الفهرس 
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Abstract
Nile tilapia (Oreochromis niloticus) also named as “Food fish of the 21st century” is robust fish that can dwell well even in hostile aquatic envi¬ronments. High adaptability, rapid growth, and high yield make tilapia a valuable species for the commercial culture. In recent times, tilapia cultures have been impacted by bacterial pathogens including Aeromonas hydrophila which is common occurrences, has caused enormous economic losses due to high mortality with decreasing the fish weight and sale with decreasing of fish farm returns. So, this study was conducted to understand the expression of IL-1β and IFN-γ genes during infection with A. hydrophila in Nile tilapia.
This study has been performed on apparently healthy Nile tilapia purchased from a private fish farm at Assiut Governorate. Fish were transported to our lab. Fish were kept in 1500 L flow-through tanks and acclimated to the Lab conditions for two weeks. Fish has been infected with a pathogenic strain of A. hydrophila that was previously isolated in our lab from O. niloticus. Fish was exposed, by immersion, to A. hydrophila culture (7.2×105 CFU/ml) for 1 h. Clinical signs and mortalities of the challenged fish were recorded daily for 14 days. Nine Nile tilapia (3x3) were randomly selected from different aquaria of the treated and control groups in each time point (1st, 2nd, 3rd, 5th, 7th, 10th, & 14th day post-infection; DPI). Fish were euthanized to collect samples (gills, intestine, liver, spleen, and kidney). The samples were preserved in RNAlater and stored at −80°C until RNA extraction. In this study, RNA extraction and quantification for collected samples have performed then RNA was used for the generation of the first-strand cDNA to perform quantitative real-time PCR (RT-qPCR). The target genes (IL-1β and IFN-γ genes) were normalized to both beta-actin and EF-1α genes (housekeeping genes or calibrator).
Expression of IL-1β and IFN-γ were increased in several tissues. In brief, IL-1β was expressed in several tissues, such as gills, spleen, kidney, intestine, liver, with the highest gene expression have been detected in the gills (10.2-fold) followed by intestine, liver, and kidney to give 7.8-, 5.5-, and 5.3-fold, respectively. However, the lowest IL-1β expression level has been detected in the spleen (5.2-fold). The highest expression of IFN-γ has been detected in both the spleen (15-fold) and liver (8-fold), followed by intestine and gills to give 5.3-and 3.9-fold respectively. However, the lowest gene expression was detected in the kidney (2.5-fold).
from these results, we conclude that the spleen, liver, and kidney are the main target organs involved in the immune response during A. hydrophila infection in Nile tilapia. Also, gill plays an important role in early defense against A. hydrophila infection. IL-1β and IFN-γ are important pro-inflammatory cytokines against A. hydrophila infection in Nile tilapia.