マウスモデルによるマラリア生ワクチンの研究

抄録

Extensive studies on malaria vaccine have been made to provide new technology for the control of the disease, which is still prevalent in the tropics. Genetic engineering to produce antigen epitope on malaria parasites raised new possibilities in this field, however, a vaccination model of long lasting effect still remains to be investigated. The present study was undertaken to propose a new malaria vaccine model using a rodent malaria system. An established strain, Plasmodium (P) berghei NK65XAT (XAT), is a permanent attenuated derivative of P. berghei NK65 (NK65). Only one parasite of the original NK65 inevitably kills one mouse, while, 10⁷ XAT strain parasites caused a self-resolving type of low parasitemia in mice, and the mice remained apparently healthy. The mice inoculated with 10⁶ XAT parasites showed a potent long-lasting resistance against challenge inoculation with 10⁵ NK65 parasites of high virulence. Complete protection was shown by day 120 after immunization inoculation with XAT. Survival rates of 20-40% were recorded from day 180 to day 360 following the vaccination. The immunized mice were also completely resistant to challenge by a different strains of P. berghei ANKA. Immunity was also effective against challenge by different species of rodent Plasmodia, although 100% protection was not attained. Radical chemotherapy on mice inoculated with XAT did not reduce the immune effect. Hence, the resistance conferred on the immune mice was a different type of immunity from the classic premunition. It has been widely known that malaria causes some type of immune suppression in the host. However, so far as responsiveness of spleen cells to Con A, PHA, LPS and the parasite antigen concerned, suppression was not observed in mice immunized by XAT inoculation. These findings support the view that attenuated live type malaria vaccine could provide potent, long-lasting immunity without endangering the host.