Histone Acetylation at theIfngPromoter in Tolerized CD4 Cells Is Associated with Increased IFN-γ Expression during Subsequent Immunization to the Same Antigen

Abstract

When naive CD4+ Th cells encounter cognate pathogen-derived Ags they expand and develop the capacity to express the appropriate effector cytokines for neutralizing the pathogen. Central to this differentiation process are epigenetic modifications within the effector cytokine genes that allow accessibility to the transcriptional machinery. In contrast, when mature self-reactive CD4 cells encounter their cognate epitopes in the periphery they generally undergo a process of tolerization in which they become hyporesponsive/anergic to antigenic stimulation. In the current study, we used a TCR transgenic adoptive transfer system to demonstrate that in a dose-dependent manner parenchymal self-Ag programs cognate naive CD4 cells to acetylate histones bound to the promoter region of the Ifng gene (which encodes the signature Th1 effector cytokine) during peripheral tolerization. Although the Ifng gene gains transcriptional competence, these tolerized CD4 cells fail to express substantial amounts of IFN-γ in response to antigenic stimulation apparently because a blockage in TCR-mediated signaling also develops. Nevertheless, responsiveness to antigenic stimulation is partially restored when self-Ag-tolerized CD4 cells are retransferred into mice infected with a virus expressing the same Ag. Additionally, there is preferential boosting in the ability of these CD4 cells to express IFN-γ relative to other cytokines with expression that also becomes impaired. Taken together, these results suggest that epigenetic modification of the Ifng locus during peripheral CD4 cell tolerization might allow for preferential expression of IFN-γ during recovery from tolerance.

Self-Antigen Prevents CD8 T Cell Effector Differentiation by CD134 and CD137 Dual Costimulation

“…To thus assess whether the inability of enforced costimulation to redirect tolerogenic anti-self CD8 cell responses toward effector differentiation is the consequence of a specific peculiarity of our C3-HA-transgenic system that precludes effector T cell function, we tested the response of cognate CD4 cells in this system. As previously observed (52), adoptively transferred 6.5 TCR-transgenic HA-specific CD4 cells recovered from spleens of self-HA recipients only expressed minimal amounts of IFN- γ and TNF- α following restimulation with HA peptide (Fig. 5B).…”

“…7 and Fig. 1), this result suggested that in contrast to CD4 cells (52) the level of PMA plus I-induced IFN- γ expression may not always reflect the extent of Ifng locus remodeling in tolerized CD8 cells.…”

“…Thus, when naive 6.5 HA-specific TCR-transgenic CD4 cells are adoptively transferred into C3-HA-transgenic mice that express HA as a generic parenchymal self-Ag (self-HA), they initially proliferate and partially remodel their Ifng loci toward an open configuration, but ultimately develop an anergic phenotype. In contrast, when the same TCR-transgenic CD4 cells are transferred into NT mice infected with a recombinant vaccinia virus expressing HA (viral HA), they proliferate and differentiate into Th1 effectors (40, 52). …”

The E3 Ubiquitin Ligase Cbl-b Regulates Expansion but Not Functional Activity of Self-Reactive CD4 T Cells

“…), as previously described (50, 53). Adoptive retransfers were performed, as previously described (54). …”

“…5 of Ref. 54) were analyzed by quantitative SYBR Green-based real-time RT-PCR, as previously described (55). Briefly, after reverse transcribing cDNA, T-bet and Cbl-b mRNAs were quantified by first normalizing for input sample amounts by calculating the difference in threshold cycle (C T ) values relative to hypoxanthine phosphoribosyltransferase, and then using the ΔΔC T method to calculate the ratio between experimental samples and a representative naive CD4 T cell sample.…”