T-cell tolerance and exhaustion in the clearance of Echinococcus multilocularis: role of inoculum size in a quantitative hepatic experimental model

Chuanshan Zhang,Yingmei Shao,Ning Yang,Renyong Lin,Hui Wang,Cheng Sun,Liang Li,Guodong Lü,Tuerganaili Aji,Zhide Li,Shuting Yang,Xiaojuan Bi,Hao Wen,Dominique A Vuitton

doi:10.1038/s41598-017-11703-1

Abstract

The local immune mechanisms responsible for either self-healing or sustained chronic infection are not clear, in the development of E. multilocularis larvae. Here, we developed a suitable experimental model that mimics naturally infected livers, according to the parasite load. We demonstrated that local cellular immunity and fibrogenesis are actually protective and fully able to limit metacestode growth in the liver of low or medium dose-infected mice (LDG or MDG), or even to clear it, while impairment of cellular immunity is followed by a more rapid and severe course of the disease in high dose-infected mice (HDG). And recruitment and/ or proliferation of memory T cells (including CD4 Tem, CD8 Tcm and CD8 Tem) and imbalance of T1/T2/T17/Treg-type T cells in liver were not only associated with clearance of the parasite infection in LDG, but also with increased hepatic injury in HDG; in particular the dual role of CD8 T cells depending on the parasite load and the various stages of metacestode growth. Besides, we first demonstrate the association between LAG3- or 2B4-expressing T cells exhaustion and HD inocula in late stages. Our quantitative experimental model appears fully appropriate to study immunomodulation as a therapeutic strategy for patients with Alveolar Echinococcosis.

Highlights

The local immune mechanisms responsible for either self-healing or sustained chronic infection are not clear, in the development of E. multilocularis larvae
The common immunological knowledge of experimental E. multilocularis infection comes from studies using experimental mice with intraperitoneal, subcutaneous or intrahepatic infection[18,19,20]
Portal vein injection might be more relevant, in terms of location of secondary E. multilocularis infection, there are very few reports on the portal route to inoculate E. multilocularis metacestode into intermediate hosts[21], and they have not addressed the immunological components of E. multilocularis infection

Summary

Introduction

The local immune mechanisms responsible for either self-healing or sustained chronic infection are not clear, in the development of E. multilocularis larvae. Host-parasite interactions may be studied by using a model of primary infection of intermediate hosts, after ingestion of E. multilocularis eggs[7]; in addition to being at risk for the operator, the route of infection involves numerous host-dependent steps and the outcome is dependent on non-immunological events, such as gastric and enteric enzymes, bile composition, or nature of the intestinal barrier It is the reason why host-parasite immunological relationship has usually been investigated experimentally using secondary AE, in which homogenates of the larval parasite are injected in the peritoneum[8], in the subcutaneous space[9] or directly in the liver[10] of animal intermediate hosts. As protoscoleces (PSCs), which in the parasite cycle transform into adult worms in the definitive hosts, are able to differentiate into metacestode, direct injection of precise numbers of PSCs in the portal vein could overcome the usually encountered difficulties and make us able to characterize the systemic and local, hepatic, immune mechanisms which either clear E. multilocularis larvae from the liver or maintain a chronic infection, and to assess the influence of parasite load on these mechanisms

Methods

Results

Conclusion