Eimeria falciformis BayerHaberkorn1970 and novel wild derived isolates from house mice: differences in parasite lifecycle, pathogenicity and host immune reactions

Abstract

Species of Eimeria (Apicomplexa:Coccidia) differ in the timing of lifecycle progression and resulting infections vary in host immune reactions and pathology they induce. Eimeria infections in house mice are used as models for e.g. basic immunology and the most commonly used isolates have been passaged in laboratory mice for over 50 years. We questioned in how far such isolates are are still representative for infections in natural systems. In the current study, we address this question by comparing the ″laboratory isolate″ E. falciformis BayerHaberkorn1970 with a novel, wild derived isolate E. falciformis Brandenburg88, and contrast this with another novel wild derived isolate, E. ferrisi Brandenburg64. We compare parasite lifecycle progression for all three isolates. We relate this to immune cell infiltration at the site of infection (in the caecum) and cytokine gene expression in the spleen as a measure of host immune response. In addition we measure host weight loss as a measure of pathogenicity. A species-specific slower parasite lifecyle progression and higher pathogenicity are observed for E. falciformis vs. E. ferrisi. Host cytokines, in contrast, are expressed at significantly higher level in the spleen of mice infected with the E. falciformis laboratory isolate than in both wild derived isolates, irrespective of the species. Differences in histopathology are observable between all three isolates: The E. falciformis BayerHaberkorn1970 laboratory isolate induces the strongest inflammation and cellular infiltration (with lymphocytes, plasma cells and eosinophilic granulocytes) followed by the wild derived E. falciformis Brandenburg88 isolate. E. ferrisi Brandenburg64 is inducing milder histological changes than both E. falciformis isolates. It can be speculated that the serial passaging of E. falciformis BayerHaberkorn1970 has resulted in evolutionary divergence of this isolate rendering it more virulent in NMRI mice. More generally, our results show that caution is needed when findings from experimental infection with laboratory strains should be integrated with observations in natural systems.