The Immune Response Of IgM And IgT In Large Yellow Croaker Against Cryptocaryon Irritans Infection

Large yellow croaker(Larimichthys crocea),an important marine economic fish species in my country,is listed as one of the eight most advantageous export aquatic products by the Ministry of Agriculture.With the rapid development of the large yellow croaker aquaculture industry in recent years,diseases of large yellow croaker are becoming more and more serious.White-spot disease from skin surface caused by Cryptocaryon irritans(C.irritans)infection is one of the most serious diseases in large yellow croaker industry,however,there is no safe and effective methods to control it.In recent years,immune control measures have received extensive attention.The research on the immune system and its function of large yellow croaker is particularly important to prevent and control the diseases of large yellow croaker effectively.Immunoglobulin(Ig),the main effector molecule of fish humoral immune response,plays an important role in fish immunity.However,the function of IgM and IgT in C.irritans infection is still unknown.In this study,we established an artificial infection model of C.irritans in large yellow croaker,and analyzed the transcription level and protein level changes of IgM and IgT and B cell proliferation in the head kidney,spleen and peripheral blood of large yellow croaker after C.irritans infection.Specific research results are as follows:1.The transcriptional levels of IgM and IgT heavy chain genes in different tissues of healthy large yellow croaker were studied,and found that IgM and IgT heavy chain genes were constitutively expressed in different tissues.IgM heavy chain genes had the highest expression in skin and the lowest expression in peripheral blood,while the expression of IgT heavy chain gene was highest in gill and lowest in peripheral blood.2.The transcriptional levels of IgM and IgT heavy chain genes in the head kidney and spleen of large yellow croaker after C.irritans infection were studied.It was found that the IgM heavy chain genes in the head kidney were significantly up regulated after 7 and 60 d infection,and that the IgT heavy chain genes were significantly up regulated after 7 d infection.In spleen,IgM heavy chain gene was significantly up regulated after 4 and 60 d infection,IgT heavy chain gene was significantly upregulated after 4 and 21 d infection.3.The protein level changes of IgM and IgT in the head kidney and spleen were studied after C.irritans infection.IgM protein in the head kidney increased significantly after 28 d infection,while IgT protein increased significantlyafter 4,7 and 35 d infection.In addition,in spleen,IgM proteinincreased significantly after 4,7 and 42 d infection,while IgT protein increased significantly after 21 d infection.4.The protein concentrations of IgM and IgT large yellow croaker in serum after infection were studied.The concentration of IgM in serum increased significantly after 4 and 7 d infection,but the concentration of C.irritans-specific IgM was only increased significantly after 4 d infection.The concentration of IgT in serum increased significantly after 42 and 60d infection,while the concentration of C.irritans-specific IgT was increased significantly after 49 and 60 d infection.5.The proliferation of IgM~+B and IgT~+B cells in the head kidney,spleen and peripheral blood of large yellow croaker after C.irritans infection was studied.IgM~+B and IgT~+B cells proliferated significantly in peripheral blood after 7 d infection and in the head kidney after 21 d infection.In addition,IgT~+B cells proliferated significantly in spleen after35 d infection.and IgM~+B cells proliferated significantly in the head kidney after 49 d infection.In summary,this study indicated that IgM and IgT of large yellow croaker play an important role in C.irritans infection.It is not only great significance for further understandingthe immune mechanism of fish against C.irritans infection,but also provides theoretical basis for the design of efficiency vaccines against C.irritans.