RESUMO
Gammadelta T cells localize at mammalian epithelial surfaces to exert both protective and regulatory roles in response to infections. We have previously characterized the Mexican axolotl (Ambystoma mexicanum) T cell receptor delta (TRD) chain. In this study, TRD repertoires in spleen, liver, intestine and skin from larvae, pre-adult and adult axolotls were examined and compared to the thymic TRD repertoire. A TRDV transcript without N/D diversity, TRDV1S1-TRDJ1, dominates the TRD repertoires until sexual maturation. In adult tissues, this canonical transcript is replaced by another dominant TRDV1S1-TRDJ1 transcript. In the thymus, these two transcripts are detected early in development. Our results suggest that gammadelta T cells that express the canonical TRDV1S1-TRDJ1 transcript emerge from the thymus and colonize the peripheral tissues, where they are selectively expanded by recurrent ligands. This particular situation is probably related to the neotenic state and the slow development of the axolotl. In thymectomized axolotls, TRD repertoires appear different from those of normal axolotls, suggesting that extrathymic gammadelta T cell differentiation could occur. Gene expression analysis showed the importance of the gut in T cell development.
Assuntos
Rearranjo Gênico da Cadeia delta dos Receptores de Antígenos dos Linfócitos T , Sistema Imunitário/crescimento & desenvolvimento , Receptores de Antígenos de Linfócitos T gama-delta/genética , Ambystoma mexicanum , Sequência de Aminoácidos , Animais , Sequência de Bases , Diferenciação Celular , DNA Nucleotidilexotransferase/genética , Fator de Transcrição GATA3/genética , Expressão Gênica , Proteínas de Homeodomínio/genética , Fator de Transcrição Ikaros/genética , Sistema Imunitário/imunologia , Sistema Imunitário/metabolismo , Hibridização In Situ , Mucosa Intestinal/metabolismo , Intestinos/crescimento & desenvolvimento , Intestinos/imunologia , Larva/crescimento & desenvolvimento , Larva/imunologia , Larva/metabolismo , Fígado/crescimento & desenvolvimento , Fígado/imunologia , Fígado/metabolismo , Dados de Sequência Molecular , Receptores de Antígenos de Linfócitos T alfa-beta/genética , Receptores de Antígenos de Linfócitos T gama-delta/análise , Receptores de Antígenos de Linfócitos T gama-delta/imunologia , Alinhamento de Sequência , Pele/crescimento & desenvolvimento , Pele/imunologia , Pele/metabolismo , Baço/crescimento & desenvolvimento , Baço/imunologia , Baço/metabolismo , Linfócitos T/citologia , Linfócitos T/imunologia , Linfócitos T/metabolismo , Timo/crescimento & desenvolvimento , Timo/imunologia , Timo/metabolismoRESUMO
Mammals and birds have two major populations of T cells, based on the molecular composition and biological properties of their antigen receptors (TCR). alpha beta T cells recognize antigenic peptides linked to major histocompatibility complex (MHC) molecules, and gamma delta T cells recognize native peptide or non-peptide antigens independently of MHC. Very little is known about gamma delta T cells in ectothermic vertebrates. We have cloned and characterized the TCRdelta chains of an urodele amphibian, the Mexican axolotl (Ambystoma mexicanum). The Cdelta domain is structurally similar to its mammalian homologues and the transmembrane domain is very well conserved. Four of the six Valpha regions that can associate with Calpha (Valpha2, Valpha3, Valpha5 and Valpha6) can also associate with Cdelta, but no specific Vdelta regions were found. This suggests that the axolotl TRD locus is nested within the TRA locus, as in mammals, and that this organization has been present in all tetrapod vertebrates and in the common ancestor of Lissamphibians and mammals, for over 400 million years. Two Jdelta regions were identified, but no Ddelta segments were clearly recognized at the Vdelta-Jdelta junctions. This results in shorter and less variable CDR3 loops than in other vertebrates and the size range of the Vdelta-Jdelta junctions is similar to that of mammalian immunoglobulin light chains. Equivalent quantities of TRD mRNA were found in the lymphoid organs, and in the skin and the intestines of normal and thymectomized axolotls. The analysis of several Valpha/delta6-Cdelta and Vbeta7-Cbeta junctions showed that both the TCRdelta and the TCRbeta chains were limited in diversity in thymectomized axolotls.