Host Proteins in E. multilocularis Metacestodes

Metacestodes of the cestode Echinococcus multilocularis are the causative agents of alveolar echinococcosis, a rare and 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 labelled proteins suggest that this uptake may occur independently of protein size or charge. Closer investigation using proteomics draw, however, a different picture. Of 1,170 host (i.e. rat or bovine) proteins 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 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.