Severe or therapy-resistant asthma is increasingly recognised as a major unmet need. A Task Force, supported by the European Respiratory Society and American Thoracic Society, reviewed the definition and provided recommendations and guidelines on the evaluation and treatment of severe asthma in children and adults. A literature review was performed, followed by discussion by an expert committee according to the GRADE (Grading of Recommendations, Assessment, Development and Evaluation) approach for development of specific clinical recommendations. When the diagnosis of asthma is confirmed and comorbidities addressed, severe asthma is defined as asthma that requires treatment with high dose inhaled corticosteroids plus a second controller and/or systemic corticosteroids to prevent it from becoming “uncontrolled” or that remains “uncontrolled” despite this therapy. Severe asthma is a heterogeneous condition consisting of phenotypes such as eosinophilic asthma. Specific recommendations on the use of sputum eosinophil count and exhaled nitric oxide to guide therapy, as well as treatment with anti-IgE antibody, methotrexate, macrolide antibiotics, antifungal agents and bronchial thermoplasty are provided. Coordinated research efforts for improved phenotyping will provide safe and effective biomarker-driven approaches to severe asthma therapy.

/pdf/international-ers-ats-guidelines-on-definition-evaluation-sedelwbk4v.pdf

International ERS/ATS guidelines on definition, evaluation and treatment of severe asthma

Acute inflammation normally resolves by mechanisms that have remained somewhat elusive. Emerging evidence now suggests that an active, coordinated program of resolution initiates in the first few hours after an inflammatory response begins. After entering tissues, granulocytes promote the switch of arachidonic acid–derived prostaglandins and leukotrienes to lipoxins, which initiate the termination sequence. Neutrophil recruitment thus ceases and programmed death by apoptosis is engaged. These events coincide with the biosynthesis, from omega-3 polyunsaturated fatty acids, of resolvins and protectins, which critically shorten the period of neutrophil infiltration by initiating apoptosis. Consequently, apoptotic neutrophils undergo phagocytosis by macrophages, leading to neutrophil clearance and release of anti-inflammatory and reparative cytokines such as transforming growth factor-β1. The anti-inflammatory program ends with the departure of macrophages through the lymphatics. Understanding these and further details of the mechanism required for inflammation resolution may underpin the development of drugs that can resolve inflammatory processes in directed and controlled ways.

Resolution of inflammation: the beginning programs the end.

Transforming growth factor-beta (TGF-beta) is a potent regulatory cytokine with diverse effects on hemopoietic cells. The pivotal function of TGF-beta in the immune system is to maintain tolerance via the regulation of lymphocyte proliferation, differentiation, and survival. In addition, TGF-beta controls the initiation and resolution of inflammatory responses through the regulation of chemotaxis, activation, and survival of lymphocytes, natural killer cells, dendritic cells, macrophages, mast cells, and granulocytes. The regulatory activity of TGF-beta is modulated by the cell differentiation state and by the presence of inflammatory cytokines and costimulatory molecules. Collectively, TGF-beta inhibits the development of immunopathology to self or nonharmful antigens without compromising immune responses to pathogens. This review highlights the findings that have advanced our understanding of TGF-beta in the immune system and in disease.

Transforming growth factor-beta regulation of immune responses.

It used to be easy. In the old days ( 8 years ago), activated macrophages were simply defined as cells that secreted inflammatory mediators and killed intracellular pathogens. Things are becoming progressively more complicated in the world of leukocyte biology. Activated macrophages may be a more heterogenous group of cells than originally appreciated, with different physiologies and performing distinct immunological functions. The first hint of this heterogeneity came with the characterization of the “alternatively activated macrophage” [1]. The exposure of macrophages to interleukin (IL)-4 or glucocorticoids induced a population of cells that up-regulated certain phagocytic receptors but failed to produce nitrogen radicals [2] and as a result, were relatively poor at killing intracellular pathogens. Recent studies have shown that these alternatively activated cells produce several components involved in the synthesis of the extracellular matrix (ECM) [3], suggesting their primary role may be involved in tissue repair rather than microbial killing. It turns out that the name alternatively activated macrophage may be unfortunate for a few reasons. First, although these cells express some markers of activation, they have not been exposed to the classical, activating stimuli, interferon(IFN) and lipopolysaccharide (LPS). Second, and more importantly, the name implies that this is the only other way to activate a macrophage. Recent studies suggest that this may not be the case. Exposure of macrophages to classical activating signals in the presence of immunoglobulin G (IgG) immune complexes induced the production of a cell type that was fundamentally different from the classically activated macrophage. These cells generated large amounts of IL-10 and as a result, were potent inhibitors of acute inflammatory responses to bacterial endotoxin [4]. These activated macrophages have been called type 2-activated macrophages [5] because of their ability to induce T helper cell type 2 (Th2) responses that were predominated by IL-4 [6], leading to IgG class-switching by B cells. Thus, at this time, there appears to be at least three different populations of activated macrophages with three distinct biological functions. The first and most well described is the classically activated macrophage whose role is as an effector cell in Th1 cellular immune responses. The second type of cell, the alternatively activated macrophage, appears to be involved in immunosuppression and tissue repair. The most recent addition to this list is the type 2-activated macrophage, which is anti-inflammatory and preferentially induces Th2-type humoral-immune responses to antigen. Together, these three populations of cells may form their own regulatory network to prevent a well-intentioned immune response from progressing to immunopathology. THE CLASSICALLY ACTIVATED MACROPHAGE

https://jlb.onlinelibrary.wiley.com/doi/epdf/10.1189/jlb.0602325

The many faces of macrophage activation

Macrophages (MPs) are important for skeletal muscle regeneration in vivo and may exert beneficial effects on myogenic cell growth through mitogenic and antiapoptotic activities in vitro. However, MPs are highly versatile and may exert various, and even opposite, functions depending on their activation state. We studied monocyte (MO)/MP phenotypes and functions during skeletal muscle repair. Selective labeling of circulating MOs by latex beads in CX3CR1GFP/+ mice showed that injured muscle recruited only CX3CR1lo/Ly-6C+ MOs from blood that exhibited a nondividing, F4/80lo, proinflammatory profile. Then, within muscle, these cells switched their phenotype to become proliferating antiinflammatory CX3CR1hi/Ly-6C− cells that further differentiated into F4/80hi MPs. In vitro, phagocytosis of muscle cell debris induced a switch of proinflammatory MPs toward an antiinflammatory phenotype releasing transforming growth factor β1. In co-cultures, inflammatory MPs stimulated myogenic cell proliferation, whereas antiinflammatory MPs exhibited differentiating activity, assessed by both myogenin expression and fusion into myotubes. Finally, depletion of circulating MOs in CD11b–diphtheria toxin receptor mice at the time of injury totally prevented muscle regeneration, whereas depletion of intramuscular F4/80hi MPs at later stages reduced the diameter of regenerating fibers. In conclusion, injured skeletal muscle recruits MOs exhibiting inflammatory profiles that operate phagocytosis and rapidly convert to antiinflammatory MPs that stimulate myogenesis and fiber growth.

https://rupress.org/jem/article-pdf/204/5/1057/1161672/jem_20070075.pdf

Inflammatory monocytes recruited after skeletal muscle injury switch into antiinflammatory macrophages to support myogenesis

Ingestion of apoptotic cells in vitro by macrophages induces TGF-beta1 secretion, resulting in an anti-inflammatory effect and suppression of proinflammatory mediators. Here, we show in vivo that direct instillation of apoptotic cells enhanced the resolution of acute inflammation. This enhancement appeared to require phosphatidylserine (PS) on the apoptotic cells and local induction of TGF-beta1. Working with thioglycollate-stimulated peritonea or LPS-stimulated lungs, we examined the effect of apoptotic cell uptake on TGF-beta1 induction. Viable or opsonized apoptotic human Jurkat T cells, or apoptotic PLB-985 cells, human monomyelocytes that do not express PS during apoptosis, failed to induce TGF-beta1. PS liposomes, or PS directly transferred onto the PLB-985 surface membranes, restored the TGF-beta1 induction. Apoptotic cell instillation into LPS-stimulated lungs reduced proinflammatory chemokine levels in the bronchoalveolar lavage fluid (BALF). Additionally, total inflammatory cell counts in the BALF were markedly reduced 1-5 days after apoptotic cell instillation, an effect that could be reversed by opsonization or coinstillation of TGF-beta1 neutralizing antibody. This reduction resulted from early decrease in neutrophils and later decreases in lymphocytes and macrophages. In conclusion, apoptotic cell recognition and clearance, via exposure of PS and ligation of its receptor, induce TGF-beta1 secretion, resulting in accelerated resolution of inflammation.

/pdf/phosphatidylserine-dependent-ingestion-of-apoptotic-cells-71g21zbzhl.pdf

Phosphatidylserine-dependent ingestion of apoptotic cells promotes TGF-β1 secretion and the resolution of inflammation

Rationale: Clearance of apoptotic cells is crucial to the resolution of inflammation and development of fibrosis, but the process is not well understood in normal or diseased human lungs.Objectives: To determine phagocytosis of apoptotic cells by primary human alveolar macrophages and whether defects in uptake of apoptotic cells are associated with decreases in antiinflammatory/antifibrotic mediators.Methods: Human bronchoalveolar lavage macrophages (AMφs) from normal control subjects and subjects with mild-moderate or severe asthma were examined in vitro for phagocytosis of apoptotic human T-cell line Jurkats and secretion of inflammatory mediators.Measurements and Main Results: AMφs from normal subjects and patients with mild-moderate asthma were able to phagocytose apoptotic cells in response to LPS, resulting in an induction of the antifibrotic and/or antiinflammatory eicosanoids, prostaglandin E2 (PGE2) and 15-hydroxyeicosatetraenoic acid (HETE). In contrast, AMφs from patients with severe asthma had...

https://www.atsjournals.org/doi/pdf/10.1164/rccm.200501-035OC

Defective apoptotic cell phagocytosis attenuates prostaglandin E2 and 15-hydroxyeicosatetraenoic acid in severe asthma alveolar macrophages.

Background TGF-β induces expression of tissue inhibitor of metalloproteinase 1 (TIMP-1), a potent inhibitor of matrix metalloproteinases that controls extracellular matrix metabolism and deposition. IL-13 alone does not induce TIMP-1, but in combination with TGF-β it augments TIMP-1 expression. Although these interactions have implications for remodeling in asthma, little is understood regarding the mechanisms controlling TIMP-1 product. Objective To explore the role of Smads and mitogen-activated protein kinase kinase (MEK)–extracellular signal-regulated kinase (ERK) in the TIMP-1 augmentation by IL-13+TGF-β1 in primary human airway fibroblasts. Methods Real-time PCR, Western blot, ELISA, and transient transfection were used to evaluate the mechanisms of TIMP-1 augmentation. Results IL-13 enhanced TGF-β1–induced Smad-2 and Smad-3 phosphorylation, transient transfection with dominant-negative Smad-2 or Smad-3 decreased TIMP-1 mRNA expression in the presence of TGF-β1 and IL-13+TGF-β1 through inhibition of Smad-2 or Smad-3 phosphorylation. ERK phosphorylation was increased by IL-13 and IL-13+TGF-β1. MEK-ERK inhibition decreased TIMP-1 mRNA/protein to a greater degree after IL-13+TGF-β1 stimulation versus TGF-β1 alone. MEK-ERK inhibition also significantly increased Akt phosphorylation under all conditions and decreased Smad-3 phosphorylation in the presence of IL-13+TGF-β1. In contrast, phosphoinositde-3 kinase–Akt inhibition increased phosphorylation of ERK and Smads, leading to increased TIMP-1. Conclusion These results indicate that IL-13 augments TGF-β1–induced TIMP-1 expression through increased Smad phosphorylation. These increases occur as TGF-β1 downregulates IL-13–induced phosphoinositde-3 kinase activation while leaving the positive effect of IL-13–induced ERK on Smad signaling. Clinical implications This augmentation of TGF-β1–induced TIMP-1 by IL-13 could contribute to the fibrosis and airway remodeling seen in the presence of T H 2 inflammation in asthma.

Mai-Lan N. Huynh

Papers

Phosphatidylserine-dependent ingestion of apoptotic cells promotes TGF-β1 secretion and the resolution of inflammation

Defective apoptotic cell phagocytosis attenuates prostaglandin E2 and 15-hydroxyeicosatetraenoic acid in severe asthma alveolar macrophages.

Mechanisms of tissue inhibitor of metalloproteinase 1 augmentation by IL-13 on TGF-β1–stimulated primary human fibroblasts

Transforming Growth Factor-β1 Secretion From Murine Macrophages Is Released by In Vivo Ingestion of Apoptotic Cells