Abstract: AIM:To study the protective immunity of Plasmodium yoelii(P.y) 5 3k Da antigen.
METHODS:BALB/c mice were immunized with3doses of P.y 53k Da protective antigen and then
challenged ip with nonvirulent P.y infected erythrocytes1 0 days after the third im- munization.
Observations on Con A or P.y antigen- induced production of IL - 2 by spleen cells in vitro were
carried out during vaccination period and at days6 ,1 2 ,1 8after challenge. The relationship
between the levels of IL- 2 and parasitaemia was analysed. RESULTS: The IL-2 levels induced by P. y 53 kDa antigen and ConA were much higher in immunized group than in the unimmunized groups before challenge. The peak rate of parasitaemia of the immunized group was 1. 9% , which is much lower than that of 26. 1% in the unimmunized mice and 25. 4% in mice immunized with Freund’s complete adjuvant. CONCLUSION: P. y 53kDa antigen can induce a marked immune protection in mice against erythrocytic stage of P.yoelii.

Key words: Plasmodium yoelii, protective antigen, interleukin- 2, parasitaemia