T cell response kinetics determines neuroinfection outcomes during murine HSV infection.

Herpes simplex virus-2 (HSV-2) and HSV-1 both can cause genital herpes, a chronic infection that establishes a latent reservoir in the nervous system. Clinically, the recurrence frequency of HSV-1 genital herpes is considerably less than HSV-2 genital herpes, which correlates with reduced neuronal infection. The factors dictating the disparate outcomes of HSV-1 and HSV-2 genital herpes are unclear. In this study, we show that vaginal infection of mice with HSV-1 leads to the rapid appearance of mature DCs in the draining lymph node, which is dependent on an early burst of NK cell-mediated IFN-γ production in the vagina that occurs after HSV-1 infection but not HSV-2 infection. Rapid DC maturation after HSV-1 infection, but not HSV-2 infection, correlates with the accelerated generation of a neuroprotective T cell response and early accumulation of IFN-γ-producing T cells at the site of infection. Depletion of T cells or loss of IFN-γ receptor (IFN-γR) expression in sensory neurons both lead to a marked loss of neuroprotection only during HSV-1, recapitulating a prominent feature of HSV-2 infection. Our experiments reveal key differences in host control of neuronal HSV-1 and HSV-2 infection after genital exposure of mice, and they define parameters of a successful immune response against genital herpes.

Uterine Natural Killer Cell Heterogeneity: Lessons From Mouse Models.

Natural killer (NK) cells are the most abundant lymphocytes at the maternal-fetal interface. Epidemiological data implicate NK cells in human pregnancy outcomes. Discoveries using mouse NK cells have guided subsequent advances in human NK cell biology. However, it remains challenging to identify mouse and human uterine NK (uNK) cell function(s) because of the dynamic changes in the systemic-endocrinological and local uterine structural microenvironments during pregnancy. This review discusses functional similarities and differences between mouse and human NK cells at the maternal-fetal interface.

Uterine Natural Killer Cells.

Natural killer (NK) cells are members of a rapidly expanding family of innate lymphoid cells (ILCs). While most previously studied NK cells were derived from the mouse spleen and circulate in the blood, recently others and we found tissue-resident NK (trNK) cells in many tissues that resemble group 1 ILCs (ILC1s). During pregnancy, NK cells are the most abundant lymphocytes in the uterus at the maternal-fetal interface and are involved in placental vascular remodeling. Prior studies suggested that these uterine NK (uNK) cells are mostly derived from circulating NK cells. However, the murine virgin uterus contains mostly trNK cells and it has been challenging to determine their contribution to uNK cells in pregnancy as well as other potential function(s) of uNK cells due to the dynamic microenvironment in the pregnant uterus. This review focuses on the origins and functions of the heterogeneous populations of uNK cells during the course of murine pregnancy.

Gardnerella vaginalis and Prevotella bivia Trigger Distinct and Overlapping Phenotypes in a Mouse Model of Bacterial Vaginosis.

BACKGROUND: Bacterial vaginosis (BV) is a common imbalance of the vaginal microbiota characterized by overgrowth of diverse Actinobacteria, Firmicutes, and Gram-negative anaerobes. Women with BV are at increased risk of secondary reproductive tract infections and adverse pregnancy outcomes. However, which specific bacteria cause clinical features of BV is unclear. METHODS: We previously demonstrated that Gardnerella vaginalis could elicit many BV features in mice. In this study, we established a BV model in which we coinfected mice with G. vaginalis and another species commonly found in women with BV: Prevotella bivia. RESULTS: This coinfection model recapitulates several aspects of human BV, including vaginal sialidase activity (a diagnostic BV feature independently associated with adverse outcomes), epithelial exfoliation, and ascending infection. It is notable that G. vaginalis facilitated uterine infection by P. bivia. CONCLUSIONS: Taken together, our model provides a framework for advancing our understanding of the role of individual or combinations of BV-associated bacteria in BV pathogenesis.

Viral MHCI inhibition evades tissue-resident memory T cell formation and responses.

Tissue-resident memory CD8+ T cells (TRMs) confer rapid protection and immunity against viral infections. Many viruses have evolved mechanisms to inhibit MHCI presentation in order to evade CD8+ T cells, suggesting that these mechanisms may also apply to TRM-mediated protection. However, the effects of viral MHCI inhibition on the function and generation of TRMs is unclear. Herein, we demonstrate that viral MHCI inhibition reduces the abundance of CD4+ and CD8+ TRMs, but its effects on the local microenvironment compensate to promote antigen-specific CD8+ TRM formation. Unexpectedly, local cognate antigen enhances CD8+ TRM development even in the context of viral MHCI inhibition and CD8+ T cell evasion, strongly suggesting a role for in situ cross-presentation in local antigen-driven TRM differentiation. However, local cognate antigen is not required for CD8+ TRM maintenance. We also show that viral MHCI inhibition efficiently evades CD8+ TRM effector functions. These findings indicate that viral evasion of MHCI antigen presentation has consequences on the development and response of antiviral TRMs.

Uterine natural killer cells: To protect and to nurture.

During the course of pregnancy, the maternal-fetal interface is tightly regulated and undergoes dynamic changes that promote the successful development of the semi-allogeneic fetus. In response to embryo implantation, the uterus remodels with maternal immune cells occupying the maternal-fetal interface and uterine natural killer (uNK) cells becoming the most prominent leukocyte. Recently, uNK cells have been discovered to be heterogeneous, including conventional NK and tissue-resident NK cells. Here, we will review the recent advances in uNK cell biology and discuss their functional mechanisms which protect and nurture the growing fetus.

Cutting Edge: Local Proliferation of Uterine Tissue-Resident NK Cells during Decidualization in Mice.

NK cells accumulate in adult murine and human uteri during decidualization induced physiologically, pathologically, or experimentally. Adoptive transfer studies indicate that uterine NK (uNK) cells arise from circulating progenitors. However, virgin uteri contain few circulating NK1.1+CD49a- conventional NK cells, whereas NK1.1+CD49a+ tissue-resident NK (trNK) cells are abundant. In this study, we employed a novel, immune-competent NK cell-specific reporter mouse to track accumulation of uNK cells during unmanipulated pregnancies. We identified conventional NK and trNK cells accumulating in both decidua basalis and myometrium. Only trNK cells showed evidence of proliferation. In parabiosis studies using experimentally induced deciduomata, the accumulated uNK cells were proliferating trNK cells; migrating NK cells made no contribution. Together, these data suggest proliferating trNK cells are the source of uNK cells during endometrial decidualization.

Mouse models of preterm birth: suggested assessment and reporting guidelines.

Preterm birth affects approximately 1 out of every 10 births in the United States, leading to high rates of mortality and long-term negative health consequences. To investigate the mechanisms leading to preterm birth so as to develop prevention strategies, researchers have developed numerous mouse models of preterm birth. However, the lack of standard definitions for preterm birth in mice limits our field's ability to compare models and make inferences about preterm birth in humans. In this review, we discuss numerous mouse preterm birth models, propose guidelines for experiments and reporting, and suggest markers that can be used to assess whether pups are premature or mature. We argue that adoption of these recommendations will enhance the utility of mice as models for preterm birth.

Tissue-Resident Macrophages in Pancreatic Ductal Adenocarcinoma Originate from Embryonic Hematopoiesis and Promote Tumor Progression.

Tumor-associated macrophages (TAMs) are essential components of the cancer microenvironment and play critical roles in the regulation of tumor progression. Optimal therapeutic intervention requires in-depth understanding of the sources that sustain macrophages in malignant tissues. In this study, we investigated the ontogeny of TAMs in murine pancreatic ductal adenocarcinoma (PDAC) models. We identified both inflammatory monocytes and tissue-resident macrophages as sources of TAMs. Unexpectedly, significant portions of pancreas-resident macrophages originated from embryonic development and expanded through in situ proliferation during tumor progression. Whereas monocyte-derived TAMs played more potent roles in antigen presentation, embryonically derived TAMs exhibited a pro-fibrotic transcriptional profile, indicative of their role in producing and remodeling molecules in the extracellular matrix. Collectively, these findings uncover the heterogeneity of TAM origin and functions and could provide therapeutic insight for PDAC treatment.

Tissue-Resident NK Cells Mediate Ischemic Kidney Injury and Are Not Depleted by Anti-Asialo-GM1 Antibody.

NK cells are innate lymphoid cells important for immune surveillance, identifying and responding to stress, infection, and/or transformation. Whereas conventional NK (cNK) cells circulate systemically, many NK cells reside in tissues where they appear to be poised to locally regulate tissue function. In the present study, we tested the contribution of tissue-resident NK (trNK) cells to tissue homeostasis by studying ischemic injury in the mouse kidney. Parabiosis experiments demonstrate that the kidney contains a significant fraction of trNK cells under homeostatic conditions. Kidney trNK cells developed independent of NFIL3 and T-bet, and they expressed a distinct cell surface phenotype as compared with cNK cells. Among these, trNK cells had reduced asialo-GM1 (AsGM1) expression relative to cNK cells, a phenotype observed in trNK cells across multiple organs and mouse strains. Strikingly, anti-AsGM1 Ab treatment, commonly used as an NK cell-depleting regimen, resulted in a robust and selective depletion of cNKs, leaving trNKs largely intact. Using this differential depletion, we tested the relative contribution of cNK and trNK cells in ischemic kidney injury. Whereas anti-NK1.1 Ab effectively depleted both trNK and cNK cells and protected against ischemic/reperfusion injury, anti-AsGM1 Ab preferentially depleted cNK cells and failed to protect against injury. These data demonstrate unanticipated specificity of anti-AsGM1 Ab depletion on NK cell subsets and reveal a new approach to study the contributions of cNK and trNK cells in vivo. In total, these data demonstrate that trNK cells play a key role in modulating local responses to ischemic tissue injury in the kidney and potentially other organs.

The pancreas anatomy conditions the origin and properties of resident macrophages.

We examine the features, origin, turnover, and gene expression of pancreatic macrophages under steady state. The data distinguish macrophages within distinct intrapancreatic microenvironments and suggest how macrophage phenotype is imprinted by the local milieu. Macrophages in islets of Langerhans and in the interacinar stroma are distinct in origin and phenotypic properties. In islets, macrophages are the only myeloid cells: they derive from definitive hematopoiesis, exchange to a minimum with blood cells, have a low level of self-replication, and depend on CSF-1. They express Il1b and Tnfa transcripts, indicating classical activation, M1, under steady state. The interacinar stroma contains two macrophage subsets. One is derived from primitive hematopoiesis, with no interchange by blood cells and alternative, M2, activation profile, whereas the second is derived from definitive hematopoiesis and exchanges with circulating myeloid cells but also shows an alternative activation profile. Complete replacement of islet and stromal macrophages by donor stem cells occurred after lethal irradiation with identical profiles as observed under steady state. The extraordinary plasticity of macrophages within the pancreatic organ and the distinct features imprinted by their anatomical localization sets the base for examining these cells in pathological conditions.

Tissue-resident natural killer (NK) cells are cell lineages distinct from thymic and conventional splenic NK cells.

Natural killer (NK) cells belong to the innate immune system; they can control virus infections and developing tumors by cytotoxicity and producing inflammatory cytokines. Most studies of mouse NK cells, however, have focused on conventional NK (cNK) cells in the spleen. Recently, we described two populations of liver NK cells, tissue-resident NK (trNK) cells and those resembling splenic cNK cells. However, their lineage relationship was unclear; trNK cells could be developing cNK cells, related to thymic NK cells, or a lineage distinct from both cNK and thymic NK cells. Herein we used detailed transcriptomic, flow cytometric, and functional analysis and transcription factor-deficient mice to determine that liver trNK cells form a distinct lineage from cNK and thymic NK cells. Taken together with analysis of trNK cells in other tissues, there are at least four distinct lineages of NK cells: cNK, thymic, liver (and skin) trNK, and uterine trNK cells. DOI: http://dx.doi.org/10.7554/eLife.01659.001.

Tissue-resident natural killer cells and their potential diversity.

Conventional NK cells are well characterized in the mouse spleen and circulate in the blood. Less well described are NK cells found in organs such as the liver, thymus, and uterus. Recently we identified a tissue-resident NK (trNK) cell population in the liver, suggesting a potential diversity of trNK cells in other organs. In this review we compare and contrast the similarities and differences among the subpopulations of NK and innate lymphoid cells to the trNK cells in the liver.

Embryonic and adult-derived resident cardiac macrophages are maintained through distinct mechanisms at steady state and during inflammation.

Cardiac macrophages are crucial for tissue repair after cardiac injury but are not well characterized. Here we identify four populations of cardiac macrophages. At steady state, resident macrophages were primarily maintained through local proliferation. However, after macrophage depletion or during cardiac inflammation, Ly6c(hi) monocytes contributed to all four macrophage populations, whereas resident macrophages also expanded numerically through proliferation. Genetic fate mapping revealed that yolk-sac and fetal monocyte progenitors gave rise to the majority of cardiac macrophages, and the heart was among a minority of organs in which substantial numbers of yolk-sac macrophages persisted in adulthood. CCR2 expression and dependence distinguished cardiac macrophages of adult monocyte versus embryonic origin. Transcriptional and functional data revealed that monocyte-derived macrophages coordinate cardiac inflammation, while playing redundant but lesser roles in antigen sampling and efferocytosis. These data highlight the presence of multiple cardiac macrophage subsets, with different functions, origins, and strategies to regulate compartment size.

Minimal differentiation of classical monocytes as they survey steady-state tissues and transport antigen to lymph nodes.

It is thought that monocytes rapidly differentiate to macrophages or dendritic cells (DCs) upon leaving blood. Here we have shown that Ly-6C⁺ monocytes constitutively trafficked into skin, lung, and lymph nodes (LNs). Entry was unaffected in gnotobiotic mice. Monocytes in resting lung and LN had similar gene expression profiles to blood monocytes but elevated transcripts of a limited number of genes including cyclo-oxygenase-2 (COX-2) and major histocompatibility complex class II (MHCII), induced by monocyte interaction with endothelium. Parabiosis, bromodoxyuridine (BrdU) pulse-chase analysis, and intranasal instillation of tracers indicated that instead of contributing to resident macrophages in the lung, recruited endogenous monocytes acquired antigen for carriage to draining LNs, a function redundant with DCs though differentiation to DCs did not occur. Thus, monocytes can enter steady-state nonlymphoid organs and recirculate to LNs without differentiation to macrophages or DCs, revising a long-held view that monocytes become tissue-resident macrophages by default.

Liver-resident NK cells confer adaptive immunity in skin-contact inflammation.

Liver natural killer (NK) cells were recently reported to possess memory-like properties in contact hypersensitivity (CHS) models. However, the phenotype and origin of these "memory" NK cells cannot be distinguished from other NK cell subpopulations. Here, we define the transcriptional, phenotypic, and functional features of liver NK cell subsets and their roles in mediating CHS. Liver NK cells can be divided into two distinct subsets: CD49a+DX5- and CD49a-DX5+. Substantial transcriptional and phenotypic differences existed between liver CD49a+DX5- NK cells and other NK cell subsets. CD49a+DX5- NK cells possessed memory potential and conferred hapten-specific CHS responses upon hapten challenge. Importantly, CD49a+DX5- NK cells were liver resident and were present in the liver sinusoidal blood, but not the afferent and efferent blood of the liver. Moreover, they appeared to originate from hepatic hematopoietic progenitor/stem cells (HPCs/HSCs) but not from the bone marrow, and maintained their phenotypes in the steady state. Our findings of liver-resident NK cells shed new light on the acquisition of memory-like properties of NK cells.

Interferon-γ mediates chemokine-dependent recruitment of natural killer cells during viral infection.

Natural killer (NK) cells provide in vivo control of orthopoxvirus infections in association with their expansion in the draining lymph node (LN), where they are normally very rare. The mechanism of this expansion is unclear. Herein, we determined that NK-cell depletion results in enhanced infection following footpad inoculation of cowpox virus, a natural pathogen of rodents. Following cowpox virus infection in normal mice, NK cells were greatly expanded in the draining LN, were not replicating, and displayed markers similar to splenic NK cells, suggesting specific recruitment of splenic NK cells rather than in situ proliferation. Moreover, NK-cell expansion was abrogated by prior injection of clodronate-loaded liposomes, indicating a role for subcapsular sinus macrophages. Furthermore, recruitment of transferred splenic NK cells to the draining LN was pertussis toxin-sensitive, suggesting involvement of chemokine receptors. Comprehensive analysis of chemokine mRNA expression in the draining LN following infection suggested the selective involvement of CCR2, CCR5, and/or CXCR3. Mice deficient for CCR2 or CCR5 had normal NK-cell recruitment, whereas CXCR3-deficient mice displayed a major defect, which was NK cell-intrinsic. Interestingly, both induction of transcripts for CXCR3 ligands (Cxcl9 and Cxcl10) and NK-cell recruitment required IFN-γ. These data indicate that NK-cell recruitment is mediated by subcapsular sinus macrophages, IFN-γ, and CXCR3 during orthopoxvirus infection.

Tissue-resident natural killer cells.

Natural killer (NK) cells kill infected and tumor cells and produce cytokines that modulate other immune cells. However, most of our current knowledge is derived from investigations of mouse splenic and human peripheral blood NK cells, "conventional" NK cells. Herein we discuss recent studies indicating that the liver contains two subpopulations of NK cells, one of which is liver-resident and bears distinct markers from another liver subpopulation that resembles conventional NK cells. Thus, the liver and potentially other organs contain tissue-resident NK cells that may differ from conventional NK cells in terms of origin, development, and/or function.

Cutting edge: Regulatory T cells selectively attenuate, not terminate, T cell signaling by disrupting NF-κB nuclear accumulation in CD4 T cells.

A key consequence of regulatory T cell (Treg) suppression of CD4 T cells is the inhibition of IL-2 production, yet how Tregs attenuate IL-2 has not been defined. Current models predict a termination of TCR signaling, by disrupting T-APC contacts, or TCR signal modification, through mechanisms such as cAMP. To directly define Treg effects on TCR signaling in CD4 T cell targets, we visualized changes in nuclear accumulation of transcription factors at time points when IL-2 was actively suppressed. Nuclear accumulation of NFAT was highly dependent on sustained TCR signaling in the targets. However, in the presence of Tregs, NFAT and AP-1 signals were sustained in the target cells. In contrast, NF-κB p65 was selectively attenuated. Thus, Tregs do not generally terminate TCR signals. Rather, Tregs selectively modulate TCR signals within hours of contact with CD4 targets, independent of APCs, resulting in the specific loss of NF-κB p65 signals.