Molecular, Cellular and Functional Analysis of TR gamma Chain along the European Sea Bass Dicentrarchus labrax Development

In jawed vertebrates, adaptive immune responses are enabled by T cells. Two lineages were characterized based on their T cell receptor (TcR) heterodimers, namely alpha beta or gamma delta peptide chains, which display an Ig domain-type sequence that is somatically rearranged. gamma delta T cells have been less extensively characterized than alpha beta and teleost fish, in particular, suffer from a severe scarcity of data. In this paper, we worked on the well-known model, the European sea bass Dicentrarchus labrax, to broaden the understanding of teleost gamma delta-T cells. The T cell receptor chain (TR) gamma transcript was expressed at a later developmental stage than TR beta, suggesting a layered appearance of fish immune cells, and the thymus displayed statistically-significant higher mRNA levels than any other organ or lymphoid tissue investigated. The polyclonal antibody developed against the TR gamma allowed the localization of TR gamma-expressing cells in lymphoid organs along the ontogeny. Cell positivity was investigated through flow cytometry and the highest percentage was found in peripheral blood leukocytes, followed by thymus, gut, gills, spleen and head kidney. Numerous TR gamma-expressing cells were localized in the gut mucosa, and the immunogold labelling revealed ultrastructural features that are typical of T cells. At last, microalgae-based diet formulations significantly modulated the abundance of TR gamma(+) cells in the posterior intestine, hinting at a putative involvement in nutritional immunity. From a comparative immunological perspective, our results contribute to the comprehension of the diversity and functionalities of gamma delta T cells during the development of a commercially relevant marine teleost model.