Limited effect of adaptive immune response to control encephalitozoonosis

Summary This study revises our understanding of the effectiveness of cell‐mediated adaptive immunity and treatment against microsporidia using molecular detection and quantification of microsporidia in immunocompetent C57Bl/6 and immunodeficient CD 4 −/− and CD 8 −/− mice for the first time. We demonstrate an intense dissemination of microsporidia into most organs within the first weeks post‐infection in all strains of mice, followed by a chronic infection characterized by microsporidia persistence in CD 4 −/− and C57Bl/6 mice and a lethal outcome for CD 8 −/− mice. Albendazole application reduces microsporidia burden in C57Bl/6 and CD 4 −/− mice, whereas CD 8 −/− mice experience only a temporary effect of the treatment. Surprisingly, treated CD 8 −/− mice survived the entire experimental duration despite enormous microsporidia burden. On the basis of our results, we conclude that microsporidia survive despite the presence of immune mechanisms and treatments that are currently considered to be effective and therefore that CD 8 T lymphocytes represent a major, but not sole effector mechanism controlling microsporidiosis. Furthermore, the survival of mice does not correspond to spore burden, which provides new insight into latent microsporidiosis from an epidemiological point of view.