Biodegradable microparticles covalently linked to surface antigens of the scuticociliate parasite P. dicentrarchi promote innate immune responses in vitro

The histiophagous scuticociliate endoparasite Philasterides dicentrarchi is an emerging pathogen that infects the turbot Scophthalmus maximus and thus causes important economic losses in turbot aquaculture. This in vitro study investigated the adjuvant capacity of biodegradable microspheres (MS) composed of two polymers (chitosan and Gantrez®) covalently coupled to surface antigens (Ag) of P. dicentrarchi. The coupled MS–Ag significantly stimulated the phagocytic response of both murine macrophages (RAW 264.7 cells) and leukocytes from the anterior kidney of turbot (HLK), at a level similar to that induced by zymosan A. The MS–Ag also significantly increased production of reactive oxygen and nitrogen species, as shown by the increased O2 consumption and stimulation of the respiratory burst and nitric oxide production by murine and in particular by turbot HLK. The MS–Ag stimulated the production of the proinflammatory cytokine tumour necrosis factor alpha (TNFα) by murine and turbot HLK. The results confirm the high adjuvant capacity of biodegradable MS covalently bound to Ag as regards stimulating the innate immune response, and they justify the use of MS in the production of safe and effective vaccines against fish pathogens.