Production and characterization of monoclonal antibodies against grass carp CD4-1 and CD4-2

CD4 T helper cells are an important group of cells in the immune system of vertebrates and express CD4 receptor on the cell surface. In mammals, the CD4 receptor is encoded by a single copy gene, whilst in fish, two copies of cd4 genes, namely cd4-1 and cd4-2, are found. In this study, the ectodomains of grass carp (Ctenopharyngodon idella, Ci) CD4-1 and CD4-2 were expressed in the E. coli cells and used to generate monoclonal antibodies in mice. Western blotting, confocal microscopy and flow cytometry were performed to characterize the monoclonal antibodies. It has been shown that the CiCD4-1 and CiCD4-2 monoclonal antibodies had good specificity to react with the recombinant ectodomains of CiCD4-1 and CiCD4-2 expressed in the CHO–S cells and the native CD4 molecules of grass carp. The CiCD4-1 monoclonal antibody did not recognize CiCD4-2 and verse versa. In addition, the CD4-1 and CD4-2 monoclonal antibodies specifically recognized the CD4-1 and CD4-2 receptors expressed in the HEK293 cells and native molecules of fish cells. Further, the percentages of lymphocytes in immune tissues of healthy fish were analyzed by flow cytometry. It was found that 17.6% of lymphocytes were CD4-1+ cells and 22.5% were CD4-2+ in the head kidney. In the spleen, 13.1% of lymphocytes were CD4-1+ and 18.6% were CD4-2+ while 7.3% of blood lymphocytes were CD4-1+ cells and 8.8% were CD4-2+ cells. The availability of the CD4-1 and CD4-2 monoclonal antibodies provides antibody-based tools for further elucidation of the functions of CD4 T cells in grass carp.