Identification and Characterization of Immunoglobulin T Heavy Chain in Large Yellow Croaker ( Larimichthys crocea )

• Published in: Fishes
• Main Authors: Yan Teng, Qiuling Fu, Yuanzhen Tan, Yangyang Ding, Yang Ding, Xinhua Chen
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: immunoglobulin T; large yellow croaker ( Larimichthys crocea ); expression modulation; parasitic infection; Biology (General); QH301-705.5; Genetics; QH426-470; Scophthalmus maximus
• Online Access: https://doi.org/10.3390/fishes7010029; https://doaj.org/article/99da23b2c23e46b093729ad1bb58cb02

Three immunoglobulin (Ig) isotypes have been identified in teleosts, IgM, IgD, and IgT or IgZ. IgT, a new teleost Ig isotype, plays a vital role in mucosal immunity. However, information on molecular and functional characteristics of fish IgT is still limited. In this study, an IgT heavy chain ( Lc IgT) gene was cloned and characterized in large yellow croaker ( Larimichthys crocea ). Complete cDNA of Lc IgT was 1930 bp in length, encoding a protein of 554 amino acids. The deduced Lc IgT contains a V H region and only three C H regions (C H 1, C H 2, C H 4), but no transmembrane region was predicted. Phylogenetic analysis showed that IgT heavy chain sequences from all fish species are grouped together. Homology comparison showed that Lc IgT shares the highest amino acid identity of 58.73% with IgT heavy chain in Scophthalmus maximus . The V H domain of Lc IgT has the highest identity of 72.50% with that of Scophthalmus maximus IgT. Relatively, each constant domain of Lc IgT exhibits the highest amino acid identity with that of IgT in Oreochromis niloticus (67.61% identity for C H 1, 61.11% identity for C H 2, and 63.74% identity for C H 4). Lc IgT was constitutively expressed in various tissues tested, with the highest levels in mucosa-associated tissues such as gills and skin. After Cryptocaryon irritans infection, the mRNA levels of Lc IgT were significantly up-regulated in the spleen (3.27-fold) at 4 d, in the head kidney (3.98-fold) and skin (2.11-fold) at 7 d, and in gills (4.45-fold) at 14 d. The protein levels in these detected tissues were all significantly up-regulated; the peak of its up-regulation was 6.33-fold at 28d in gills, 3.44-fold at 7d in skin, and 3.72-fold at 14d in spleen. These results showed that IgT response could be simultaneously induced in both systemic and mucosal tissues after parasitic infection and that IgT may be involved in systemic immunity and mucosal immunity against parasitic infection.