Harris L. Rotman

IL‐12 eliminates the Th‐2 dependent protective immune response of mice to larval Strongyloides stercoralis

The goal of the present study was to determine if immune‐mediated killing of S. stercoralis L3 in mice could be modulated by shifting from a Th‐2 to a Th‐1 type immune response. L3 killing in immunized mice was ablated in CD4+ T cell‐depleted animals, but not in CD8+ T cell‐depleted or β2‐microglobulin‐deficient mice. Treatment of immunized mice with IL‐4 or IL‐5 neutralizing MoAb significantly reduced the protective effects of vaccination against S. stercoralis, while protective immunity was unimpaired in IFN‐γ knockout mice. Recombinant IL‐12 was administered to infected mice to switch the immune response from a Th‐2 to a Th‐1 type response. Protective immunity was ablated in immunized mice that received IL‐12 therapy. Eosinophil numbers, eosinophil peroxidase levels, and parasite‐specific IgG1 levels were lowered in IL‐12 treated immunized animals, and parasite‐specific IgG2a levels were increased in these animals. The data indicate that eosinophils are important as mediators of larval killing, and that the establishment of Th‐2 type immunity results in killing of infective S. stercoralis L3, while a shift to Th‐1 type immunity abrogates protective responses.

Strongyloides stercoralis host-adapted third-stage larvae are the target of eosinophil-associated immune-mediated killing in mice.

Host-adapted, transformed, Strongyloides stercoralis third-stage larvae (L3+) were previously found to be antigenically different from free-living, infective, third-stage larvae (L3). These antigenic differences were reproduced by transformation of free-living larvae in tissue culture medium at 37 C over 24 hr. Transformed L3 of both derivations were given as challenge infections in diffusion chambers to naive mice and mice immunized with S. stercoralis L3. Within 12 hr, the challenge infections were killed regardless of whether the L3+ were generated in vitro or in vivo. Eosinophils, previously found to be important in the immune response to S. stercoralis larvae, were recruited into the L3+ microenvironment within 12 hr of challenge infection in immune mice, which supports the previously proposed mechanisms of S. stercoralis larval killing. Thus, S. stercoralis L3+ appear to be targets of the immune response in mice instead of being involved in immune evasion.

Immunity to a challenge infection of Strongyloides stercoralis third-stage larvae in the jird

Jirds support the entire life‐cycle of Strongyloides stercoralis. We therefore used this host as a model to define the mechanism of the immune response to a challenge infection, as well as the parasite stage effected by the response. Jirds given a primary infection of S. stercoralis are resistant to re‐infection. The use of implanted diffusion chambers containing larvae showed that the immune response killed the third‐stage larvae, and this was confirmed by subcutaneous infections. The larvae of a challenge infection are killed within 48 h, a time period too short to allow for the development of L4 and adult worms. The immune response is dependent on both a serum factor and cells, suggestive of an ADCC type response.

Strongyloides stercoralis: high worm population density leads to autoinfection in the jird (Meriones unguiculatus)

At 28 days post-infection autoinfective third-stage larvae (L3a) of Strongyloides stercoralis occurred in jirds infected with 10,000 infective third-stage (L3i). Previously in the jird model of strongyloidiasis, autoinfection had been seen in immunologically immature or immunosuppressed jirds only. The heavily infected jirds described herein had a strong anti-L3i immune response at the same time the living L3a were found in their tissues. This was demonstrated by the rapid killing of L3i in subcutaneously implanted diffusion chambers. No decrease of intestinal motility was observed in these heavily infected jirds, indicating that an increased time for development was not the explanation for the presence of L3a. These larvae were found only in jirds when concomitantly a large number of first-stage larvae (L1) occurred in the intestines. We suggest that the development of L3a in the adult jird model is a rare event and thus, autoinfection occurs only when the intestinal population of L1 is very large, as was the case in the heavily infected jirds. Index Descriptors and Abbreviations. Nematode; Strongyloides stercoralis; Mongolian gerbil; Meriones unguiculatus; autoinfection; larval development; L3i, infective third-stage larva(e); L3i+, tissue migrating third-stage larva(e); L3a, autoinfective third-stage larva(e); L1, first-stage larva(e); PI, post-infection.

Structural and molecular specificity of antibody responses in mice immune to third stage larvae of Onchocerca volvulus.

Immunization of mice with irradiated Onchocerca volvulus infective stage larvae (L3) has been demonstrated to confer protection against challenge infections with these larvae. Additionally, cytokine level measurements and cytokine depletion studies have shown that both IL‐4 and IL‐5 are important in generating a protective immune response against O. volvulus challenge infections, thus suggesting a dependency of protective immunity on IgG1, IgE and/or eosinophils. In the present study, we examined the humoral responses of immunized mice to O. volvulus L3 antigens. ELISA measurements of total serum antibody levels indicated that IgE was the only antibody isotype elevated in mice immunized with O. volvulus L3. IgM from immunized mice was the only isotype that recognized surface antigens on intact O. volvulus L3. IgG1, IgG3, IgE and IgA recognized internal parasite antigens on O. volvulus L3 frozen sections. Western blot analysis of L3 proteins showed that in serum from mice immunized with O. volvulus L3 IgG1, IgG2a/2b, IgA, and IgE, as well as IgM, recognized unique L3 proteins. Antibodies in serum from L3 immunized mice were able to detect O. volvulus adult antigens in a pattern similar to the recognition found in O. volvulus L3. Some L3 antigens were shared by adults, while other antigens were L3 specific. The ELISA, immunohistochemistry and Western blot findings thus demonstrate a complex pattern of antigen recognition of parasite antigens by antibodies found in mice immune to the L3 of O. volvulus