Early host-parasite interaction models reveal a key role for fibrinolysis in Fasciola hepatica intestinal migration.

Background: Fasciola hepatica is the most common etiologic agent of fasciolosis, a parasitic disease that affects millions of ruminants worldwide and a zoonotic human infection of public health concern. Upon ingestion of infective metacercariae, F. hepatica newly excysted juveniles (FhNEJ) emerge in the duodenum and cross the intestinal wall to initiate a migration route that culminates with their establishment within the hepatic bile ducts. The ability of FhNEJ to exploit the broad-spectrum activities of host plasmin, the central protease of the fibrinolytic system, has been proposed as a strategy employed by these parasites to migrate across the intestinal wall while minimising energy expenditure.

Methods: Mouse intestinal epithelial cells (mPSIEC) were stimulated with FhNEJ and plasminogen (PLG), the zymogen of plasmin, to understand whether FhNEJ-stimulated plasmin generation modulates processes relevant to parasite migration through the intestinal wall, including extracellular matrix (ECM) degradation and the secretion of ECM-degrading enzymes. Plasmin-mediated cellular responses were further examined by proteomic analysis of mPSIEC whole-cell lysates. In parallel, the contribution of the fibrinolytic system in FhNEJ migration was studied in vivo by infecting mice with F. hepatica metacercariae following pharmacological inhibition of fibrinolysis.

Results: Co-stimulation of mPSIEC with FhNEJ and PLG led to increased plasmin generation in the intestinal pericellular space, which was associated with enhanced collagen degradation and secretion of the urokinase-type plasminogen activator. In addition, using independent cell culture replicates and a stringent statistical pipeline, we identified a robust set of differentially expressed proteins in mPSIEC following stimulation with FhNEJ and PLG. These proteins were involved in cell adhesion, migration, ECM remodelling, immune evasion and fibrinolysis. Despite inter-experimental variability, FhNEJ migration in mice was reduced upon pharmacological inhibition of fibrinolysis, supporting the contribution of host fibrinolysis to parasite invasion in vivo.

Conclusions: Altogether, this work provides unprecedented insights into the role of the host fibrinolytic system to FhNEJ migration across mammalian host tissues, thereby advancing our understanding of host-parasite relationships during early stage fasciolosis and highlighting interesting directions for future research in this area.