Modulation of immune responses by Fasciola hepatica-derived products

Abstract

Helminths are successful pathogens that infect 25% of the world s population. They cause chronic infections that are associated with type-2 and regulatory immune responses that suppress host anti-parasite immune responses. However, helminths can also inhibit immune responses that mediate inflammatory pathology in autoimmune diseases. Indeed, a high prevalence of helminth infections in certain regions has been associated with low incidences of autoimmune diseases. Consequently, helminths are being trialed as potential therapies for immune-mediated diseases. However, the regulatory and practical concerns around their use has led to a search for specific helminth-derived immunoregulatory molecules. Our laboratory has demonstrated that the helminth Fasciola hepatica excretory-secretory products (FHES) can attenuate the development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Protection was mediated by eosinophils and the type-2 cytokines IL-33 and IL-5. FHES is heterogeneous preparation but provides the basis for identifying individual immunomodulatory molecules. In this project, small extracellular vesicles (exosomes) were isolated from FHES by sequential centrifugation and examined for immunomodulatory activity. FH exosomes induced IL-1RA production by macrophages and eosinophils and when injected intraperitoneally into mice promoted recruitment or expansion of eosinophils and alternatively activated macrophages, and suppressed infiltration of pro-inflammatory cells into the peritoneal cavity. Treatment with two single injections of FH exosomes induced anti-inflammatory trained immunity, which rendered the mice less susceptible to the induction of EAE. This was associated with a reduction in the infiltration of pathogenic Th1 and Th17 into the CNS. In order to distinguish individual immunomodulatory proteins, F. hepatica Kunitz Type Molecule (FHKTM), identified in a mass spectrometry screen and was cloned, transformed into yeast, expressed, and purified. FHKTM promoted production of the anti-inflammatory cytokines IL-1RA and IL-10 and the alternative activation of macrophages in vitro. Finally, functional studies demonstrated that FHKTM had regulatory activity in vivo, attenuating the clinical severity of EAE. The findings demonstrate that F. hepatica exosomes and FHKTM promote regulatory immune responses and may be useful in the design of new approaches for the treatment of human inflammatory diseases.