ATP Binding Cassette Transporter ABCA7 Regulates NKT Cell Development and Function by Controlling CD1d Expression and Lipid Raft Content.

ABCA7 is an ABC transporter expressed on the plasma membrane, and actively exports phospholipid complexes from the cytoplasmic to the exocytoplasmic leaflet of membranes. Invariant NKT (iNKT) cells are a subpopulation of T lymphocytes that recognize glycolipid antigens in the context of CD1d-mediated antigen presentation. In this study, we demonstrate that ABCA7 regulates the development of NKT cells in a cell-extrinsic manner. We found that in Abca7-/- mice there is reduced expression of CD1d accompanied by an alteration in lipid raft content on the plasma membrane of thymocytes and antigen presenting cells. Together, these alterations caused by absence of ABCA7 negatively affect NKT cell development and function.

ABC transporters and NR4A1 identify a quiescent subset of tissue-resident memory T cells.

Immune surveillance in tissues is mediated by a long-lived subset of tissue-resident memory T cells (Trm cells). A putative subset of tissue-resident long-lived stem cells is characterized by the ability to efflux Hoechst dyes and is referred to as side population (SP) cells. Here, we have characterized a subset of SP T cells (Tsp cells) that exhibit a quiescent (G0) phenotype in humans and mice. Human Trm cells in the gut and BM were enriched in Tsp cells that were predominantly in the G0 stage of the cell cycle. Moreover, in histone 2B-GFP mice, the 2B-GFP label was retained in Tsp cells, indicative of a slow-cycling phenotype. Human Tsp cells displayed a distinct gene-expression profile that was enriched for genes overexpressed in Trm cells. In mice, proteins encoded by Tsp signature genes, including nuclear receptor subfamily 4 group A member 1 (NR4A1) and ATP-binding cassette (ABC) transporters, influenced the function and differentiation of Trm cells. Responses to adoptive transfer of human Tsp cells into immune-deficient mice and plerixafor therapy suggested that human Tsp cell mobilization could be manipulated as a potential cellular therapy. These data identify a distinct subset of human T cells with a quiescent/slow-cycling phenotype, propensity for tissue enrichment, and potential to mobilize into circulation, which may be harnessed for adoptive cellular therapy.

Transcription factor Nr4a1 couples sympathetic and inflammatory cues in CNS-recruited macrophages to limit neuroinflammation.

The molecular mechanisms that link the sympathetic stress response and inflammation remain obscure. Here we found that the transcription factor Nr4a1 regulated the production of norepinephrine (NE) in macrophages and thereby limited experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Lack of Nr4a1 in myeloid cells led to enhanced NE production, accelerated infiltration of leukocytes into the central nervous system (CNS) and disease exacerbation in vivo. In contrast, myeloid-specific deletion of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, protected mice against EAE. Furthermore, we found that Nr4a1 repressed autocrine NE production in macrophages by recruiting the corepressor CoREST to the Th promoter. Our data reveal a new role for macrophages in neuroinflammation and identify Nr4a1 as a key regulator of catecholamine production by macrophages.

Cutting Edge: The Orphan Nuclear Receptor Nr4a1 Regulates CD8+ T Cell Expansion and Effector Function through Direct Repression of Irf4.

The transcription factor IFN regulatory factor (IRF)4 was shown to play a crucial role in the protective CD8(+) T cell response; however, regulation of IRF4 expression in CD8(+) T cells remains unclear. In this article, we report a critical role for Nr4a1 in regulating the expansion, differentiation, and function of CD8(+) T cells through direct transcriptional repression of Irf4. Without Nr4a1, the regulation of IRF4 is lost, driving an increase in Irf4 expression and, in turn, resulting in a faster rate of CD8 T cell proliferation and expansion. Nr4a1-deficient mice show increases in CD8 T cell effector responses with improved clearance of Listeria monocytogenes. Our data support a novel and critical role for Nr4a1 in the regulation of CD8(+) T cell expansion and effector function through transcriptional repression of Irf4.

Cardif (MAVS) Regulates the Maturation of NK Cells.

Cardif, also known as IPS-1, VISA, and MAVS, is an intracellular adaptor protein that functions downstream of the retinoic acid-inducible gene I family of pattern recognition receptors. Cardif is required for the production of type I IFNs and other inflammatory cytokines after retinoic acid-inducible gene I-like receptors recognize intracellular antigenic RNA. Studies have recently shown that Cardif may have other roles in the immune system in addition to its role in viral immunity. In this study, we find that the absence of Cardif alters normal NK cell development and maturation. Cardif(-/-) mice have a 35% loss of mature CD27(-)CD11b(+) NK cells in the periphery. In addition, Cardif(-/-) NK cells have altered surface marker expression, lower cytotoxicity, decreased intracellular STAT1 levels, increased apoptosis, and decreased proliferation compared with wild-type NK cells. Mixed chimeric mice revealed that the defective maturation and increased apoptotic rate of peripheral Cardif(-/-) NK cells is cell intrinsic. However, Cardif(-/-) mice showed enhanced control of mouse CMV (a DNA ß-herpesvirus) by NK cells, commensurate with increased activation and IFN-γ production by these immature NK cell subsets. These results indicate that the skewed differentiation and altered STAT expression of Cardif(-/-) NK cells can result in their hyperresponsiveness in some settings and support recent findings that Cardif-dependent signaling can regulate aspects of immune cell development and/or function distinct from its well-characterized role in mediating cell-intrinsic defense to RNA viruses.

The nuclear receptor nr4a1 controls CD8 T cell development through transcriptional suppression of runx3.

The NR4A nuclear receptor family member Nr4a1 is strongly induced in thymocytes undergoing selection, and has been shown to control the development of Treg cells; however the role of Nr4a1 in CD8(+) T cells remains undefined. Here we report a novel role for Nr4a1 in regulating the development and frequency of CD8(+) T cells through direct transcriptional control of Runx3. We discovered that Nr4a1 recruits the corepressor, CoREST to suppress Runx3 expression in CD8(+) T cells. Loss of Nr4a1 results in increased Runx3 expression in thymocytes which consequently causes a 2-fold increase in the frequency and total number of intrathymic and peripheral CD8(+) T cells. Our findings establish Nr4a1 as a novel and critical player in the regulation of CD8 T cell development through the direct suppression of Runx3.

B cells in T follicular helper cell development and function: separable roles in delivery of ICOS ligand and antigen.

B cells are required for follicular Th (Tfh) cell development, as is the ICOS ligand (ICOS-L); however, the separable contributions of Ag and ICOS-L delivery by cognate B cells to Tfh cell development and function are unknown. We find that Tfh cell and germinal center differentiation are dependent on cognate B cell display of ICOS-L, but only when Ag presentation by the latter is limiting, with the requirement for B cell expression of ICOS-L overcome by robust Ag delivery. These findings demonstrate that Ag-specific B cells provide different, yet compensatory, signals for Tfh cell differentiation, while reconciling conflicting data indicating a requirement for ICOS-L expression on cognate B cells for Tfh cell development with those demonstrating that the latter requirement could be bypassed in lieu of that tendered by noncognate B cells. Our findings clarify the separable roles of delivery of Ag and ICOS-L by cognate B cells for Tfh cell maturation and function, and have implications for using therapeutic ICOS blockade in settings of abundantly available Ag, such as in systemic autoimmunity.

Thymic self-reactivity selects natural interleukin 17-producing T cells that can regulate peripheral inflammation.

Interleukin 17 (IL-17)-producing CD4(+) helper T cells (T(H)-17 cells) share a developmental relationship with Foxp3(+) regulatory T cells (T(reg) cells). Here we show that a T(H)-17 population differentiates in the thymus in a manner influenced by recognition of self antigen and by the cytokines IL-6 and transforming growth factor-beta (TGF-beta). Like previously described T(H)-17 cells, the T(H)-17 cells that developed in the thymus expressed the transcription factor RORgamma t and the IL-23 receptor. These cells also expressed alpha(4)beta(1) integrins and the chemokine receptor CCR6 and were recruited to the lung, gut and liver. In the liver, these cells secreted IL-22 in response to self antigen and mediated host protection during inflammation. Thus, T(H)-17 cells, like T(reg) cells, can be selected by self antigens in the thymus.