Dinâmica espaço-temporal de eosinófilos em granulomas induzidos pela infecção natural e experimental por Schistosoma mansoni: uma abordagem histopatológica, imunohistoquímica e tridimensional

Abstract

Eosinophils have historically been credited with host protection against helminths such as Schistosoma mansoni – the causal agent of schistosomiasis –, a neglected tropical disease. These cells massively accumulate within granulomas, mainly in the liver, the pathological hallmark of Schistosoma infection. The way in which eosinophils impact the granuloma life remains controversial. A big hurdle in understanding the eosinophil role in schistosomiasis is the complex and dynamic granuloma nature. In this work, eosinophils were mapped across evolutional hepatic granulomas during experimental (Swiss mice) and natural (wild reservoir Nectomys squamipes) S. mansoni infection. Liver fragments from both models were prepared for histopathological analysis of Whole Slide Imaging (WSI). The following parameters of the granulomas were evaluated: (i) identification and distribution; (ii) area; (iii) delimitation of spatial zones; (iv) quantification of eosinophils and other cells; (v) immunostaining for MBP-1. Eosinophils were also qualitatively and quantitatively evaluated by transmission electron microscopy (TEM). A three-dimensional (3D) reconstruction of entire granulomas across all evolutional stages was also performed. Thus, we discovered that granulomas are an evolutionary system with a dynamic nature due to gradual changes in their microarchitecture. In granulomas from both experimental and natural infections, eosinophils are spatially organized and occupy an important peripheral ecological niche conserved throughout space and time. MBP-1 immunostaining in granulomas from the experimental model confirms the preferential spatial localization of eosinophils. Ultrastructural analyses displayed a robust interaction of mature and immature eosinophils with other immune cells in this niche and identified that these cells complete their maturation within granulomas and degranulate by piecemeal. This spatial compartmentalization, not associated with parasite eggs, challenges the concept of eosinophils as a “helminth killer” cell and invigorates their view as an immunoregulatory cell in schistosomiasis. The discovery of the ecological niche of eosinophils within the granuloma periphery contributes to a better understanding of the biological complexity of eosinophil-parasite-microenvironment interaction during helminth infections.