Neutrophil extracellular traps induced by Haemonchus contortus excretory-secretory proteins varies among goats, gerbils, and mice.

BACKGROUND

Previous studies indicated that infection with Haemonchus contortus is host-specific (goat: susceptible host; gerbil: paratenic host; mouse: resistant host). Neutrophils play an essential role in host defense against parasitic infection through phagocytic engulfment, reactive oxygen species (ROS) generation, and neutrophil extracellular traps (NETs) formation. NETs are large web-like complexes consisting of a DNA scaffold decorated with various proteins components, including histones, myeloperoxidase, and elastase. They are released through both ROS-dependent and ROS-independent pathways. Previous studies have demonstrated both constraints and effectiveness of NETs in helminths. However, the roles of NETs in anti-infection of H. contortus in different hosts are still unclear.

METHODS

To assess host-specific variations in NETs release, neutrophils isolated from goats, gerbils, and mice were co-cultured with Haemonchus contortus third-stage larvae (HcL3), followed by quantitative analysis of NETs formation using the PicoGreen® fluorescence assay. Subsequently, H. contortus excretory-secretory proteins (HcESPs) were co-cultured with neutrophils isolated from each host species. NETs release and ROS production were then quantitatively assessed using PicoGreen® fluorescence intensity and oxidation-sensitive dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescence. In addition, the neutrophil's phagocytic ability for FITC-dextran was evaluated by flow cytometric analysis. Finally, to elucidate the signaling pathways involved in HcESP-induced NETs release in goat neutrophils, four specific inhibitors were employed for pretreatment prior to stimulation.

RESULTS

Our results demonstrate that in vitro stimulation with HcL3 triggers NETs formation. The release of NETs exhibits significant host-specific variation, specifically, neutrophils from mice showed the highest NETs release, followed by gerbils, and a minimal response in goats. Moreover, HcESP treatment markedly inhibited ROS generation and phagocytic capacity in neutrophils from all three host species. Intriguingly, HcESPs exerted host-specific modulation of NETs release, with inhibition observed in goats, enhancement in mice, and context-dependent modulation in gerbils. Mechanistic investigations revealed that the NETs suppression in goats neutrophils involved both nicotinamide adenine dinucleotide phosphate (NADPH) oxidase- and neutrophil elastase-dependent pathways.

CONCLUSIONS

Our results demonstrate that HcESPs significantly inhibit NETs formation in goat neutrophils through dual modulation of NADPH oxidase and neutrophil elastase activity. This finding highlights these two enzymes as promising molecular targets for anti-helminthic vaccine development.