| Intercellular adhesion molecule-1(ICAM-1,CD54)is a transmembrane surface glycoprotein expressed in endothelial cells,epithelial cells,immune cells and other cell types,mainly mediating cell-cell interaction.ICAM-1 is normally expressed at low levels in all cell types,but is upregulated under inflammatory conditions.Rainbow trout(Oncorhynchus mykiss)is a salmonid fish that is widely farmed in freshwater and seawater in many parts of the world and is loved for its delicious meat.However,the frequent invasion of many pathogens,such as viruses,bacteria and parasites,threatens the sustainable and healthy development of rainbow trout breeding and hinders the economic progress of rainbow trout breeding in China.Therefore,the study on the immune mechanism of rainbow trout against pathogen infection will play a positive role in promoting the development of rainbow trout breeding industry.In this study,we cloned and characterized the sequence of ICAM-1 in rainbow trout for the first time.Moreover,the differential expression of ICAM-1 m RNA was assessed in different tissues of trout including mucosal tissues,non-mucosal tissues,and systemic tissues.Additionally,we investigated ICAM-1-mediated immune responses in rainbow trout challenged with viral,bacterial,and parasitic infections.Morphological changes were observed in the skin and gills of organisms infected with infectious hematopoietic necrosis virus(IHNV;i.e.,a virus),Flavobacterium columnare G4(F.columnare;i.e.,a bacterium),and Ichthyophthirius multifiliis(Ich;i.e.,a parasite),which coincided with changes in ICAM-1 gene expression in both systemic and mucosal tissues.Therefore,our findings provide important insights into the predominant role of the ICAM-1 gene in the mucosal immune responses to viral,bacterial,and parasitic infections in teleost fish.The specific experimental results of this study are as follows:(1)The full-length sequence of rainbow trout ICAM-1 was amplified by RACEPCR,and the sequence analysis found that the full-length sequence of rainbow trout ICAM-1 was 1958 bp,of which the open reading frame(ORF)was 1095 bp,encoding365 amino acid and structural analysis showed that the rainbow trout ICAM-1 sequence has a signal peptide,an immunoglobulin-like domain(Ig-like domain),a transmembrane domain and a free cysteine,which is similar in structure of other teleost fish.(2)Through the sequence alignment and evolution analysis of ICAM-1,we found that ICAM-1 of rainbow trout is closely related to ICAM-1 of Salmonidae,followed by Cyprinidae.(3)By qPCR,we detected the m RNA expression of rainbow trout ICAM-1 in 12 tissues of rainbow trout including liver,stomach,intestine,eye,muscle,oral mucosa,skin,nose,pharynx,gill,spleen,and head kidney(HK).The highest expression level of ICAM-1 gene was found in the HK,and spleen of systemic tissues,while lower expression level was observed in the liver,and stomach,in addition,we found that in mucosal tissues,ICAM-1 had higher expression levels expression,suggesting that ICAM-1 might play an important role in mucosal tissue.(4)To this end,we constructed three infection models of viruses,bacteria,and parasites infecting rainbow trout.Through HE staining and q PCR,we detected the pathological changes and pathogen load of mucosal tissue and systemic tissue after pathogenic infection to indicate that the infection model was built successfully.Further,by q PCR,we detected the expression of ICAM-1 in systemic tissues and mucosal tissues after pathogen infection.We found that after viral,bacterial,and parasitic infections,the expression of ICAM-1 in systemic and mucosal tissues was significantly increased.There is a significant increasing trend,especially in mucosal tissue.This suggests that ICAM-1 plays an important role in the mucosal immunity of rainbow trout against pathogenic infection. |
