type after mosquito transmission.

Antigenic diversity in Babesia divergens: preliminary results with three monoclonal antibodies to the rat-adapted strain.

Three murine monoclonal antibodies were raised against the rat-adapted strain of Babesia divergens. In the indirect fluorescent antibody test (IFAT) the monoclonals did not react with B microti or B bovis. The monoclonals in IFAT gave high titres with the rat-adapted strain of B divergens, but showed variable reactivity with field isolates of the parasite indicating antigenic diversity in this parasite. Two of the monoclonals, as ascitic fluid, were protective against the rat-adapted strain in splenectomised rats.

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.

Induction of secondary antibody responses to Plasmodium chabaudi in vitro.

Spleen cells and peripheral blood mononuclear cells (PBMC) from mice, which had recovered from infection with Plasmodium chabaudi, were induced to produce anti-P. chabaudi antibody by incubating the cells with P. chabaudi parasitized red cells in Marbrook cultures. The anti-malarial antibody was assayed using the indirect fluorescent antibody test. Spleen cells and PBMC from mice infected 2-4 months previously gave higher antibody titres in culture than similar cells from mice infected a year previously. There was a good correlation between the ability of spleen cells or PBMC to be stimulated to produce antibody in vitro and the ability of mice similar to the cell donors to resist a challenge infection. Some immunity can be adoptively transferred with both spleen cells and PBMC.