Induction of sporozoite‐specific memory cells in mice immunized with a recombinant Plasmodium vivax circumsporozoite protein

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Abstract
A recombinant Plasmodium vivax circumsporozoite (CS) protein (rPvCS‐1) has been investigated as a possible malaria sporozoite vaccine candidate. Experiments were carried out to determine whether sporozoite‐specific memory cells develop in Swiss Webster mice immunized with rPvCS‐1. Challenge of rPvCS‐1‐immunized mice with P. vivax sporozoites resulted in a 100‐fold increase in the mean serum anti‐sporozoite antibody titer. The presence of parasite‐specific T helper cells was demonstrated using an in vitro assay. Anti‐CS antibodies were detected in the culture supernatants of spleen cells of rPvCS‐1‐immunized mice following in vitro challenge with P. vivax sporozoite extract. Immune spleen cells depleted of T cells did not produce antibodies when challenged with sporozoite extract in vitro. In conclusion, immunization of mice with the rPvCS‐1 protein induced memory T cells which recognized native CS antigen and functioned as T helper cells in the production of anti‐sporozoite antibodies both in vivo and in vitro.