The innate immune system is the first line of host defense against invading pathogens across the entire animal kingdom. Pathogen recognition and effective response are essential to survive in a microbe-rich environment that often characterizes certain types of tilapia aquaculture. In this thesis, we developed a platform to study the innate immune response of the Nile tilapia (Oreochromis niloticus). Specifically, a macrophage model system was characterised and used to explore PAMP-PRR interactions. Moreover, the basal expression of targeted innate immunity gene was measured in different tissues of tilpia, cultured under different aquaculture environments.
The macrophage primary cell culture was used to characterize PAMP-PRR interactions after stimulation with upPGN or dsRNA at the level of mRNA transcription of cytokines and antiviral related genes using absolute qPCR and secreted prostaglandins in the cell supernatant. A phylogenetic study of the target genes revealed conservation of Nile tilapia innate immunity genes across different species and all extant teleosts. Head kidney derived macrophages from Nile tilapia were optimally cultured and stimulated with PAMPs over specific time periods. Results revealed moderate levels of secreted PGE2 in culture media but no change upon PGN stimulation. Cytokine mRNAs were generally upregulated although high levels of mRNAs were found in basal state cells. Granulomas were observed during cell culture suggestive of chronic infection with intracellular parasites. Mycobacterium detection using PCR based method was able to detect mycobacterium DNA in macrophages and tissues samples of Nile tilapia (Oreochromis niloticus).
The qPCR tools developed were used to examine the tissue-specific gene expression in tilapia cultured in Thailand. Data suggests that red hybrid tilapia (O.niloticus X O. mossambicus) are potentially more sensitive to culture conditions, particularly in polyculture husbandry systems in comparison to Nile tilapia (Oreochromis niloticus).