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Abstract Background Mice are susceptible to infections with the rodent filarial nematode Litomosoides sigmodontis and develop immune responses that resemble those of human filarial infections. Thus, the L. sigmodontis model is used to study filarial immunomodulation, protective immune responses against filariae and to screen drug candidates for human filarial diseases. While previous studies showed that type 2 immune responses are protective against L. sigmodontis, the present study directly compared the impact of eosinophils, IL-5, and the IL-4R on the outcome of L. sigmodontis infection. Methods Susceptible wildtype (WT) BALB/c mice, BALB/c mice lacking eosinophils (dblGATA mice), IL-5−/− mice, IL-4R−/− mice and IL-4R−/−/IL-5−/− mice were infected with L. sigmodontis. Analyses were performed during the peak of microfilaremia in WT animals (71 dpi) as well as after IL-4R−/−/IL-5−/− mice showed a decline in microfilaremia (119 dpi) and included adult worm counts, peripheral blood microfilariae levels, cytokine production from thoracic cavity lavage, the site of adult worm residence, and quantification of major immune cell types within the thoracic cavity and spleen. Results Our study reveals that thoracic cavity eosinophil numbers correlated negatively with the adult worm burden, whereas correlations of alternatively activated macrophage (AAM) numbers with the adult worm burden (positive correlation) were likely attributed to the accompanied changes in eosinophil numbers. IL-4R−/−/IL-5−/− mice exhibited an enhanced embryogenesis achieving the highest microfilaremia with all animals becoming microfilariae positive and had an increased adult worm burden combined with a prolonged adult worm survival. Conclusions These data indicate that mice deficient for IL-4R−/−/IL-5−/− have the highest susceptibility for L. sigmodontis infection, which resulted in an earlier onset of microfilaremia, development of microfilaremia in all animals with highest microfilariae loads, and an extended adult worm survival.

Abstract Background One of the most advantageous research aspects of the murine model of filariasis, Litomosoides sigmodontis, is the availability of mouse strains with varying susceptibility to the nematode infection. In C57BL/6 mice, L. sigmodontis worms are largely eliminated in this strain by day 40 post-infection and never produce their offspring, microfilariae (Mf). This provides a unique opportunity to decipher potential immune pathways that are required by filariae to achieve a successful infection. In this study we tracked worm development and patency, the production of microfilariae and thus the transmission life-stage, in Rag2IL-2Rγ−/− mice which are deficient in T, B and NK cell populations. Findings Although worm burden was comparable between wildtype (WT) and Rag2IL-2Rγ−/− mice on d30, by day 72 post-infection, parasites in Rag2IL-2Rγ−/− mice were still in abundance, freely motile and all mice presented high quantities of Mf both at the site of infection, the thoracic cavity (TC), and in peripheral blood. Levels of cytokine (IL-4, IL-6, TNFα) and chemokine (MIP-2, RANTES, Eotaxin) parameters were generally low in the TC of infected Rag2IL-2Rγ−/−mice at both time-points. The frequency of neutrophils however was higher in Rag2IL-2Rγ−/−mice whereas eosinophils and macrophage populations, including alternatively activated macrophages, were elevated in WT controls. Conclusion Our data highlight that adaptive immune responses prevent the development of patent L. sigmodontis infections in semi-susceptible C57BL/6 mice and suggest that induction of such responses may offer a strategy to prevent transmission of human filariasis.