Acute Plasmodium knowlesi Infection in Olive Baboons (Papio anubis) Is Accompanied by High-Level of Gamma Interferon

Malaria is a major and growing threat to economic development and public health in developing countries. There are about 2.7 million malaria deaths annually. Plasmodium knowlesi, the fifth human malaria parasite, is an attractive model for malaria research and is also phylogenetically close to human malaria parasite P. vivax. It shares many vaccine candidate molecules with P. vivax. This study was carried out to determine immunological profiles mounted by Olive baboons during experimental infection with P. knowlesi H strain. Six Olive baboons (Papio Anubis) were infected with 1×106 P. knowlesi blood stage parasites. The infected baboons developed either severe (acute) or mild (chronic) infection. High IgM titres were observed during primary infection in the baboons. Anti-IgG antibodies were raised after two weeks of chronic infection. Circulating IFNg from serum rose fifty fold in acutely infected animals during the first two weeks post infection compared to a tenfold increase in chronically infected baboons. Recall proliferative responses were two fold higher in chronically infected animals by day 14 post infection. The highest stimulation index (10.06 + 2.74) was observed in chronic animals at day 42 post infection. These results demonstrated that baboons infected with P. knowlesi mount an immune response that is characterized by antibody and cytokine responses involving IgG, IgM and IFNr. These studies are important in validation of the P. knowlesi- baboon model for malaria drug and vaccine development.