Kinetics of the humoral immune response to blood-induced falciparum malaria in the squirrel monkey Saimiri sciureus.

Twenty squirrel monkeys were inoculated with the Palo Alto (FUP) strain of Plasmodium falciparum and treated with quinine one or two weeks after inoculation. Antibody production, measured by the IFA technique, closely followed the appearance of parasites in the blood, rose to a maximum in about two to three weeks, stayed at this level for one to two months and then declined progressively. IgM antibodies appeared faster than any other class of antibody and at two weeks of infection represented 50-80% of total malarial antibodies. IgM antibodies also declined more rapidly and reached barely detectable levels within two to three months. IgG antibodies rose slowly to a maximal level which was, however, maintained for a longer period. No significant differences were observed between intact and splenectomized monkeys. Challenge with virulent parasites two months after the initial infection showed that both groups of monkeys, particularly the intact ones, had acquired a strong protective immunity. The secondary IgG response was stronger when the challenge was performed more than two months after the primo-inoculation.