الفهرس 
Nile tilapia
Cytokines involved in adaptive immunityOnly 14 pages are availabe for public view
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Abstract
Infection of Nile tilapia (Oreochromis niloticus) by Aeromonas hydrophila (A. hydrophila) causes hemorrhagic septicemia which is accompanied by high rate of mortality and economic losses. The current available treatment of this bacterium and other bacteria is the antimicrobial drugs which when used in large doses and for long time may lead to depression of fish immunity, growth and their residues can negatively affect consumers and the environment. Enhancing fish immunity in aquaculture is the main target of many fish farms. Among different immunity related molecules, the major histocompatibility complex (MHC, especially class IIA) come on the top for their role in presenting antigens to T cell receptors. The aim of this work was to search for polymorphisms in MHCIIA gene in A.hydrophila-challenged Nile tilapia and to study their association with immunity through investigating immunity–related biochemical parameters, oxidative stress/antioxidants parameters and MHCIIA gene expression. Nile tilapia (n = 120) with average size between 70 and 90 g were obtained from local farms in Kafr El sheikh and Edfina. After 2 weeks of acclimation, fish were intraperitoneally injected by A.hydrophila to get two divergent lines of fish in response to disease: one susceptible/diseased and the other resistant to disease. The Association between G23T SNP and immunity-related parameters were evaluated by determination the changes in immunity parameter such as (total protein, globulin, IgM, phagocytic activity, phagocytic index, lysozyme activity),the association with oxidative stress as MDA and antioxidant enzymes (catalase, glutathione peroxidase, superoxide dismutase) activities, and finally the association with MHCIIA gene expression in spleen. The obtained results were summarized as follow: Three different SSCP banding patterns were detected in the three fish groups. SSCP results were further confirmed and the SNP was identified by sequencing. The obtained sequences were submitted to Gene Bank databases with the following accession numbers: MF490449 and MF490450. Analysis of these sequences revealed presence of a nonsynonymous G23T SNP at nucleotide number 23 of MHC IIA locus where G replaced T. Interestingly; this SNP changed the stop codon to glycine (G) amino acid. Subsequently, the stop codon was right shifted 33 nucleotides downstream of glycine in 3’UTR. Nucleotide alignment between the two sequences revealed nucleotide sequences identity of 80% in addition to different types of gene polymorphisms including deletion, insertion, and SNPs. The frequency of TT was higher in resistant fish than GG, however in susceptible fish; GG genotype was higher than TT. Consequently, the frequency of G allele was significantly higher in susceptible fish than resistant fish, suggesting that G may be the risk (recessive or mutant) allele for susceptibility to A. hydrophila infection. All immunity parameters significantly increased in the resistant fish than the control and susceptible fish, except albumin which showed non-significant increase. On the other hand, susceptible fish exhibited non-significant changes in these parameters as compared to control fish, except for PA, PI, lysozyme activity which was significantly elevated in susceptible than control fish. Among the three genotypes in all fish, TT fish had a significant higher level of these parameters than heterozygous (TG) fish then homozygous GG fish. The antioxidant enzymes (CAT, GPX and SOD) activities in spleen were significantly increased in the control and resistant fish than the susceptible fish. However, the lipid peroxidation marker MDA level in spleen was significantly increased in susceptible fish than the control and resistant fish. Again, TT fish had a significant higher CAT, GPX and SOD than GG fish but GG fish had a significant higher MDA than TT fish. The expression level of MHC IIA gene in spleen was significantly (P < 0.05) higher in resistant fish than normal and susceptible fish. Notably, susceptible fish also showed a significant up regulated expression as compared to control fish. Moreover, the expression level was significantly higher in TT fish followed by TG and then GG fish.