Intranasal immunization with yeast-expressed 19 kD carboxyl-terminal fragment of Plasmodium yoelii merozoite surface protein-1 (yMSP1₁₉) induces protective immunity to blood stage malaria infection in mice

Variable protection against malaria blood-stage infection has been demonstrated in mice following parenteral immunization with the highly conserved 19 kD carboxylterminal fragment of the merozoite surface protein-1 (MSP₁₉) using CFA/IFA and other adjuvants. Here we show that intranasal immunization of BALB/C mice with yeast expressed Plasmodium yoelii MSP1₁₉ plus a mixture of native and recombinant cholera toxin B subunit, could induce serum MSP1₁₉-specific antibodies at titres ranging from 20,000 to 2.56,000. The Ig subclass responses were predominantly G1 and G2b. Intranasal immunization led to protection following challenge (peak parasitaemia <1%) in mice with the highest MSP₁₉-specific titre (≤640,000). In two of the three protected mice, a peak parasitaemia of 0.1%-1% was followed by a boost of the antibody response whereas one of the three protected mice did not boost its antibody response after a peak parasitaemia of 0.02%. In unprotected mice, antibody levels rose, then fell, following the detection of parasites in the peripheral blood. CD4⁺ T cell-depletion abrogated the ability of the mice to boost their antibody response following challenge. These data demonstrate the potential for intranasal immunization with MSP1₁₉ to protect against malaria.