Strongyloides stercoralis: protective immunity to third-stage larvae inBALB/cByJ mice

A murine model system was developed to study the induction and mechanism of protective immunity to L3 of Strongyloides stercoralis. L3 were implanted in BALB/cByJ mice in diffusion chambers constructed with 0.1- or 2.0-microns-pore-size membranes. Parasites survived equally well regardless or membrane type for 7 days, after which larval survival decreased in diffusion chambers constructed with 2.0-microns-pore-size membranes, which allowed host cells to enter. Survival of S. stercoralis L3 in diffusion chambers implanted in mice was assayed after immunization with live, heat-killed, and homogenized L3. Optimal immunization was achieved with 10,000 live L3, whereby immunized mice eliminated 97% of the larvae either contained within diffusion chambers or free within the tissues of the mouse by 24 hr postinfection. Sera from immunized mice had elevated levels of IgG1, IgM, and IgA parasitic-specific antibody; IgM was the only antibody isotype that recognized surface antigens of L3. Larvae were not killed in immunized mice if contact between host cells and the parasites was prevented. In the peripheral blood and diffusion chamber fluid of immunized mice, eosinophil levels were significantly higher when compared to the levels found in control mice. The rodent model developed in the present study has thus demonstrated that virtually complete immunity can be induced to the L3 of S. stercoralis and that larval killing was found to be associated with the presence of both specific antibody and eosinophils.