Abstract: Objective To investigate immunogenicity and protection efficacy of the recombinant hypoxanthine-guanine-xanthine （HGXPRT） of Plasmodium falciparum expressed in Pichia pastoris. Methods 35 BALB/c mice were divided randomly into five groups: HGXPRT+ISA720 experiment group, HGXPRT+Freund experiment group, ISA720 adjuvant control group, Freund adjuvant control group, and blank control group. BALB/c mice were subcutaneously immunized three times with the HGXPRT protein formulated by either Freund or ISA720 adjuvants at a three weeks interval. Mice were bled via tail vein at 2 weeks after each immunization. Specific antibodies were detected by ELISA as well as IFAT using cultured parasites. The immunized mice were challenged with 10⁵ P.yoelii 10 days after the third immunization and parasitemia was monitored daily by examining Giemsa-stained thin film. Results Strong immune response was induced by the HGXPRT antigen formulated with the adjuvant. Antibody titers of more than 1∶10⁵ were detected after the third immunization while no specific antibody was detected in the mice immunized with adjuvants only. The antibodies against HGXPRT recognized the cultured parasite by IFAT. Four days after mice were challenged with P.yoelii, high parasitemia appeared in the two control groups, which were 24 h earlier than experiment groups. The mean parasitemia of HGXPRT+ISA720 experiment group（29.3%） was significantly lower than that of control groups （70.0%） （P<0.05）. The mean parasitemia of HGXPRT+Freund experiment group （51.0%） was significantly lower than that of adjuvant control （60.7%） and blank control（70.0%） （P<0.05）. Conclusion HGXPRT of P.falciparum expressed in Pichia pastoris was highly immunogenic in mice. Antibody against the recombinant protein recognizes the cultured parasites, and immunization of mice with the recombinant protein provideｓ partial protection against the challenge of P. yoelii.

Key words: Plasmodium falciparum, Pichia pastoris, HGXPRT, Immunogenicity, Plasmodium yoelii