PI3-Kinase-γ Has a Distinct and Essential Role in Lung-Specific Dendritic Cell Development

Immmunometabolism of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a potentially fatal chronic autoimmune disease which is underlain by complex dysfunction of the innate and adaptive immune systems. Although a series of well-defined genetic and environmental factors have been implicated in disease etiology, neither the development nor the persistence of SLE is well understood. Given that several disease susceptibility genes and environmental factors interact and influence inflammatory lineage specification through metabolism, the field of immunometabolism has become a forefront of cutting edge research. Along these lines, metabolic checkpoints of pathogenesis have been identified as targets of effective therapeutic interventions in mouse models and validated in clinical trials. Ongoing studies focus on mitochondrial oxidative stress, activation of the mechanistic target of rapamycin, calcium signaling, glucose utilization, tryptophan degradation, and metabolic cross-talk between gut microbiota and the host immune system.

Identification of Fangji Huangqi Tang as a potential herbal formula for Sjogren syndrome treatment via network pharmacology and experimental validation

Fangji Huangqi Tang (FHT) is a well-known Chinese herbal formula that is prescribed as treatment for rheumatoid diseases. In this study, we aimed to investigate the potential therapeutic targets, efficacy, and safety of FHT in the treatment of Sjogren's syndrome (SS). The Gene Expression Omnibus (GEO) database was used to screen differentially expressed genes (DEGs) in SS. Further, gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to explore the potential biological functions of the DEGs. Subsequently, an FHT-herb-active compound-target network was constructed to identify the relationship between the active compounds in FHT and the related targets. Then, enrichment analysis involving the DEGs and protein-protein interaction (PPI) network analysis were performed to analyze the biological functions of potential targets and screen hub genes. Further, molecular docking was employed to verify the binding affinity between the active compounds and the hub targets, and in vivo experiments involving NOD/LtJ mice were conducted to verify the therapeutic effects of FHT on SS-like symptoms. Finally, inhibition of PIK3CK/Akt pathway by FHT was validated by WB and rt-qPCR. A total of 1836 DEGs were identified in SS based on the GSE159574 dataset, and 114 targets of the active compounds in FHT were screened. Further, via network pharmacology analysis and molecular docking, six active compounds and five hub targets were obtained, and enrichment analysis showed that the anti-SS effect of FHT was predominantly associated with immune cells, such as T cells and neutrophils. In vivo, FHT effectively reduced lymphocyte infiltration foci, increased saliva flow rate, and inhibited increases in the levels of SS-related autoantibodies (anti-SSA and anti-SSB). Furthermore, the biosafety of FHT was verified via the serological examination of liver and kidney function. WB and rt-qPCR analysis confirmed that FHT could inhibit the expression of PIK3CG and the activation of PIK3CG/Akt pathway. Via network pharmacological analysis, molecular docking, and in vivo verification, we demonstrated the multicomponent and multitarget characteristics of FHT in SS treatment, thereby providing novel insights into the pathogenesis of SS and the therapeutic targets of FHT for SS.

The role of PI3Kγ in the immune system: new insights and translational implications

Over the past two decades, new insights have positioned phosphoinositide 3-kinase-γ (PI3Kγ) as a context-dependent modulator of immunity and inflammation. Recent advances in protein structure determination and drug development have allowed for generation of highly specific PI3Kγ inhibitors, with the first now in clinical trials for several oncology indications. Recently, a monogenic immune disorder caused by PI3Kγ deficiency was discovered in humans and modelled in mice. Human inactivated PI3Kγ syndrome confirms the immunomodulatory roles of PI3Kγ and strengthens newly defined roles of this molecule in modulating inflammatory cytokine release in macrophages. Here, we review the functions of PI3Kγ in the immune system and discuss how our understanding of its potential as a therapeutic target has evolved.

Class I PI3K regulatory subunits control differentiation of dendritic cell subsets and regulate Flt3L mediated signal transduction

Dendritic cells (DCs) play pivotal roles in initiating and shaping both innate and adaptive immune responses. The spatiotemporal expression of transcription factor networks and activation of specific signal transduction pathways determine the specification, distribution and differentiation of DC subsets. Even though pioneering studies have established indispensable roles for specific catalytic subunits (p110δ and p110γ) in immune cells, functions of the regulatory subunits, particularly of Class I PI3K, within the hematopoietic system remain incompletely understood. In the study presented here, we deleted the key regulatory subunits—p85α and p85β of the Class I_A PI3K in hematopoietic cells and studied its impact on DC differentiation. Our studies identify that a deficiency of p85 causes increased differentiation of conventional DC (cDC) 2 and plasmacytoid DC (pDC) subsets in the spleen. On the other hand, DC numbers in the bone marrow (BM), thymus and lymph nodes were decreased in p85 mutant mice. Analysis of DC-specific progenitors and precursors indicated increased numbers in the BM and spleen of p85 deficient mice. In-vitro differentiation studies demonstrated augmented DC-differentiation capacities of p85 deficient BM cells in the presence of GM-CSF and Flt3L. BM chimera studies established that p85 deficiency affects DC development through cell intrinsic mechanisms. Molecular studies revealed increased proliferation of DCs and common DC progenitors (CDPs) in the absence of p85 and altered signal transduction pathways in p85 mutant DC subsets in response to Flt3L. In essence, data presented here, for the first time, unequivocally establish that the P85α subunit of class I_A PI3Ks has an indispensable role in the development and maintenance of DCs.

Dendritic Cells and Their Immunotherapeutic Potential for Treating Type 1 Diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells through a process that is primarily mediated by T cells. Emerging evidence suggests that dendritic cells (DCs) play a crucial role in initiating and developing this debilitating disease. DCs are professional antigen-presenting cells with the ability to integrate signals arising from tissue infection or injury that present processed antigens from these sites to naïve T cells in secondary lymphoid organs, thereby triggering naïve T cells to differentiate and modulate adaptive immune responses. Recent advancements in our knowledge of the various subsets of DCs and their cellular structures and methods of orchestration over time have resulted in a better understanding of how the T cell response is shaped. DCs employ various arsenal to maintain their tolerance, including the induction of effector T cell deletion or unresponsiveness and the generation and expansion of regulatory T cell populations. Therapies that suppress the immunogenic effects of dendritic cells by blocking T cell costimulatory pathways and proinflammatory cytokine production are currently being sought. Moreover, new strategies are being developed that can regulate DC differentiation and development and harness the tolerogenic capacity of these cells. Here, in this report, we focus on recent advances in the field of DC immunology and evaluate the prospects of DC-based therapeutic strategies to treat T1D.

A dominant function of LynB kinase in preventing autoimmunity

Here, we report that the LynB splice variant of the Src-family kinase Lyn exerts a dominant immunosuppressive function in vivo, whereas the LynA isoform is uniquely required to restrain autoimmunity in female mice. We used CRISPR-Cas9 gene editing to constrain lyn splicing and expression, generating single-isoform LynA knockout (LynAKO) or LynBKO mice. Autoimmune disease in total LynKO mice is characterized by production of antinuclear antibodies, glomerulonephritis, impaired B cell development, and overabundance of activated B cells and proinflammatory myeloid cells. Expression of LynA or LynB alone uncoupled the developmental phenotype from the autoimmune disease: B cell transitional populations were restored, but myeloid cells and differentiated B cells were dysregulated. These changes were isoform-specific, sexually dimorphic, and distinct from the complete LynKO. Despite the apparent differences in disease etiology and penetrance, loss of either LynA or LynB had the potential to induce severe autoimmune disease with parallels to human systemic lupus erythematosus (SLE).

Chemo- and mechanosensing by dendritic cells facilitate antigen surveillance in the spleen

Spleen dendritic cells (DC) are critical for initiation of adaptive immune responses against blood-borne invaders. Key to DC function is their positioning at sites of pathogen entry, and their abilities to selectively capture foreign antigens and promptly engage T cells. Focusing on conventional DC2 (cDC2), we discuss the contribution of chemoattractant receptors (EBI2 or GPR183, S1PR1, and CCR7) and integrins to cDC2 positioning and function. We give particular attention to a newly identified role in cDC2 for adhesion G-protein coupled receptor E5 (Adgre5 or CD97) and its ligand CD55, detailing how this mechanosensing system contributes to splenic cDC2 positioning and homeostasis. Additional roles of CD97 in the immune system are reviewed. The ability of cDC2 to be activated by circulating missing self-CD47 cells and to integrate multiple red blood cell (RBC)-derived inputs is discussed. Finally, we describe the process of activated cDC2 migration to engage and prime helper T cells. Throughout the review, we consider the insights into cDC function in the spleen that have emerged from imaging studies.

Tissue-resident macrophages: guardians of organ homeostasis

Tissue-resident macrophages (M_TR) have recently emerged as a key rheostat capable of regulating the balance between organ health and disease. In most organs, ontogenetically and functionally distinct macrophage subsets fulfill a plethora of functions specific to their tissue environment. In this review, we summarize recent findings regarding the ontogeny and functions of macrophage populations in different mammalian tissues, describing how these cells regulate tissue homeostasis and how they can contribute to inflammation. Furthermore, we highlight new developments concerning certain general principles of tissue macrophage biology, including the importance of metabolism for understanding macrophage activation states and the influence of intrinsic and extrinsic factors on macrophage metabolic control. We also shed light on certain open questions in the field and how answering these might pave the way for tissue-specific therapeutic approaches.

Stromal Cell-Contact Dependent PI3K and APRIL Induced NF-κB Signaling Prevent Mitochondrial- and ER Stress Induced Death of Memory Plasma Cells

The persistence of long-lived memory plasma cells in the bone marrow depends on survival factors available in the bone marrow, which are provided in niches organized by stromal cells. Using an ex vivo system in which we supply the known survival signals, direct cell contact to stromal cells, and the soluble cytokine a proliferation-inducing ligand (APRIL), we have elucidated the critical signaling pathways required for the survival of long-lived plasma cells. Integrin-mediated contact of bone marrow plasma cells with stromal cells activates the phosphatidylinositol 3-kinase (PI3K) signaling pathway, leading to critical inactivation of Forkhead-Box-Protein O1/3 (FoxO1/3) and preventing the activation of mitochondrial stress-associated effector caspases 3 and 7. Accordingly, inhibition of PI3K signaling in vivo ablates bone marrow plasma cells. APRIL signaling, by the nuclear factor κB (NF-κB) pathway, blocks activation of the endoplasmic-reticulum-stress-associated initiator caspase 12. Thus, stromal-cell-contact-induced PI3K and APRIL-induced NF-κB signaling provide the necessary and complementary signals to maintain bone marrow memory plasma cells.

GM-CSF instigates a dendritic cell-T-cell inflammatory circuit that drives chronic asthma development

BACKGROUND

Steroid-resistant asthma is often characterized by high levels of neutrophils and mixed T_H2/T_H17 immune profiles. Indeed, neutrophils are key drivers of chronic lung inflammation in multiple respiratory diseases. Their numbers correlate strongly with disease severity, and their presence is often associated with exacerbation of chronic lung inflammation.

OBJECTIVE

What factors drive development of neutrophil-mediated chronic lung disease remains largely unknown, and we sought to study the role of GM-CSF as a potential regulator in chronic asthma.

METHODS

Different experimental animal models of chronic asthma were used in combination with alveolar macrophage-reconstitution of global GM-CSF receptor knockout mice as well as cell-type-specific knockout animals to elucidate the role of GM-CSF signaling in chronic airway inflammation.

RESULTS

We identify GM-CSF signaling as a critical factor regulating pulmonary accumulation of neutrophils. We show that although being not required for intrinsically regulating neutrophil migration, GM-CSF controls lung dendritic cell function, which in turn promotes T-cell-dependent recruitment of neutrophils to the airways. We demonstrate that GM-CSF regulates lung dendritic cell antigen uptake, transport, and T_H2/T_H17 cell priming in an intrinsic fashion, which in turn drives pulmonary granulocyte recruitment and contributes to development of airway hyperresponsiveness in chronic disease.

CONCLUSIONS

We identify GM-CSF as a potentially novel therapeutic target in chronic lung inflammation, describing a GM-CSF-dependent lung conventional dendritic cell-T-cell-neutrophil axis that drives chronic lung disease.

What Makes the Lung Unique – Tissue-Specific Immunity in the Respiratory Tract

The immune system constitutes a critical mechanism of the human body to preserve health and mitigate disease. In the lung, immunity is seen as a critical driver in many respiratory diseases, in particular in those characterised by aberrant inflammation, such as chronic obstructive pulmonary disease, fibrosis, and asthma. In this review, the specialised set of immune cells and lung tissue-specific regulators, including key cytokines such as granulocyte-macrophage colony-stimulating factor and transforming growth factor β, that control immune responses in the respiratory tract will be discussed. Furthermore, the current understanding of the impact of key environmental components such as the role of oxygen and lung microbiota on lung immunity will be highlighted. The goal is to identify the unique aspects of lung immune biology to facilitate insights into the aetiology of common lung inflammatory diseases and to provide the basis for a deeper mechanistic understanding of the underlying immune processes. Finally, key future avenues of research such as using more comprehensive quantitative approaches for elucidating molecular disease mechanisms as well as the potential to exploit tissue-specific regulators of immunity for therapy of lung inflammatory disorders will be discussed.

Function, Regulation and Biological Roles of PI3Kγ Variants

Phosphatidylinositide 3-kinase (PI3K) γ is the only class IB PI3K member playing significant roles in the G-protein-dependent regulation of cell signaling in health and disease. Originally found in the immune system, increasing evidence suggest a wide array of functions in the whole organism. PI3Kγ occur as two different heterodimeric variants: PI3Kγ (p87) and PI3Kγ (p101), which share the same p110γ catalytic subunit but differ in their associated non-catalytic subunit. Here we concentrate on specific PI3Kγ features including its regulation and biological functions. In particular, the roles of its non-catalytic subunits serving as the main regulators determining specificity of class IB PI3Kγ enzymes are highlighted.

TSC1/mTOR-controlled metabolic-epigenetic cross talk underpins DC control of CD8+ T-cell homeostasis

Dendritic cells (DCs) play pivotal roles in T-cell homeostasis and activation, and metabolic programing has been recently linked to DC development and function. However, the metabolic underpinnings corresponding to distinct DC functions remain largely unresolved. Here, we demonstrate a special metabolic–epigenetic coupling mechanism orchestrated by tuberous sclerosis complex subunit 1 (TSC1)-mechanistic target of rapamycin (mTOR) for homeostatic DC function. Specific ablation of Tsc1 in the DC compartment (Tsc1^DC-KO) largely preserved DC development but led to pronounced reduction in naïve and memory–phenotype cluster of differentiation (CD)8⁺ T cells, a defect fully rescued by concomitant ablation of mTor or regulatory associated protein of MTOR, complex 1 (Rptor) in DCs. Moreover, Tsc1^DC-KO mice were unable to launch efficient antigen-specific CD8⁺ T effector responses required for containing Listeria monocytogenes and B16 melanomas. Mechanistically, our data suggest that the steady-state DCs tend to tune down de novo fatty acid synthesis and divert acetyl-coenzyme A (acetyl-CoA) for histone acetylation, a process critically controlled by TSC1-mTOR. Correspondingly, TSC1 deficiency elevated acetyl-CoA carboxylase 1 (ACC1) expression and fatty acid synthesis, leading to impaired epigenetic imprinting on selective genes such as major histocompatibility complex (MHC)-I and interleukin (IL)-7. Remarkably, tempering ACC1 activity was able to divert cytosolic acetyl-CoA for histone acetylation and restore the gene expression program compromised by TSC1 deficiency. Taken together, our results uncover a crucial role for TSC1-mTOR in metabolic programing of the homeostatic DCs for T-cell homeostasis and implicate metabolic-coupled epigenetic imprinting as a paradigm for DC specification.

Dendritic cells (DCs) play pivotal roles in T cell homeostasis and activation, but the basis of the metabolic programming of distinct DC functions remains unclear. This study identifies a novel metabolic-epigenetic node enabling DC control of CD8 T cell homeostasis, involving mTOR-ACC1 as a rheostat that balances fatty-acid synthesis and histone acetylation.

Metabolic Control of Dendritic Cell Functions: Digesting Information

Dendritic cells (DCs) control innate and adaptive immunity by patrolling tissues to gather antigens and danger signals derived from microbes and tissue. Subsequently, DCs integrate those environmental cues, orchestrate immunity or tolerance, and regulate tissue homeostasis. Recent advances in the field of immunometabolism highlight the notion that immune cells markedly alter cellular metabolic pathways during differentiation or upon activation, which has important implications on their functionality. Previous studies showed that active oxidative phosphorylation in mitochondria is associated with immature or tolerogenic DCs, while increased glycolysis upon pathogen sensing can promote immunogenic DC functions. However, new results in the last years suggest that regulation of DC metabolism in steady state, after immunogenic activation and during tolerance in different pathophysiological settings, may be more complex. Moreover, ontogenically distinct DC subsets show different functional specializations to control T cell responses. It is, thus, relevant how metabolism influences DC differentiation and plasticity, and what potential metabolic differences exist among DC subsets. Better understanding of the emerging connection between metabolic adaptions and functional DC specification will likely allow the development of therapeutic strategies to manipulate immune responses.

The Isoform Selective Roles of PI3Ks in Dendritic Cell Biology and Function

Phosphoinositide-3 kinases (PI3Ks) generate 3-phosphorylated phosphoinositide lipids that are implicated in many biological processes in homeostatic states and pathologies such as cancer, inflammation and autoimmunity. Eight isoforms of PI3K exist in mammals and among them the class I PI3K, p110γ, and PI3Kδ, and class III Vps34 being the most expressed and well characterized in immune cells. Following engagement of pathogen recognition receptors (PRRs), PI3Ks coordinate vital cellular processes of signaling and vesicular trafficking in innate phagocytes such as macrophages and professional antigen presenting dendritic cells (DCs). Although previous studies demonstrated the involvement of PI3K isoforms in innate and adaptive immune cell types, the role of PI3Ks with respect to DC biology has been enigmatic. Thus, this review, based on studies involving PI3K isoforms, highlight how the different PI3Ks isoforms could regulate DC functions such as antigen processing and presentation including PRR responses.

The impact of metabolic reprogramming on dendritic cell function

Dendritic cells (DCs) are antigen-presenting cells with the ability to activate naïve T cells and direct the adaptive cellular immune response toward a specific profile. This is important, as different pathogens demand specific "profiles" of immune responses for their elimination. Such a goal is achieved depending on the maturation/activation status of DCs by the time of antigen presentation to T cells. Notwithstanding this, recent studies have shown that DCs alter their metabolic program to accommodate the functional changes in gene expression and protein synthesis that follow antigen recognition. In this review, we aim to summarize the data in the literature regarding the metabolic pathways involved with DC phenotypes and their functions.

PPAR-γ in innate and adaptive lung immunity

The transcription factor PPAR-γ (peroxisome proliferator-activated receptor-γ) is a key regulator of lung immunity exhibiting multiple cell type specific roles in controlling development and function of the lung immune system. It is strictly required for the generation of alveolar macrophages by controlling differentiation of fetal lung monocyte precursors. Furthermore, it plays an important role in lung allergic inflammation by licensing lung dendritic cell t helper 2 (Th2) priming capacity as well as acting as a master transcription factor for pathogenic Th2 cells. Due to this plethora of functions and its involvement in multiple pulmonary diseases including asthma and pulmonary alveolar proteinosis, understanding the role of PPAR-γ in lung immunity is an important subject of ongoing research.

Metabolic control of cell fate bifurcations in a hematopoietic progenitor population

Growth signals drive hematopoietic progenitor cells to proliferate and branch into divergent cell fates, but how unequal outcomes arise from a common progenitor is not fully understood. We used steady-state analysis of in vivo hematopoiesis and Fms-related tyrosine kinase 3 ligand (Flt3L)-induced in vitro differentiation of dendritic cells (DCs) to determine how growth signals regulate lineage bias. We found that Flt3L signaling induced anabolic activation and proliferation of DC progenitors, which was associated with DC differentiation. Perturbation of processes associated with quiescence and catabolism, including AMP-activated protein kinase signaling, fatty acid oxidation, or mitochondrial clearance increased development of cDC2 cells at the expense of cDC1 cells. Conversely, scavenging anabolism-associated reactive oxygen species skewed differentiation toward cDC1 cells. Sibling daughter cells of dividing DC progenitors exhibited unequal expression of the transcription factor interferon regulatory factor 8, which correlated with clonal divergence in FoxO3a signaling and population-level bifurcation of cell fate. We propose that unequal transmission of growth signals during cell division might support fate branches during proliferative expansion of progenitors.

MiR221 promotes precursor B-cell retention in the bone marrow by amplifying the PI3K-signaling pathway in mice

Hematopoietic stem cells and lineage-uncommitted progenitors are able to home to the bone marrow upon transplantation and reconstitute the host with hematopoietic progeny. Expression of miR221 in B-lineage committed preBI-cells induces their capacity to home to the bone marrow. However, the molecular mechanisms underlying miR221-controlled bone marrow homing and retention remain poorly understood. Here, we demonstrate, that miR221 regulates bone marrow retention of such B-cell precursors by targeting PTEN, thus enhancing PI3K signaling in response to the chemokine CXCL12. MiR221-enhanced PI3K signaling leads to increased expression of the anti-apoptotic protein Bcl2 and VLA4 integrin-mediated adhesion to VCAM1 in response to CXCL12 in vitro. Ablation of elevated PI3K activity abolishes the retention of miR221 expressing preBI-cells in the bone marrow. These results suggest that amplification of PI3K signaling by miR221 could be a general mechanism for bone marrow residence, shared by miR221-expressing hematopoietic cells.

Metabolic Plasticity in Dendritic Cell Responses: Implications in Allergic Asthma

Dendritic cells (DCs) are highly specialized in antigen presentation and play a pivotal role in the initiation, progression, and perpetuation of adaptive immune responses. Emerging immune pathways are being recognized increasingly for DCs and their subsets that differentially regulate T lymphocyte function based on the type and interactions with the antigen. However, these interactions not only alter the signaling process and DC function but also render metabolic plasticity. The current review focuses on the metabolic cues of DCs that coordinate DC activation and differentiation and discuss whether targeting these fundamental cellular processes have implications to control airway inflammation and adaptive immunity. Therefore, strategies using metabolism-based therapeutic manipulation of DC functions could be developed into novel treatments for airway inflammation and asthma.

PPARγ in dendritic cells and T cells drives pathogenic type-2 effector responses in lung inflammation

Type-2 immune responses are well-established drivers of chronic inflammatory diseases, such as asthma, and represent a large burden on public health systems. The transcription factor PPARγ is known to promote M2-macrophage and alveolar macrophage development. Here, we report that PPARγ plays a key role in both T cells and dendritic cells (DCs) for development of type-2 immune responses. It is predominantly expressed in mouse Th2 cells in vitro and in vivo as well as human Th2 cells from allergic patients. Using conditional knockouts, we show that PPARγ signaling in T cells, although largely dispensable for IL-4 induction, is critical for IL-33-driven Th2 effector function in type-2 allergic airway responses. Furthermore, we demonstrate that IL-4 and IL-33 promote up-regulation of PPARγ in lung-resident CD11b+ DCs, which enhances migration to draining lymph nodes and Th2 priming capacity. Thus, we uncover a surprising proinflammatory role for PPARγ and establish it as a novel, important mediator of DC-T cell interactions in type-2 immunity.

MenTORing Immunity: mTOR Signaling in the Development and Function of Tissue-Resident Immune Cells

Tissue-resident immune cells must balance survival in peripheral tissues with the capacity to respond rapidly upon infection or tissue damage, and in turn couple these responses with intrinsic metabolic control and conditions in the tissue microenvironment. The serine/threonine kinase mammalian/mechanistic target of rapamycin (mTOR) is a central integrator of extracellular and intracellular growth signals and cellular metabolism and plays important roles in both innate and adaptive immune responses. This review discusses the function of mTOR signaling in the differentiation and function of tissue-resident immune cells, with focus on the role of mTOR as a metabolic sensor and its impact on metabolic regulation in innate and adaptive immune cells. We also discuss the impact of metabolic constraints in tissues on immune homeostasis and disease, and how manipulating mTOR activity with drugs such as rapamycin can modulate immunity in these contexts.

mTOR regulates metabolic adaptation of APCs in the lung and controls the outcome of allergic inflammation

Antigen-presenting cells (APCs) occupy diverse anatomical tissues, but their tissue-restricted homeostasis remains poorly understood. Here, working with mouse models of inflammation, we found that mechanistic target of rapamycin (mTOR)-dependent metabolic adaptation was required at discrete locations. mTOR was dispensable for dendritic cell (DC) homeostasis in secondary lymphoid tissues but necessary to regulate cellular metabolism and accumulation of CD103⁺ DCs and alveolar macrophages in lung. Moreover, while numbers of mTOR-deficient lung CD11b⁺ DCs were not changed, they were metabolically reprogrammed to skew allergic inflammation from eosinophilic T helper cell 2 (T_H2) to neutrophilic T_H17 polarity. The mechanism for this change was independent of translational control but dependent on inflammatory DCs, which produced interleukin-23 and increased fatty acid oxidation. mTOR therefore mediates metabolic adaptation of APCs in distinct tissues, influencing the immunological character of allergic inflammation.

Regulated IRE1-dependent mRNA decay sets the threshold for dendritic cell survival

The IRE1-XBP1 signalling pathway is part of a cellular programme that protects against endoplasmic reticulum (ER) stress, but also controls development and survival of immune cells. Loss of XBP1 in splenic type 1 conventional dendritic cells (cDC1s) results in functional alterations without affecting cell survival. However, in mucosal cDC1s, loss of XBP1 impaired survival in a tissue-specific manner-while lung cDC1s die, intestinal cDC1s survive. This was not caused by differential activation of ER stress cell-death regulators CHOP or JNK. Rather, survival of intestinal cDC1s was associated with their ability to shut down protein synthesis through a protective integrated stress response and their marked increase in regulated IRE1-dependent messenger RNA decay. Furthermore, loss of IRE1 endonuclease on top of XBP1 led to cDC1 loss in the intestine. Thus, mucosal DCs differentially mount ATF4- and IRE1-dependent adaptive mechanisms to survive in the face of ER stress.

The Multifaceted Roles of PI3Kγ in Hypertension, Vascular Biology, and Inflammation

PI3Kγ is a multifaceted protein, crucially involved in cardiovascular and immune systems. Several studies described the biological and physiological functions of this enzyme in the regulation of cardiovascular system, while others stressed its role in the modulation of immunity. Although PI3Kγ has been historically investigated for its role in leukocytes, the last decade of research also dedicated efforts to explore its functions in the cardiovascular system. In this review, we report an overview recapitulating how PI3Kγ signaling participates in the regulation of vascular functions involved in blood pressure regulation. Moreover, we also summarize the main functions of PI3Kγ in immune responses that could be potentially important in the interaction with the cardiovascular system. Considering that vascular and immune mechanisms are increasingly emerging as intertwining players in hypertension, PI3Kγ could be an intriguing pathway acting on both sides. The availability of specific inhibitors introduces a perspective of further translational research and clinical approaches that could be exploited in hypertension.

PI3Kγ Is Critical for Dendritic Cell-Mediated CD8+ T Cell Priming and Viral Clearance during Influenza Virus Infection

Phosphoinositide-3-kinases have been shown to be involved in influenza virus pathogenesis. They are targeted directly by virus proteins and are essential for efficient viral replication in infected lung epithelial cells. However, to date the role of PI3K signaling in influenza infection in vivo has not been thoroughly addressed. Here we show that one of the PI3K subunits, p110γ, is in fact critically required for mediating the host’s antiviral response. PI3Kγ deficient animals exhibit a delayed viral clearance and increased morbidity during respiratory infection with influenza virus. We demonstrate that p110γ is required for the generation and maintenance of potent antiviral CD8+ T cell responses through the developmental regulation of pulmonary cross-presenting CD103+ dendritic cells under homeostatic and inflammatory conditions. The defect in lung dendritic cells leads to deficient CD8+ T cell priming, which is associated with higher viral titers and more severe disease course during the infection. We thus identify PI3Kγ as a novel key host protective factor in influenza virus infection and shed light on an unappreciated layer of complexity concerning the role of PI3K signaling in this context.

Acute respiratory viral infections like influenza virus can cause life-threatening disease in infected individuals. Phosphoinositide-3-kinases have been suggested to be important factors used by the virus to infect and replicate in host cells, and thereby cause viral pneumonia. However, to date the role of these signaling molecules has not been thoroughly addressed in the context of an infection in whole animals, rather than just cell culture systems. Here we show that one of the PI3K subunits, PI3Kγ, is in fact critically required for the clearance of the infection. This is because PI3Kγ regulates the immune response against the virus through the generation and maintenance of antiviral CD8+ T cell responses. We show that in the absence of PI3Kγ a specialized dendritic cell subset in the lung is deficient and this leads to a strongly impaired immune response against influenza virus. We thus identify PI3Kγ as a novel host molecule that is important for the immune defense against influenza virus infection

Origin, Localization, and Immunoregulatory Properties of Pulmonary Phagocytes in Allergic Asthma

Allergic asthma is a chronic inflammatory disease of the airways that is driven by maladaptive T helper 2 (Th2) and Th17 immune responses against harmless, airborne substances. Pulmonary phagocytes represent the first line of defense in the lung where they constantly sense the local environment for potential threats. They comprise two distinct cell types, i.e., macrophages and dendritic cells (DC) that differ in their origins and functions. Alveolar macrophages quickly take up most of the inhaled allergens, yet do not deliver their cargo to naive T cells sampling in draining lymph nodes. In contrast, pulmonary DCs instruct CD4(+) T cells develop into Th2 and Th17 effectors, initiating the maladaptive immune responses toward harmless environmental substances observed in allergic individuals. Unraveling the mechanisms underlying this mistaken identity of harmless, airborne substances by innate immune cells is one of the great challenges in asthma research. The identification of different pulmonary DC subsets, their role in antigen uptake, migration to the draining lymph nodes, and their potential to instruct distinct T cell responses has set the stage to unravel this mystery. However, at this point, a detailed understanding of the spatiotemporal resolution of DC subset localization, allergen uptake, processing, autocrine and paracrine cellular crosstalk, and the humoral factors that define the activation status of DCs is still lacking. In addition to DCs, at least two distinct macrophage populations have been identified in the lung that are either located in the airway/alveolar lumen or in the interstitium. Recent data suggest that such populations can exert either pro- or anti-inflammatory functions. Similar to the DC subsets, detailed insights into the individual roles of alveolar and interstitial macrophages during the different phases of asthma development are still missing. Here, we will provide an update on the current understanding of the origin, localization, and function of the diverse pulmonary antigen-presenting cell subsets, in particular with regard to the development and regulation of allergic asthma. While most data are from mouse models of experimental asthma, we have also included available human data to judge the translational value of the findings obtained in experimental asthma models.