# The critical window for host defense: macrophage trogocytosis eliminates Echinococcus multilocularis at the early establishment stage

## TL;DR

Macrophages eliminate Echinococcus multilocularis early in infection through a process called trogocytosis, which is critical for host defense.

## Contribution

This study identifies macrophage trogocytosis as a novel mechanism for early elimination of Echinococcus multilocularis.

## Key findings

- Macrophage infiltration and parasite clearance in the liver occur within 24 hours post-infection.
- Trogocytosis, requiring active serum components, is the primary mode of protoscolex elimination by macrophages.
- Two lesion phenotypes were identified: progressive and regressive, based on macrophage activity and parasite fate.

## Abstract

The ability of Echinococcus multilocularis (E.m) to establish infection depends on evading host immune clearance during the early stages. This study investigated the mechanisms by which host macrophages eliminate E.m during this critical window.

We utilized a mouse infection model with fluorescently labeled protoscoleces to observe early immune dynamics in vivo. Histopathological analysis was performed to characterize lesion phenotypes. The mechanism of parasite killing was further explored using in vitro co-culture experiments and scanning electron microscopy (SEM).

Rapid immune cell infiltration and parasite clearance in the liver were observed within 24 hours post-infection. Histopathological analysis revealed two distinct lesion phenotypes: "Progressive Lesions," characterized by a failure of macrophage infiltration and parasite transformation into vesicles, and "Regressive Lesions," marked by high macrophage density and complete parasite elimination. In vitro experiments demonstrated that macrophages mediated protoscolex killing through complement-dependent trogocytosis, a process requiring active serum components. SEM confirmed direct macrophage-parasite contact and trogocytosis as the primary mode of elimination.

These findings highlight the pivotal role of macrophage trogocytosis in early host defense against E.m infection and provide new insights into the mechanisms of innate immunity in parasitic clearance.