Characterization of sporozoite surface antigens by indirect immunofluorescence: detection of stage- and species-specific antimalarial antibodies.

Indirect immunofluorescence (IF) was used to localize stage-specific antigen(s) on the surface of the sporozoite membrane. The authors examined the feasibility of using an IF assay to determine whether an antisporozoite response is developed by individuals living in endemic areas. The specificity and sensitivity of the IF assay were first defined by using hyperimmune sera of sporozoite-immunized hosts protected against rodent (P. berghei), simian (P. knowlesi), and human (P. falciparum, P. vivax) malarias. Species- and stage-specific antisporozoite antibodies were detected by this technique when viable or glutaralde-hyde-fixed sporozoites were used as antigen. The sensitivity of indirect immunofluorescence was found to be 5-10 times greater than that of the circumsporozoite precipitation (CSP) assay. Preliminary studies on sera obtained from individuals living in endemic areas showed that the IF assay can be used to detect species- and stage-specific antisporozoite antibodies in sera of naturally-infected human and simian hosts.