Dysregulated lung stroma drives emphysema exacerbation by potentiating resident lymphocytes to suppress an epithelial stem cell reservoir.

Aberrant tissue-immune interactions are the hallmark of diverse chronic lung diseases. Here, we sought to define these interactions in emphysema, a progressive disease characterized by infectious exacerbations and loss of alveolar epithelium. Single-cell analysis of human emphysema lungs revealed the expansion of tissue-resident lymphocytes (TRLs). Murine studies identified a stromal niche for TRLs that expresses Hhip, a disease-variant gene downregulated in emphysema. Stromal-specific deletion of Hhip induced the topographic expansion of TRLs in the lung that was mediated by a hyperactive hedgehog-IL-7 axis. 3D immune-stem cell organoids and animal models of viral exacerbations demonstrated that expanded TRLs suppressed alveolar stem cell growth through interferon gamma (IFNγ). Finally, we uncovered an IFNγ-sensitive subset of human alveolar stem cells that was preferentially lost in emphysema. Thus, we delineate a stromal-lymphocyte-epithelial stem cell axis in the lung that is modified by a disease-variant gene and confers host susceptibility to emphysema.

Interferon gamma constrains type 2 lymphocyte niche boundaries during mixed inflammation.

Allergic immunity is orchestrated by group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells prominently arrayed at epithelial- and microbial-rich barriers. However, ILC2s and Th2 cells are also present in fibroblast-rich niches within the adventitial layer of larger vessels and similar boundary structures in sterile deep tissues, and it remains unclear whether they undergo dynamic repositioning during immune perturbations. Here, we used thick-section quantitative imaging to show that allergic inflammation drives invasion of lung and liver non-adventitial parenchyma by ILC2s and Th2 cells. However, during concurrent type 1 and type 2 mixed inflammation, IFNγ from broadly distributed type 1 lymphocytes directly blocked both ILC2 parenchymal trafficking and subsequent cell survival. ILC2 and Th2 cell confinement to adventitia limited mortality by the type 1 pathogen Listeria monocytogenes. Our results suggest that the topography of tissue lymphocyte subsets is tightly regulated to promote appropriately timed and balanced immunity.

Adventitial Stromal Cells Define Group 2 Innate Lymphoid Cell Tissue Niches.

Type 2 lymphocytes promote both physiologic tissue remodeling and allergic pathology, yet their physical tissue niches are poorly described. Here, we used quantitative imaging to define the tissue niches of group 2 innate lymphoid cells (ILC2s), which are critical instigators of type 2 immunity. We identified a dominant adventitial niche around lung bronchi and larger vessels in multiple tissues, where ILC2s localized with subsets of dendritic and regulatory T cells. However, ILC2s were most intimately associated with adventitial stromal cells (ASCs), a mesenchymal fibroblast-like subset that expresses interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP). In vitro, ASCs produced TSLP that supported ILC2 accumulation and activation. ILC2s and IL-13 drove reciprocal ASC expansion and IL-33 expression. During helminth infection, ASC depletion impaired lung ILC2 and Th2 cell accumulation and function, which are in part dependent on ASC-derived IL-33. These data indicate that adventitial niches are conserved sites where ASCs regulate type 2 lymphocyte expansion and function.

Adventitial Cuffs: Regional Hubs for Tissue Immunity.

Inflammation must be effective, while limiting excessive tissue damage. To walk this line, immune functions are grossly compartmentalized by innate cells that act locally and adaptive cells that function systemically. But what about the myriad tissue-resident immune cells that are critical to this balancing act and lie on a spectrum of innate and adaptive immunity? We propose that mammalian perivascular adventitial 'cuffs' are conserved sites in multiple organs, enriched for these tissue-resident lymphocytes and dendritic cells, as well as lymphatics, nerves, and subsets of specialized stromal cells. Here, we argue that these boundary sites integrate diverse tissue signals to regulate the movement of immune cells and interstitial fluid, facilitate immune crosstalk, and ultimately act to coordinate regional tissue immunity.

Extracellular Histones Induce Chemokine Production in Whole Blood Ex Vivo and Leukocyte Recruitment In Vivo.

The innate immune system relies to a great deal on the interaction of pattern recognition receptors with pathogen- or damage-associated molecular pattern molecules. Extracellular histones belong to the latter group and their release has been described to contribute to the induction of systemic inflammatory reactions. However, little is known about their functions in the early immune response to an invading pathogen. Here we show that extracellular histones specifically target monocytes in human blood and this evokes the mobilization of the chemotactic chemokines CXCL9 and CXCL10 from these cells. The chemokine induction involves the toll-like receptor 4/myeloid differentiation factor 2 complex on monocytes, and is under the control of interferon-γ. Consequently, subcutaneous challenge with extracellular histones results in elevated levels of CXCL10 in a murine air pouch model and an influx of leukocytes to the site of injection in a TLR4 dependent manner. When analyzing tissue biopsies from patients with necrotizing fasciitis caused by Streptococcus pyogenes, extracellular histone H4 and CXCL10 are immunostained in necrotic, but not healthy tissue. Collectively, these results show for the first time that extracellular histones have an important function as chemoattractants as their local release triggers the recruitment of immune cells to the site of infection.

T follicular helper, but not Th1, cell differentiation in the absence of conventional dendritic cells.

Development of long-lived humoral immunity is dependent on CXCR5-expressing T follicular helper (Tfh) cells, which develop concomitantly to effector Th cells that support cellular immunity. Conventional dendritic cells (cDCs) are critical APCs for initial priming of naive CD4(+) T cells but, importantly, also provide accessory signals that govern effector Th cell commitment. To define the accessory role of cDCs during the concurrent development of Tfh and effector Th1 cells, we performed high-dose Ag immunization in conjunction with the Th1-biased adjuvant polyinosinic:polycytidylic acid (pI:C). In the absence of cDCs, pI:C failed to induce Th1 cell commitment and IgG2c production. However, cDC depletion did not impair Tfh cell differentiation or germinal center formation, and long-lived IgG1 responses of unaltered affinity developed in mice lacking cDCs at the time point for immunization. Thus, cDCs are required for the pI:C-driven Th1 cell fate commitment but have no crucial accessory function in relation to Tfh cell differentiation.

Direct interaction between cholera toxin and dendritic cells is required for oral adjuvant activity.

Cholera toxin (CT) binds to GM1-ganglioside receptors present on all nucleated cells. Despite this, it is a very potent mucosal adjuvant that has a dramatic impact on immune cells, as well as nerve and epithelial cells, causing diarrhea. This fact has hampered our understanding of whether the adjuvanticity of CT is direct or indirect, as cells that bind CT may or may not be involved in its adjuvant function. The mucosal barrier is maintained by tight junctions between epithelial cells but dendritic cells (DCs) can protrude luminal dendrites. Here we investigated which cells are involved in the immune augmenting effect of CT. We explored oral immunizations with ovalbumin (OVA) and CT in bone marrow chimeric mice deficient in GM1-ganglioside in defined cellular subsets. We found that chimeric mice lacking GM1 in nonhematopoietic cells, including epithelial cells, mounted an unaltered intestinal IgA response. In contrast, chimeric mice lacking GM1-expressing hematopoietic cells in general, or specifically GM1-expressing conventional DCs (cDCs), largely failed to elicit anti-OVA adaptive immune responses. Therefore, the adjuvanticity of CT does not require epithelial activation, but is directly dependent on the binding of CT to gut cDCs via GM1-ganglioside. These results could have important implications for the generation of novel oral adjuvants.

Group 2 innate lymphoid cells promote inhibitory synapse development and social behavior.

The innate immune system plays essential roles in brain synaptic development, and immune dysregulation is implicated in neurodevelopmental diseases. Here we show that a subset of innate lymphocytes (group 2 innate lymphoid cells, ILC2s) is required for cortical inhibitory synapse maturation and adult social behavior. ILC2s expanded in the developing meninges and produced a surge of their canonical cytokine Interleukin-13 (IL-13) between postnatal days 5-15. Loss of ILC2s decreased cortical inhibitory synapse numbers in the postnatal period where as ILC2 transplant was sufficient to increase inhibitory synapse numbers. Deletion of the IL-4/IL-13 receptor (Il4ra) from inhibitory neurons phenocopied the reduction inhibitory synapses. Both ILC2 deficient and neuronal Il4ra deficient animals had similar and selective impairments in adult social behavior. These data define a type 2 immune circuit in early life that shapes adult brain function.

Group 2 innate lymphoid cells constrain type 3/17 lymphocytes in shared stromal niches to restrict liver fibrosis.

Group 2 innate lymphoid cells (ILC2s) cooperate with adaptive Th2 cells as key organizers of tissue type 2 immune responses, while a spectrum of innate and adaptive lymphocytes coordinate early type 3/17 immunity. Both type 2 and type 3/17 lymphocyte associated cytokines are linked to tissue fibrosis, but how their dynamic and spatial topographies may direct beneficial or pathologic organ remodelling is unclear. Here we used volumetric imaging in models of liver fibrosis, finding accumulation of periportal and fibrotic tract IL-5 + lymphocytes, predominantly ILC2s, in close proximity to expanded type 3/17 lymphocytes and IL-33 high niche fibroblasts. Ablation of IL-5 + lymphocytes worsened carbon tetrachloride-and bile duct ligation-induced liver fibrosis with increased niche IL-17A + type 3/17 lymphocytes, predominantly γδ T cells. In contrast, concurrent ablation of IL-5 + and IL-17A + lymphocytes reduced this progressive liver fibrosis, suggesting a cross-regulation of type 2 and type 3 lymphocytes at specialized fibroblast niches that tunes hepatic fibrosis.

Type I Interferons Promote Germinal Centers Through B Cell Intrinsic Signaling and Dendritic Cell Dependent Th1 and Tfh Cell Lineages.

Type I interferons (IFNs) are essential for antiviral immunity, appear to represent a key component of mRNA vaccine-adjuvanticity, and correlate with severity of systemic autoimmune disease. Relevant to all, type I IFNs can enhance germinal center (GC) B cell responses but underlying signaling pathways are incompletely understood. Here, we demonstrate that a succinct type I IFN response promotes GC formation and associated IgG subclass distribution primarily through signaling in cDCs and B cells. Type I IFN signaling in cDCs, distinct from cDC1, stimulates development of separable Tfh and Th1 cell subsets. However, Th cell-derived IFN-γ induces T-bet expression and IgG2c isotype switching in B cells prior to this bifurcation and has no evident effects once GCs and bona fide Tfh cells developed. This pathway acts in synergy with early B cell-intrinsic type I IFN signaling, which reinforces T-bet expression in B cells and leads to a selective amplification of the IgG2c+ GC B cell response. Despite the strong Th1 polarizing effect of type I IFNs, the Tfh cell subset develops into IL-4 producing cells that control the overall magnitude of the GCs and promote generation of IgG1+ GC B cells. Thus, type I IFNs act on B cells and cDCs to drive GC formation and to coordinate IgG subclass distribution through divergent Th1 and Tfh cell-dependent pathways.

Regulatory T-cells inhibit microglia-induced pain hypersensitivity in female mice.

Peripheral nerve injury-induced neuropathic pain is a chronic and debilitating condition characterized by mechanical hypersensitivity. We previously identified microglial activation via release of colony-stimulating factor 1 (CSF1) from injured sensory neurons as a mechanism contributing to nerve injury-induced pain. Here, we show that intrathecal administration of CSF1, even in the absence of injury, is sufficient to induce pain behavior, but only in male mice. Transcriptional profiling and morphologic analyses after intrathecal CSF1 showed robust immune activation in male but not female microglia. CSF1 also induced marked expansion of lymphocytes within the spinal cord meninges, with preferential expansion of regulatory T-cells (Tregs) in female mice. Consistent with the hypothesis that Tregs actively suppress microglial activation in females, Treg deficient (Foxp3DTR) female mice showed increased CSF1-induced microglial activation and pain hypersensitivity equivalent to males. We conclude that sexual dimorphism in the contribution of microglia to pain results from Treg-mediated suppression of microglial activation and pain hypersensitivity in female mice.

All along the watchtower: group 2 innate lymphoid cells in allergic responses.

Group 2 innate lymphoid cells (ILC2) are a subset of innate lymphocytes that responds to local, tissue-derived signals and initiates allergic immune responses. ILC2 activation promotes the recruitment of eosinophils, polarization of alternatively activated macrophages, and tissue-remodeling, processes associated with the 'weep and sweep' response to helminthic worm colonization and infection. ILC2s also coordinate both physiologic and pathologic type 2 allergic immune responses, including promoting normal tissue development and remodeling and driving allergic pathology such as atopic dermatitis and allergic asthma. In this review we summarize recent advances in ILC2 biology, particularly focusing on how local cells and signals coordinately regulate ILC2s, how this may influence physiologic processes, and how ILC2 cooperate with adaptive T helper type 2 cells to drive pathologic allergic inflammation.

Intestinal CD103+CD11b+ cDC2 Conventional Dendritic Cells Are Required for Primary CD4+ T and B Cell Responses to Soluble Flagellin.

Systemic immunization with soluble flagellin (sFliC) from Salmonella Typhimurium induces mucosal responses, offering potential as an adjuvant platform for vaccines. Moreover, this engagement of mucosal immunity is necessary for optimal systemic immunity, demonstrating an interaction between these two semi-autonomous immune systems. Although TLR5 and CD103+CD11b+ cDC2 contribute to this process, the relationship between these is unclear in the early activation of CD4+ T cells and the development of antigen-specific B cell responses. In this work, we use TLR5-deficient mice and CD11c-cre.Irf4fl/fl mice (which have reduced numbers of cDC2, particularly intestinal CD103+CD11b+ cDCs), to address these points by studying the responses concurrently in the spleen and the mesenteric lymph nodes (MLN). We show that CD103+CD11b+ cDC2 respond rapidly and accumulate in the MLN after immunization with sFliC in a TLR5-dependent manner. Furthermore, we identify that whilst CD103+CD11b+ cDC2 are essential for the induction of primary T and B cell responses in the mucosa, they do not play such a central role for the induction of these responses in the spleen. Additionally, we show the involvement of CD103+CD11b+ cDC2 in the induction of Th2-associated responses. CD11c-cre.Irf4fl/fl mice showed a reduced primary FliC-specific Th2-associated IgG1 responses, but enhanced Th1-associated IgG2c responses. These data expand our current understanding of the mucosal immune responses promoted by sFliC and highlights the potential of this adjuvant for vaccine usage by taking advantage of the functionality of mucosal CD103+CD11b+ cDC2.