A molecular threshold for effector CD8(+) T cell differentiation controlled by transcription factors Blimp-1 and T-bet.

T cell responses are guided by cytokines that induce transcriptional regulators, which ultimately control differentiation of effector and memory T cells. However, it is unknown how the activities of these molecular regulators are coordinated and integrated during the differentiation process. Using genetic approaches and transcriptional profiling of antigen-specific CD8(+) T cells, we reveal a common program of effector differentiation that is regulated by IL-2 and IL-12 signaling and the combined activities of the transcriptional regulators Blimp-1 and T-bet. The loss of both T-bet and Blimp-1 leads to abrogated cytotoxic function and ectopic IL-17 production in CD8(+) T cells. Overall, our data reveal two major overlapping pathways of effector differentiation governed by the availability of Blimp-1 and T-bet and suggest a model for cytokine-induced transcriptional changes that combine, quantitatively and qualitatively, to promote robust effector CD8(+) T cell differentiation.

Protective function and differentiation cues of brain-resident CD8+ T cells during surveillance of latent Toxoplasma gondii infection.

Chronic Toxoplasma gondii infection induces brain-resident CD8+ T cells (bTr), but the protective functions and differentiation cues of these cells remain undefined. Here, we used a mouse model of latent infection by T. gondii leading to effective CD8+ T cell-mediated parasite control. Thanks to antibody depletion approaches, we found that peripheral circulating CD8+ T cells are dispensable for brain parasite control during chronic stage, indicating that CD8+ bTr are able to prevent brain parasite reactivation. We observed that the retention markers CD69, CD49a, and CD103 are sequentially acquired by brain parasite-specific CD8+ T cells throughout infection and that a majority of CD69/CD49a/CD103 triple-positive (TP) CD8+ T cells also express Hobit, a transcription factor associated with tissue residency. This TP subset develops in a CD4+ T cell-dependent manner and is associated with effective parasite control during chronic stage. Conditional invalidation of Transporter associated with Antigen Processing (TAP)-mediated major histocompatibility complex (MHC) class I presentation showed that presentation of parasite antigens by glutamatergic neurons and microglia regulates the differentiation of CD8+ bTr into TP cells. Single-cell transcriptomic analyses revealed that resistance to encephalitis is associated with the expansion of stem-like subsets of CD8+ bTr. In summary, parasite-specific brain-resident CD8+ T cells are a functionally heterogeneous compartment which autonomously ensure parasite control during T. gondii latent infection and which differentiation is shaped by neuronal and microglial MHC I presentation. A more detailed understanding of local T cell-mediated immune surveillance of this common parasite is needed for harnessing brain-resident CD8+ T cells in order to enhance control of chronic brain infections.

T-box Transcription Factors Combine with the Cytokines TGF-ß and IL-15 to Control Tissue-Resident Memory T Cell Fate.

Tissue-resident memory T (Trm) cells contribute to local immune protection in non-lymphoid tissues such as skin and mucosa, but little is known about their transcriptional regulation. Here we showed that CD8(+)CD103(+) Trm cells, independent of circulating memory T cells, were sufficient for protection against infection and described molecular elements that were crucial for their development in skin and lung. We demonstrated that the T-box transcription factors (TFs) Eomes and T-bet combined to control CD8(+)CD103(+) Trm cell formation, such that their coordinate downregulation was crucial for TGF-ß cytokine signaling. TGF-ß signaling, in turn, resulted in reciprocal T-box TF downregulation. However, whereas extinguishment of Eomes was necessary for CD8(+)CD103(+) Trm cell development, residual T-bet expression maintained cell surface interleukin-15 (IL-15) receptor ß-chain (CD122) expression and thus IL-15 responsiveness. These findings indicate that the T-box TFs control the two cytokines, TGF-ß and IL-15, which are pivotal for CD8(+)CD103(+) Trm cell development and survival.

The transcription factors Blimp-1 and IRF4 jointly control the differentiation and function of effector regulatory T cells.

Regulatory T cells (T(reg) cells) are required for peripheral tolerance. Evidence indicates that T(reg) cells can adopt specialized differentiation programs in the periphery that are controlled by transcription factors usually associated with helper T cell differentiation. Here we demonstrate that expression of the transcription factor Blimp-1 defined a population of T(reg) cells that localized mainly to mucosal sites and produced IL-10. Blimp-1 was required for IL-10 production by these cells and for their tissue homeostasis. We provide evidence that the transcription factor IRF4, but not the transcription factor T-bet, was essential for Blimp-1 expression and for the differentiation of all effector T(reg) cells. Thus, our study defines a differentiation pathway that leads to the acquisition of T(reg) cell effector functions and requires both IRF4 and Blimp-1.

Influenza vaccination induces autoimmunity against orexinergic neurons in a mouse model for narcolepsy.

Narcolepsy with cataplexy or narcolepsy type 1 is a disabling chronic sleep disorder resulting from the destruction of orexinergic neurons in the hypothalamus. The tight association of narcolepsy with HLA-DQB1*06:02 strongly suggest an autoimmune origin to this disease. Furthermore, converging epidemiological studies have identified an increased incidence for narcolepsy in Europe following Pandemrix® vaccination against the 2009-2010 pandemic 'influenza' virus strain. The potential immunological link between the Pandemrix® vaccination and narcolepsy remains, however, unknown. Deciphering these mechanisms may reveal pathways potentially at play in most cases of narcolepsy. Here, we developed a mouse model allowing to track and study the T-cell response against 'influenza' virus haemagglutinin, which was selectively expressed in the orexinergic neurons as a new self-antigen. Pandemrix® vaccination in this mouse model resulted in hypothalamic inflammation and selective destruction of orexin-producing neurons. Further investigations on the relative contribution of T-cell subsets in this process revealed that haemagglutinin-specific CD4 T cells were necessary for the development of hypothalamic inflammation, but insufficient for killing orexinergic neurons. Conversely, haemagglutinin-specific CD8 T cells could not initiate inflammation but were the effectors of the destruction of orexinergic neurons. Additional studies revealed pathways potentially involved in the disease process. Notably, the interferon-γ pathway was proven essential, as interferon-γ-deficient CD8 T cells were unable to elicit the loss of orexinergic neurons. Our work demonstrates that an immunopathological process mimicking narcolepsy can be elicited by immune cross-reactivity between a vaccine antigen and a neuronal self-antigen. This process relies on a synergy between autoreactive CD4 and CD8 T cells for disease development. This work furthers our understanding of the mechanisms and pathways potentially involved in the development of a neurological side effect due to a vaccine and, likely, to narcolepsy in general.

Interleukin-2 tickles T cell memory.

The differentiation of peripheral T lymphocytes depends on interactions between intrinsic and extrinsic factors. In this issue of Immunity, Pipkin et al. (2010) and Kalia et al. (2010) link differential interleukin-2 signaling and inflammation with the transcriptional events leading to the development of effector and memory cells.

Id2 represses E2A-mediated activation of IL-10 expression in T cells.

Interleukin-10 (IL-10) is a key immunoregulatory cytokine that functions to prevent inflammatory and autoimmune diseases. Despite the critical role for IL-10 produced by effector CD8(+) T cells during pathogen infection and autoimmunity, the mechanisms regulating its production are poorly understood. We show that loss of the inhibitor of DNA binding 2 (Id2) in T cells resulted in aberrant IL-10 expression in vitro and in vivo during influenza virus infection and in a model of acute graft-versus-host disease (GVHD). Furthermore, IL-10 overproduction substantially reduced the immunopathology associated with GVHD. We demonstrate that Id2 acts to repress the E2A-mediated trans-activation of the Il10 locus. Collectively, our findings uncover a key regulatory role of Id2 during effector T cell differentiation necessary to limit IL-10 production by activated T cells and minimize their suppressive activity during the effector phase of disease control.

Id2 expression delineates differential checkpoints in the genetic program of CD8α+ and CD103+ dendritic cell lineages.

Dendritic cells (DCs) have critical roles in the induction of the adaptive immune response. The transcription factors Id2, Batf3 and Irf-8 are required for many aspects of murine DC differentiation including development of CD8α(+) and CD103(+) DCs. How they regulate DC subset specification is not completely understood. Using an Id2-GFP reporter system, we show that Id2 is broadly expressed in all cDC subsets with the highest expression in CD103(+) and CD8α(+) lineages. Notably, CD103(+) DCs were the only DC able to constitutively cross-present cell-associated antigens in vitro. Irf-8 deficiency affected loss of development of virtually all conventional DCs (cDCs) while Batf3 deficiency resulted in the development of Sirp-α(-) DCs that had impaired survival. Exposure to GM-CSF during differentiation induced expression of CD103 in Id2-GFP(+) DCs. It did not restore cross-presenting capacity to Batf3(-/-) or CD103(-)Sirp-α(-)DCs in vitro. Thus, Irf-8 and Batf3 regulate distinct stages in DC differentiation during the development of cDCs. Genetic mapping DC subset differentiation using Id2-GFP may have broad implications in understanding the interplay of DC subsets during protective and pathological immune responses.

TCF-1 controls ILC2 and NKp46+RORγt+ innate lymphocyte differentiation and protection in intestinal inflammation.

Innate lymphocyte populations play a central role in conferring protective immunity at the mucosal frontier. In this study, we demonstrate that T cell factor 1 (TCF-1; encoded by Tcf7), a transcription factor also important for NK and T cell differentiation, is expressed by multiple innate lymphoid cell (ILC) subsets, including GATA3(+) nuocytes (ILC2) and NKp46(+) ILCs (ILC3), which confer protection against lung and intestinal inflammation. TCF-1 was intrinsically required for the differentiation of both ILC2 and NKp46(+) ILC3. Loss of TCF-1 expression impaired the capacity of these ILC subsets to produce IL-5, IL-13, and IL-22 and resulted in crippled responses to intestinal infection with Citrobacter rodentium. Furthermore, a reduction in T-bet expression required for Notch-2-dependent development of NKp46(+) ILC3 showed a dose-dependent reduction in TCF-1 expression. Collectively, our findings demonstrate an essential requirement for TCF-1 in ILC2 differentiation and reveal a link among Tcf7, Notch, and Tbx21 in NKp46(+) ILC3 development.

Id2-mediated inhibition of E2A represses memory CD8+ T cell differentiation.

The transcription factor inhibitor of DNA binding (Id)2 modulates T cell fate decisions, but the molecular mechanism underpinning this regulation is unclear. In this study we show that loss of Id2 cripples effector differentiation and instead programs CD8(+) T cells to adopt a memory fate with increased Eomesodermin and Tcf7 expression. We demonstrate that Id2 restrains CD8(+) T cell memory differentiation by inhibiting E2A-mediated direct activation of Tcf7 and that Id2 expression level mirrors T cell memory recall capacity. As a result of the defective effector differentiation, Id2-deficient CD8(+) T cells fail to induce sufficient Tbx21 expression to generate short-lived effector CD8(+) T cells. Our findings reveal that the Id2/E2A axis orchestrates T cell differentiation through the induction or repression of downstream transcription factors essential for effector and memory T cell differentiation.