RESUMO
Recent thymic emigrants (RTEs) are the youngest T cells in the lymphoid periphery and exhibit phenotypic and functional characteristics distinct from those of their more mature counterparts in the naive peripheral T cell pool. We show in this study that the Il2 and Il4 promoter regions of naive CD4(+) RTEs are characterized by site-specific hypermethylation compared with those of both mature naive (MN) T cells and the thymocyte precursors of RTEs. Thus, RTEs do not merely occupy a midpoint between the thymus and the mature T cell pool, but represent a distinct transitional T cell population. Furthermore, RTEs and MN T cells exhibit distinct CpG DNA methylation patterns both before and after activation. Compared with MN T cells, RTEs express higher levels of several enzymes that modify DNA methylation, and inhibiting methylation during culture allows RTEs to reach MN T cell levels of cytokine production. Collectively, these data suggest that the functional differences that distinguish RTEs from MN T cells are influenced by epigenetic mechanisms and provide clues to a mechanistic basis for postthymic maturation.
Assuntos
Diferenciação Celular/genética , Citocinas/genética , Metilação de DNA/imunologia , Subpopulações de Linfócitos T/citologia , Linfócitos T/citologia , Timócitos/citologia , Animais , Diferenciação Celular/imunologia , Separação Celular , Citocinas/imunologia , Metilação de DNA/genética , Citometria de Fluxo , Interleucina-2/genética , Interleucina-4/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Regiões Promotoras Genéticas/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Subpopulações de Linfócitos T/imunologia , Linfócitos T/imunologia , Timócitos/imunologiaRESUMO
TCR revision is a tolerance mechanism by which self-reactive TCRs expressed by mature CD4(+) peripheral T cells are replaced by receptors encoded by genes generated by post-thymic DNA rearrangement. The downmodulation of surface TCR expression initiates TCR revision, and serves as a likely trigger for the induction of the recombinase machinery. We show here in a Vß5 transgenic mouse model system that downregulation of the self-reactive transgene-encoded TCR is not maintained by transgene loss or diminished transcription or translation. The downregulation of surface TCR expression likely occurs in two stages, only one of which requires tolerogen expression.
Assuntos
Rearranjo Gênico da Cadeia beta dos Receptores de Antígenos dos Linfócitos T , Receptores de Antígenos de Linfócitos T alfa-beta/biossíntese , Receptores de Antígenos de Linfócitos T alfa-beta/genética , Animais , Linfócitos T CD4-Positivos/metabolismo , Regulação para Baixo/genética , Expressão Gênica/genética , Tolerância Imunológica/genética , Camundongos , Camundongos Transgênicos , Receptores de Antígenos de Linfócitos T alfa-beta/metabolismo , Transgenes/genéticaRESUMO
Peripheral CD4(+)Vß5(+) T cells are tolerized to an endogenous mouse mammary tumor virus superantigen either by deletion or TCR revision. Through TCR revision, RAG reexpression mediates extrathymic TCRß rearrangement and results in a population of postrevision CD4(+)Vß5(-) T cells expressing revised TCRß chains. We have hypothesized that cell death pathways regulate the selection of cells undergoing TCR revision to ensure the safety and utility of the postrevision population. In this study, we investigate the role of Bcl-2-interacting mediator of cell death (Bim)-mediated cell death in autoantigen-driven deletion and TCR revision. Bim deficiency and Bcl-2 overexpression in Vß5 transgenic (Tg) mice both impair peripheral deletion. Vß5 Tg Bim-deficient and Bcl-2 Tg mice exhibit an elevated frequency of CD4(+) T cells expressing both the transgene-encoded Vß5 chain and a revised TCRß chain. We now show that these dual-TCR-expressing cells are TCR revision intermediates and that the population of RAG-expressing, revising CD4(+) T cells is increased in Bim-deficient Vß5 Tg mice. These findings support a role for Bim and Bcl-2 in regulating the balance of survival versus apoptosis in peripheral T cells undergoing RAG-dependent TCR rearrangements during TCR revision, thereby ensuring the utility of the postrevision repertoire.
