Abstract
A specific agglutination of Plasmodium knowlesi detectable both by macroscopic and by microscopic methods is described. Agglutinins for Plasmodium knowlesi appear in the sera of monkeys between 15 and 45 days after the onset of the infection and become progressively stronger as the malarial infection gradually subsides. Agglutinins persist in the sera of chronically infected animals for a year or longer. The sera of animals which have been repeatedly superinfected agglutinate parasites at dilutions as high as 1:1,000. Sera from normal monkeys, from monkeys acutely ill with malaria, and from monkeys chronically infected with a different species of malarial parasite (Plasmodium inui) do not agglutinate Plasmodium knowlesi. Immune serum agglutinates mature intracellular or extracellular parasites but does not agglutinate unparasitized cells or cells containing immature parasites. The relation of these observations to the mechanism of active and passive immunity in monkey malaria is discussed.
Highlights
The demonstration of passive immunity in experimental monkey malaria by Coggeshall and Kumm [1, 2] indicates that immune substances are present in the sera of animals with chronic malarial infections and of animals that have been hyperimmunized by superinfection
Leishmania and trypanosomes are agglutinated by normal sera in dilutions lower than the dilutions of immune sera required for agglutination
In order to determine whether a chronic infection with another species of malarial parasite causes the production of agglutinins for P. knowlesi, sera from monkeys with chronic infections with P. inui were tested against the P. knowlesi antigen
Summary
The existence of precipitins and complementfixing antibodies in human malaria has been reported, but up to the present time the specific sensitization and agglutination of malarial parasites by immune serum has not been demonstrated. Brown [11] has reported that the reduction in the charge on the red cells is related to the degree of resistance to the infection This implies a non-specific sensitization of all the red cells, but no agglutination was observed. Malamos [12] observed in the blood of a monkey infected with P. knowlesi and treated with atebrin an agglomeration of red cells which affected, during the early stages of the disease, only the parasitized cells. Sera from five monkeys having chronic infections with P. inui of various durations were tested for agglutination of P. knowlesi
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