Global 3D imaging of Yersinia ruckeri bacterin uptake in rainbow trout fry.

Maki Ohtani,Martin Kristian Raida,Erling Olaf Koppang,Kasper Rømer Villumsen,Clive M Gray

doi:10.1371/journal.pone.0117263

Maki Ohtani, Martin Kristian Raida + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0117263

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Abstract

Yersinia ruckeri is the causative agent of enteric redmouth disease (ERM) in rainbow trout, and the first commercially available fish vaccine was an immersion vaccine against ERM consisting of Y. ruckeri bacterin. The ERM immersion vaccine has been successfully used in aquaculture farming of salmonids for more than 35 years. The gills and the gastrointestinal (GI) tract are believed to be the portals of antigen uptake during waterborne vaccination against ERM; however, the actual sites of bacterin uptake are only partly understood. In order to obtain insight into bacterin uptake during waterborne vaccination, optical projection tomography (OPT) together with immunohistochemistry (IHC) was applied to visualize bacterin uptake and processing in whole rainbow trout fry. Visualization by OPT revealed that the bacterin was initially taken up via gill lamellae from within 30 seconds post vaccination. Later, bacterin uptake was detected on other mucosal surfaces such as skin and olfactory bulb from 5 to 30 minutes post vaccination. The GI tract was found to be filled with a complex of bacterin and mucus at 3 hours post vaccination and the bacterin remained in the GI tract for at least 24 hours. Large amounts of bacterin were present in the blood, and an accumulation of bacterin was found in filtering lymphoid organs such as spleen and trunk kidney where the bacterin accumulates 24 hours post vaccination as demonstrated by OPT and IHC. These results suggest that bacterin is taken up via the gill epithelium in the earliest phases of the bath exposure and from the GI tract in the later phase. The bacterin then enters the blood circulatory system, after which it is filtered by spleen and trunk kidney, before finally accumulating in lymphoid organs where adaptive immunity against ERM is likely to develop.

Highlights

In fish, even formalin-killed Yersinia ruckeri, known as a “bacterin”, added to the water as an immersion vaccine can induce immunity against enteric redmouth disease (ERM), caused by Y. ruckeri
Yersinia ruckeri Bacterin Uptake in Rainbow Trout commercially available fish vaccine was an ERM vaccine based on a whole cell Y. ruckeri bacterin that can be administered to fish by immersion [3,4,5,6]
No Y. ruckeri bacterin in the form of positive signals was seen in any organs of non-vaccinated negative control fish during the experiment (S1 Fig.)

Summary

Introduction

Even formalin-killed Yersinia ruckeri, known as a “bacterin”, added to the water as an immersion vaccine can induce immunity against enteric redmouth disease (ERM), caused by Y. ruckeri. This bacterium is ideal for studying the fascinating and fundamental mechanism of antigen uptake in the fish from the surrounding water [1,2]. The uptake of Y. ruckeri bacterin induces an increase in transcripts of several pro-inflammatory genes in the spleen of rainbow trout fry and development of adaptive immunity [7]. The Y. ruckeri specific antibodies in rainbow trout are secreted from B lymphocytes and plasma cells in the lymphoid organs such as spleen and kidney [16,17,18]

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