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

Yan Teng,Qiuling Fu,Yangyang Ding,Xinhua Chen,Yang Ding,Yuanzhen Tan

doi:10.3390/fishes7010029

Abstract

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 (LcIgT) gene was cloned and characterized in large yellow croaker (Larimichthys crocea). Complete cDNA of LcIgT was 1930 bp in length, encoding a protein of 554 amino acids. The deduced LcIgT contains a VH region and only three CH regions (CH1, CH2, CH4), 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 LcIgT shares the highest amino acid identity of 58.73% with IgT heavy chain in Scophthalmus maximus. The VH domain of LcIgT has the highest identity of 72.50% with that of Scophthalmus maximus IgT. Relatively, each constant domain of LcIgT exhibits the highest amino acid identity with that of IgT in Oreochromis niloticus (67.61% identity for CH1, 61.11% identity for CH2, and 63.74% identity for CH4). LcIgT 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 LcIgT 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.

Highlights

IntroductionImmunoglobulins (Igs) consist of two light (L) chains and two heavy (H) chains [1], which have a critical role in the vertebrate adaptive immune system as an important class of immune effector molecules
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
Expression analyses showed that large yellow croaker IgT heavy chain (LcIgT) was constitutively expressed in all tissues tested, with the highest levels in gills (Figure 5), which was consistent with the results observed in trout [30], flounder [13], European seabass [15], blunt snout bream [42], and emerald rock cod [43]

Summary

Introduction

Immunoglobulins (Igs) consist of two light (L) chains and two heavy (H) chains [1], which have a critical role in the vertebrate adaptive immune system as an important class of immune effector molecules. Five Igs isotypes have been identified in mammals: IgM, IgG, IgA, IgD, and IgE, based on the difference of heavy chain [2]. Only three Igs isotypes, IgM, IgD, and IgT or IgZ are discovered as yet [3,4,5,6,7]. IgM is the most predominant and stable Ig in systemic immunity, while IgT or IgZ is considered an Ig specialized in mucosal immunity in teleosts [8]. IgD has an unknown function in teleosts, but studies have suggested that IgD might be involved in surveillance and immune regulation as an antigen-binding receptor [9]

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Discussion

Conclusion