Haemocyte-derived innate immune reactions of the giant African snail (Lissachatina fulica) against the lungworm Angiostrongylus vasorum

The metastrongyloid parasite Angiostrongylus vasorum is currently considered an emerging gastropod-borne lungworm species of canids and has gained growing scientific attention in recent years. Nonetheless, knowledge of gastropod innate immune reactions and how A. vasorum larvae are attacked by gastropod-derived haemocytes is still very sparse. The current study aims to investigate gastropod haemocyte innate immune reactions in response to A. vasorum L1 larvae and antigen (AvAg) in vitro. Gastropod haemocytes were isolated from the giant African snail (Lissachatina fulica) via cardiac puncture, confronted with AvAg or A. vasorum L1, and thereafter assessed for cell activation status, ROS production and extrusion of invertebrate extracellular phagocyte traps (InEPT). Haemocyte–parasite interactions were assessed via flow cytometry, live cell 3D-holotomographic microscopy as well as scanning electron microscopy (SEM). Overall AvAg stimulation activated haemocytes and induced a time-dependent increase in haemocyte ROS production. Moreover, SEM analyses illustrated the formation of ‘InEPT-like’ structures in response to A. vasorum L1. These novel findings on neglected invertebrate innate immune responses will help to better understand the complex mollusc–metastrongyloid parasite interactions, which contribute to the epizootiology of not only canine angiostrongylosis but also of closely related metastrongyloid nematodes of public and veterinary health concern.