# A major ecological niche of eosinophils in evolving Schistosoma granulomas challenges the eosinophil view as “helminth killer” cells

## TL;DR

Eosinophils in schistosomiasis granulomas are organized in a peripheral niche and act as immunoregulatory cells, not just 'helminth killer' cells.

## Contribution

Reveals a conserved spatial niche of eosinophils in Schistosoma granulomas, challenging their traditional role as helminth killers.

## Key findings

- Eosinophils occupy a major peripheral niche in all granuloma stages.
- Eosinophils interact with immune cells and secrete via piecemeal degranulation.
- The niche is unrelated to parasite eggs and is conserved in both mouse and natural infections.

## Abstract

Eosinophil-rich granulomas, formed around tissue-trapped parasite eggs, are hallmarks of schistosomiasis mansoni, a prevalent neglected tropical disease. How eosinophils populate and affect the complex Schistosoma granulomas remains unclear. Here, we mapped eosinophils across evolutional hepatic granulomas in a mouse model and in a primary wild reservoir for human schistosomiasis in Brazil (water rat Nectomys squamipes). With in-depth quantitative image analysis and three-dimensional histological reconstructions of entire granulomas, we find that eosinophils are spatially organized and occupy a major, peripheral niche conserved across space and time in all granuloma stages and both experimental and natural infections. Within this niche, immature and mature eosinophils coinhabit, compartmentalize their major basic protein-1 content, robustly interact with other immune cells, and secrete through piecemeal degranulation. This unveiled niche, unrelated to parasite eggs, challenges the concept of eosinophil as a “helminth killer” cell and invigorates its view as an immunoregulatory cell of the tissue microenvironment in Schistosoma granulomas.

Discoveries shift understanding of eosinophils in schistosomiasis mansoni.