Immersion Vaccination by a Biomimetic-Mucoadhesive Nanovaccine Induces Humoral Immune Response of Red Tilapia (Oreochromis sp.) against Flavobacterium columnare Challenge.

Sirikorn Kitiyodom,Nopadon Pirarat,Teerapong Yata,Kim D Thompson,Channarong Rodkhum,Takayuki Katagiri,Sasithon Temisak,Preetham Elumalai,Katawut Namdee,Janina Costa

doi:10.3390/vaccines9111253

Abstract

Immersion vaccination with a biomimetic mucoadhesive nanovaccine has been shown to induce a strong mucosal immune response against columnaris disease, a serious bacterial disease in farmed red tilapia caused by Flavobacterium columnare. However, the induction of a systemic immune response by the vaccine is yet to be investigated. Here, we examine if a specific humoral immune response is stimulated in tilapia by a biomimetic-mucoadhesive nanovaccine against Flavobacterium columnare using an indirect-enzyme-linked immunosorbent assay (ELISA), serum bactericidal activity (SBA) and the expression of immune-related genes within the head-kidney and spleen, together with assessing the relative percent survival of vaccinated fish after experimentally infecting them with F. columnare. The anti-IgM antibody titer of fish at 14 and 21 days post-vaccination was significantly higher in chitosan complex nanoemulsion (CS-NE) vaccinated fish compared to fish vaccinated with the formalin-killed vaccine or control fish, supporting the serum bactericidal activity results at these time points. The cumulative mortality of the unvaccinated control fish was 87% after challenging fish with the pathogen, while the cumulative mortality of the CS-NE vaccinated group was 24%, which was significantly lower than the formalin-killed vaccinated and control fish. There was a significant upregulation of IgM, IgT, TNF α, and IL1-β genes in the spleen and kidney of vaccinated fish. Significant upregulation of IgM and IgT genes was observed in the spleen of CS-NE vaccinated fish. The study confirmed the charged-chitosan-based mucoadhesive nanovaccine to be an effective platform for immersion vaccination of tilapia, with fish generating a humoral systemic immune response against columnaris disease in vaccinated fish.

Highlights

Flavobacterium columnare, a gram-negative, filamentous, thin rod bacterium, with or without yellow rhizoid colony formation, is a serious pathogenic bacterium causing columnaris disease in intensively farmed tilapias worldwide [1,2]
Only low or partial protection has been reported for columnaris vaccines administered by injection or immersion using formalin-killed whole cell preparations in coho salmon Oncorhynchus kisutch [6], channel catfish Ictalurus punctatus [7,8], eels [9], carp Cyprinus carpio [10], and tilapia Oreochromis niloticus [11,12]
The aim of the present study was to investigate the specific humoral immune response stimulated in tilapia by the biomimetic-mucoadhesive nanovaccine against F. columnare, using an indirect-enzyme linked immunosorbent assay (ELISA) to measure serum antibody responses, serum bactericidal activity (SBA), and the expression of immune-related genes within the head-kidney and spleen

Summary

Introduction

Flavobacterium columnare, a gram-negative, filamentous, thin rod bacterium, with or without yellow rhizoid colony formation, is a serious pathogenic bacterium causing columnaris disease in intensively farmed tilapias worldwide [1,2]. Among the vaccination delivery routes used to administer vaccines to fish, immersion vaccination is considered to be the most suitable for delivering columnaris vaccines to the mucosal tissues to confer a protective mucosal immune response to protect fish against the disease. This approach has been impeded by the fact that the effectiveness of antigen absorption by mucosal tissues is limited and the potency of induction of protective immune responses can be low and short in duration. Our previous study demonstrated the use of a biomimetic-mucoadhesive nanovaccine that allows better adsorption of antigens to the mucosal surfaces of fish [13,14]

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