The early stages of the immune response of the European abalone Haliotis tuberculata to a Vibrio harveyi infection

• European abalone hemocyte responses were investigated after a Vibrio harveyi exposure.
• After 3 h, the Rel/NF-κB signal transduction pathway was activated.
• V. harveyi was detected in hemolymph after 9 h, and the concentration increased after 24 h.
• After 9 h, the expression of genes involved in immune response increased.
• After 24 h, the immune response was repressed in both cellular and molecular levels.

Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone mortalities in France, Japan and Australia. In the European abalone, V. harveyi invades the circulatory system in a few hours after exposure and is lethal after 2 days of infection. In this study, we investigated the responses of European abalone immune cells over the first 24 h of infection. Results revealed an initial induction of immune gene expression including Rel/NF-kB, Mpeg and Clathrin. It is rapidly followed by a significant immuno-suppression characterized by reduced cellular hemocyte parameters, immune response gene expressions and enzymatic activities. Interestingly, Ferritin was overexpressed after 24 h of infection suggesting that abalone attempt to counter V. harveyi infection using soluble effectors. Immune function alteration was positively correlated with V. harveyi concentration. This study provides the evidence that V. harveyi has a hemolytic activity and an immuno-suppressive effect in the European abalone.

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