title: Antigen-dependent T lymphocytes (TcRβ+) are primarily differentiated in the thymus rather than in other lymphoid tissues in sea bass (Dicentrarchus labrax, L.).
abstract: All jawed vertebrates share lymphocyte receptors that allow the recognition of pathogens and the discrimination between self and non-self antigens. The T cell transmembrane receptor (TcR) has a central role in the maturation and function of T lymphocytes in vertebrates via an important role in positive selection of the variable region of TcR αβ/γδ chains. In this study, the TcRβ transcript expression and TcRβ(+) cell distribution during the ontogeny of the immune system of sea bass (Dicentrarchus labrax, L.) were analysed. RT-PCR analysis of larvae during early development demonstrated that the β chain transcript is expressed by 19 days post-fertilisation (p.f.). RNA probes specific for the β chain were synthesised and used for in situ hybridisation experiments on 30 day p.f. to 180 day old juvenile larvae. A parallel immunohistochemical study was performed using the anti-T cell monoclonal antibody DLT15 developed in our laboratory [Scapigliati et al., Fish Shellfish Immunol 1996; 6:383-401]. The first thymus anlage was detectable at 32-33 days p.f. (Corresponding to about 27 days post-hatch). DLT15(+) cells were detected at day 35 p.f. in the thymus whereas TcRβ(+) cells were recognisable at day 38 p.f. in the thymus and at day 41 p.f. in the gut. TcRβ(+) cells were observed in capillaries from 41 to 80 days p.f. At day 46 p.f., TcRβ(+) cells were identified in the head kidney and were detected in the spleen 4 days later. The present results demonstrate that TcRβ(+) cells can be differentiated first in the thymus and then in other organs/tissues, suggesting potential TcRβ(+) cell colonisation from the thymus to the middle gut. Once the epithelial architecture of the thymus is completed with the formation of the cortical-medullary border (around 70-75 days p.f.), DLT15(+) cells or TcRβ(+) cells are confined mainly to the cortex and cortical-medullary border. In particular, a large influx of TcRβ(+) cells was observed at the cortical-medullary border from 72 to 90 days p.f., suggesting a role in positive selection for this thymic region during the ontogeny of the fish immune system. This study provides novel information about the primary differentiation and distribution of TcRβ(+) cells in sea bass larvae and juveniles.
authors.affiliation: Department of Environmental Sciences, Tuscia University, Viterbo, Italy. nromano@unitus.it
authors.forename: Nicla
authors.initials: N
authors.lastname: Romano
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Caccia
authors.forename: Rita
authors.initials: R
authors.lastname: Piergentili
authors.forename: Francesca
authors.initials: F
authors.lastname: Rossi
authors.forename: Anna Grazia
authors.initials: AG
authors.lastname: Ficca
authors.forename: Sabrina
authors.initials: S
authors.lastname: Ceccariglia
authors.forename: Lucia
authors.initials: L
authors.lastname: Mastrolia
mesh_terms: D000818:Animals; D001492:Bass / Q000276:immunology*; D002454:Cell Differentiation; D008221:Lymphoid Tissue / Q000166:cytology; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013601:T-Lymphocytes / Q000166:cytology* / Q000378:metabolism*; D013950:Thymus Gland / Q000166:cytology*
chemical_list: D016693:Receptors, Antigen, T-Cell, alpha-beta