# Host Proteins in Echinococcus multilocularis Metacestodes

## TL;DR

This study investigates how Echinococcus multilocularis metacestodes take up host proteins, revealing differences in protein uptake under various conditions.

## Contribution

The study identifies specific patterns of host protein uptake by metacestodes and highlights variability depending on the source of the host proteins.

## Key findings

- Only 225 out of 1170 host proteins in the culture medium are found in metacestode vesicle tissue or fluid.
- Alpha-2-HS-glycoprotein is the most abundant protein in vesicle fluid, unlike serum albumin in the culture medium.
- Histone isoforms dominate in vesicle fluid from experimentally infected mice, indicating context-dependent uptake.

## Abstract

Metacestodes of Echinococcus multilocularis are the causative agents of alveolar echinococcosis, a neglected, life-threatening, zoonotic disease. To study these metacestodes in vitro, a model system using a culture medium conditioned by rat hepatoma cells is available. A key question is how the parasite interacts with the host and, in particular, which host-derived compounds are taken up. In this study, we focus on the uptake of host-derived proteins. Studies with artificially labeled proteins suggest that this uptake may occur independently of protein size or charge. Closer investigation using proteomics draws, however, a different picture. Of 1170 host (i.e., rat or bovine) proteins as identified by LC-MS/MS-based proteomics present in the culture medium, only 225 are found in metacestode vesicle tissue or fluid. Moreover, their relative abundances differ. Serum albumin, the most abundant culture medium host protein, is only the third most abundant protein in vesicle fluid, where Alpha-2-HS-glycoprotein becomes the most abundant protein. In vesicle fluid obtained ex vivo from experimentally infected mice, the situation is again different, with histone isoforms as the most abundant proteins. This suggests that while maintaining their internal milieu constant, metacestodes may adjust the spectrum of host proteins taken up. Potential uptake mechanisms and functions are discussed.