Vitamin D regulates microbiome-dependent cancer immunity.

A role for vitamin D in immune modulation and in cancer has been suggested. In this work, we report that mice with increased availability of vitamin D display greater immune-dependent resistance to transplantable cancers and augmented responses to checkpoint blockade immunotherapies. Similarly, in humans, vitamin D-induced genes correlate with improved responses to immune checkpoint inhibitor treatment as well as with immunity to cancer and increased overall survival. In mice, resistance is attributable to the activity of vitamin D on intestinal epithelial cells, which alters microbiome composition in favor of Bacteroides fragilis, which positively regulates cancer immunity. Our findings indicate a previously unappreciated connection between vitamin D, microbial commensal communities, and immune responses to cancer. Collectively, they highlight vitamin D levels as a potential determinant of cancer immunity and immunotherapy success.

Interplay between CXCR4 and CCR2 regulates bone marrow exit of dendritic cell progenitors.

Conventional dendritic cells (cDCs) are found in most tissues and play a key role in initiation of immunity. cDCs require constant replenishment from progenitors called pre-cDCs that develop in the bone marrow (BM) and enter the blood circulation to seed all tissues. This process can be markedly accelerated in response to inflammation (emergency cDCpoiesis). Here, we identify two populations of BM pre-cDC marked by differential expression of CXCR4. We show that CXCR4lo cells constitute the migratory pool of BM pre-cDCs, which exits the BM and can be rapidly mobilized during challenge. We further show that exit of CXCR4lo pre-cDCs from BM at steady state is partially dependent on CCR2 and that CCR2 upregulation in response to type I IFN receptor signaling markedly increases efflux during infection with influenza A virus. Our results highlight a fine balance between retention and efflux chemokine cues that regulates steady-state and emergency cDCpoiesis.

Loss of TET2 in human hematopoietic stem cells alters the development and function of neutrophils.

Somatic mutations commonly occur in hematopoietic stem cells (HSCs). Some mutant clones outgrow through clonal hematopoiesis (CH) and produce mutated immune progenies shaping host immunity. Individuals with CH are asymptomatic but have an increased risk of developing leukemia, cardiovascular and pulmonary inflammatory diseases, and severe infections. Using genetic engineering of human HSCs (hHSCs) and transplantation in immunodeficient mice, we describe how a commonly mutated gene in CH, TET2, affects human neutrophil development and function. TET2 loss in hHSCs produce a distinct neutrophil heterogeneity in bone marrow and peripheral tissues by increasing the repopulating capacity of neutrophil progenitors and giving rise to low-granule neutrophils. Human neutrophils that inherited TET2 mutations mount exacerbated inflammatory responses and have more condensed chromatin, which correlates with compact neutrophil extracellular trap (NET) production. We expose here physiological abnormalities that may inform future strategies to detect TET2-CH and prevent NET-mediated pathologies associated with CH.

Signaling Pathways That Mediate Alveolar Macrophage Activation by Surfactant Protein A and IL-4.

Activation of tissue repair program in macrophages requires the integration of IL-4/IL-13 cytokines and tissue-specific signals. In the lung, surfactant protein A (SP-A) is a tissue factor that amplifies IL-4Rα-dependent alternative activation and proliferation of alveolar macrophages (AMs) through the myosin18A receptor. However, the mechanism by which SP-A and IL-4 synergistically increase activation and proliferation of AMs is unknown. Here we show that SP-A amplifies IL-4-mediated phosphorylation of STAT6 and Akt by binding to myosin18A. Blocking PI3K activity or the myosin18A receptor abrogates SP-A´s amplifying effects on IL-4 signaling. SP-A alone activates Akt, mTORC1, and PKCζ and inactivates GSK3α/ß by phosphorylation, but it cannot activate arginase-1 activity or AM proliferation on its own. The combined effects of IL-4 and SP-A on the mTORC1 and GSK3 branches of PI3K-Akt signaling contribute to increased AM proliferation and alternative activation, as revealed by pharmacological inhibition of Akt (inhibitor VIII) and mTORC1 (rapamycin and torin). On the other hand, the IL-4+SP-A-driven PKCζ signaling axis appears to intersect PI3K activation with STAT6 phosphorylation to achieve more efficient alternative activation of AMs. Consistent with IL-4+SP-A-driven activation of mTORC1 and mTORC2, both agonists synergistically increased mitochondrial respiration and glycolysis in AMs, which are necessary for production of energy and metabolic intermediates for proliferation and alternative activation. We conclude that SP-A signaling in AMs activates PI3K-dependent branched pathways that amplify IL-4 actions on cell proliferation and the acquisition of AM effector functions.

Dendritic Cells Revisited.

Dendritic cells (DCs) possess the ability to integrate information about their environment and communicate it to other leukocytes, shaping adaptive and innate immunity. Over the years, a variety of cell types have been called DCs on the basis of phenotypic and functional attributes. Here, we refocus attention on conventional DCs (cDCs), a discrete cell lineage by ontogenetic and gene expression criteria that best corresponds to the cells originally described in the 1970s. We summarize current knowledge of mouse and human cDC subsets and describe their hematopoietic development and their phenotypic and functional attributes. We hope that our effort to review the basic features of cDC biology and distinguish cDCs from related cell types brings to the fore the remarkable properties of this cell type while shedding some light on the seemingly inordinate complexity of the DC field.

Soluble defense collagens: Sweeping up immune threats.

Soluble defense collagens form a group of secreted proteins that are primarily involved in host defense. All defense collagens contain a globular recognition domain contiguous to a collagen-like triple helical domain. They are oligomeric proteins, assembled in multiples of three subunits due to their collagen domains. Members of this group include collectins such as surfactant protein A and D (SP-A, SP-D), and mannan-binding lectin; C1q, the first component of the complement system; adiponectin; and ficolins. All are secreted to tissue cavities or serum. Soluble defense collagens are specialized to respond to infection, triggering the initiation of the complement cascade and/or enhancing phagocytosis of pathogens by macrophages. However, once inflammation is established, C1q, collectins, ficolins, or adiponectin can influence macrophage responses, thereby contributing to resolve the inflammation. In addition, some members of this group of proteins (SP-A, C1q, and adiponectin) modulate tissue-repair functions of macrophages. This review will focus on the molecular mechanisms by which these proteins efficiently defend against immune threats and contribute to tissue repair.

Lung Surfactant Lipids Provide Immune Protection Against Haemophilus influenzae Respiratory Infection.

Non-typeable Haemophilus influenzae (NTHi) causes persistent respiratory infections in patients with chronic obstructive pulmonary disease (COPD), probably linked to its capacity to invade and reside within pneumocytes. In the alveolar fluid, NTHi is in contact with pulmonary surfactant, a lipoprotein complex that protects the lung against alveolar collapse and constitutes the front line of defense against inhaled pathogens and toxins. Decreased levels of surfactant phospholipids have been reported in smokers and patients with COPD. The objective of this study was to investigate the effect of surfactant phospholipids on the host-pathogen interaction between NTHi and pneumocytes. For this purpose, we used two types of surfactant lipid vesicles present in the alveolar fluid: (i) multilamellar vesicles (MLVs, > 1 µm diameter), which constitute the tensioactive material of surfactant, and (ii) small unilamellar vesicles (SUVs, 0.1 µm diameter), which are generated after inspiration/expiration cycles, and are endocytosed by pneumocytes for their degradation and/or recycling. Results indicated that extracellular pulmonary surfactant binds to NTHi, preventing NTHi self-aggregation and inhibiting adhesion of NTHi to pneumocytes and, consequently, inhibiting NTHi invasion. In contrast, endocytosed surfactant lipids, mainly via the scavenger receptor SR-BI, did not affect NTHi adhesion but inhibited NTHi invasion by blocking bacterial uptake in pneumocytes. This blockade was made possible by inhibiting Akt phosphorylation and Rac1 GTPase activation, which are signaling pathways involved in NTHi internalization. Administration of the hydrophobic fraction of lung surfactant in vivo accelerated bacterial clearance in a mouse model of NTHi pulmonary infection, supporting the notion that the lipid component of lung surfactant protects against NTHi infection. These results suggest that alterations in surfactant lipid levels in COPD patients may increase susceptibility to infection by this pathogen.

Immune- and non-immune-mediated roles of regulatory T-cells during wound healing.

The immune system has a well-established contribution to tissue homeostasis and wound healing. However, in many cases immune responses themselves can cause severe tissue damage. Thus, the question arose to which extent cells of the immune system directly contribute to the process of wound healing and to which extent the resolution of excessive immune responses may indirectly contribute to wound healing. FoxP3-expressing CD4 T-cells, so-called regulatory T-cells (Tregs ), have an important contribution in the regulation of immune responses; and, in recent years, it has been suggested that Tregs next to an immune-regulatory, 'damage-limiting' function may also have an immune-independent 'damage-resolving' direct role in wound healing. In particular, the release of the epidermal growth factor-like growth factor Amphiregulin by tissue-resident Tregs during wound repair suggested such a function. Our recent findings have now revealed that Amphiregulin induces the local release of bio-active transforming growth factor (TGF)ß, a cytokine involved both in immune regulation as well as in the process of wound repair. In light of these findings, we discuss whether, by locally activating TGFß, Treg -derived Amphiregulin may contribute to both wound repair and immune suppression. Furthermore, we propose that Treg -derived Amphiregulin in an autocrine way may enable an IL-33-mediated survival and expansion of tissue-resident Tregs upon injury. Furthermore, Treg -derived Amphiregulin may contribute to a constitutive, low-level release of bio-active TGFß within tissues, leading to continuous tissue regeneration and to an immune-suppressive environment, which may keep inflammation-prone tissues in an homeostatic state.

A Macrophage-Pericyte Axis Directs Tissue Restoration via Amphiregulin-Induced Transforming Growth Factor Beta Activation.

The epidermal growth factor receptor ligand Amphiregulin has a well-documented role in the restoration of tissue homeostasis after injury; however, the mechanism by which Amphiregulin contributes to wound repair remains unknown. Here we show that Amphiregulin functioned by releasing bioactive transforming growth factor beta (TGF-ß) from latent complexes via integrin-αV activation. Using acute injury models in two different tissues, we found that by inducing TGF-ß activation on mesenchymal stromal cells (pericytes), Amphiregulin induced their differentiation into myofibroblasts, thereby selectively contributing to the restoration of vascular barrier function within injured tissue. Furthermore, we identified macrophages as a critical source of Amphiregulin, revealing a direct effector mechanism by which these cells contribute to tissue restoration after acute injury. Combined, these observations expose a so far under-appreciated mechanism of how cells of the immune system selectively control the differentiation of tissue progenitor cells during tissue repair and inflammation.

Myeloid cell recruitment versus local proliferation differentiates susceptibility from resistance to filarial infection.

Both TH2-dependent helminth killing and suppression of the TH2 effector response have been attributed to macrophages (MΦ) activated by IL-4 (M(IL-4)). To investigate how M(IL-4) contribute to diverse infection outcomes, the MΦ compartment of susceptible BALB/c mice and more resistant C57BL/6 mice was profiled during infection of the pleural cavity with the filarial nematode, Litomosoides sigmodontis. C57BL/6 mice exhibited a profoundly expanded resident MΦ (resMΦ) population, which was gradually replenished from the bone marrow in an age-dependent manner. Infection status did not alter the bone-marrow derived contribution to the resMΦ population, confirming local proliferation as the driver of resMΦ expansion. Significantly less resMΦ expansion was observed in the susceptible BALB/c strain, which instead exhibited an influx of monocytes that assumed an immunosuppressive PD-L2+ phenotype. Inhibition of monocyte recruitment enhanced nematode killing. Thus, the balance of monocytic vs. resident M(IL-4) numbers varies between inbred mouse strains and impacts infection outcome.

Epidermal Growth Factor Receptor Expression Licenses Type-2 Helper T Cells to Function in a T Cell Receptor-Independent Fashion.

Gastro-intestinal helminth infections trigger the release of interleukin-33 (IL-33), which induces type-2 helper T cells (Th2 cells) at the site of infection to produce IL-13, thereby contributing to host resistance in a T cell receptor (TCR)-independent manner. Here, we show that, as a prerequisite for IL-33-induced IL-13 secretion, Th2 cells required the expression of the epidermal growth factor receptor (EGFR) and of its ligand, amphiregulin, for the formation of a signaling complex between T1/ST2 (the IL-33R) and EGFR. This shared signaling complex allowed IL-33 to induce the EGFR-mediated activation of the MAP-kinase signaling pathway and consequently the expression of IL-13. Lack of EGFR expression on T cells abrogated IL-13 expression in infected tissues and impaired host resistance. EGFR expression on Th2 cells was TCR-signaling dependent, and therefore, our data reveal a mechanism by which antigen presentation controls the innate effector function of Th2 cells at the site of inflammation.

Tissue-specific contribution of macrophages to wound healing.

Macrophages are present in all tissues, either as resident cells or monocyte-derived cells that infiltrate into tissues. The tissue site largely determines the phenotype of tissue-resident cells, which help to maintain tissue homeostasis and act as sentinels of injury. Both tissue resident and recruited macrophages make a substantial contribution to wound healing following injury. In this review, we evaluate how macrophages in two fundamentally distinct tissues, i.e. the lung and the skin, differentially contribute to the process of wound healing. We highlight the commonalities of macrophage functions during repair and contrast them with distinct, tissue-specific functions that macrophages fulfill during the different stages of wound healing.