Interactions between Neoparamoeba spp. and Atlantic salmon (Salmo salar L.) immune system components

• Main Author: Gross, Kally Anne
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: Atlantic salmon; Paramoebidae; Bacterial gill disease; Fishes; Salmo salar
• Online Access: https://eprints.utas.edu.au/19844/; https://eprints.utas.edu.au/19844/7/whole_GrossKallyAnne2007_ex_pub_mat_thesis.pdf; https://eprints.utas.edu.au/19844/1/whole_GrossKallyAnne2007_thesis.pdf

The protozoan parasite Neoparamoeba spp. infects the gills of marine cultured Atlantic salmon in Tasmania, Australia causing amoebic gill disease (AGD) and if untreated causes significant production losses. Knowledge of the interaction between Neoparamoeba spp. and host immune factors or cells is limited; specific anti-Neoparamoeba spp. antibodies are present in the serum of fish naturally exposed and sheep anti-Neoparamoeba spp. antibodies do not affect the viability of Neoparamoeba spp. This thesis investigates in vitro and in vivo interactions between the host (Atlantic salmon) and Neoparamoeba spp. The effect of Neoparamoeba spp. on in vitro innate immune cell function was investigated. Sonicated Neoparamoeba spp. did not stimulate a respiratory burst response from anterior kidney leukocytes (P> 0.05). However, there was evidence of priming as cells incubated with the pathogen and then stimulated with phorbol myristate acetate (PMA) produced more (P < 0.05) reactive oxygen species (ROS) than cells stimulated with PMA alone. Neoparamoeba spp. culture supernatant did not affect immune cell function (P> 0.05). Further in vitro investigations found that there was no effect of host serum and mucus on parasite viability (P> 0.05). The effect of Neoparamoeba spp. infection on in vitro gill cell function was assessed. A technique was developed to isolate viable gill cells from perfused gills. Gill cells were tested for their ability to produce ROS, engulf yeast cells and chemotaxis. Cells did not produce ROS in the presence of PMA above basal levels, did not chemotactically migrate and few cells were capable of phagocytosis despite cell viability greater than 80 %. In light of these observations further studies utilised anterior kidney cells. Anterior kidney cells were used to investigate the effect of gill infection on innate immune cell function (ROS production, phagocytosis and chemotactic ability) ex vivo. There was a significant (P <0.05) effect of infection on ROS production 8 and 11 days post Neoparamoeba spp. exposure. A previous study reported increased resistance to AGD in fish that had been infected with Neoparamoeba spp. However, these results were not consistent with the experiences of commercial aquaculture ventures that have performed similar investigations; therefore the study was repeated. It was found that recovered fish were equally susceptible (P> 0.05) to disease upon re-infection as naïve fish. Immunohistochemistry was used to identify Ig bearing cells in the gills of Atlantic salmon. The spatial and temporal distribution of Ig bearing cells was not different between affected and un-affected fish (P> 0.05). Together the data presented in this thesis identify that the interactions between host and pathogen are complex. The parasite may elude destructive immune cell defences by avoiding initiation of deleterious mechanisms or by immunosuppression.