Li Zhen Song

Antielastin autoimmunity in tobacco smoking–induced emphysema

Chronic obstructive pulmonary disease and emphysema are common destructive inflammatory diseases that are leading causes of death worldwide. Here we show that emphysema is an autoimmune disease characterized by the presence of antielastin antibody and T-helper type 1 (TH1) responses, which correlate with emphysema severity. These findings link emphysema to adaptive immunity against a specific lung antigen and suggest the potential for autoimmune pathology of other elastin-rich tissues such as the arteries and skin of smokers.

An Immune Basis for Lung Parenchymal Destruction in Chronic Obstructive Pulmonary Disease and Emphysema

ABSTRACT Background Chronic obstructive pulmonary disease and emphysema are a frequent result of long-term smoking, but the exact mechanisms, specifically which types of cells are associated with the lung destruction, are unclear. Methods and Findings We studied different subsets of lymphocytes taken from portions of human lungs removed surgically to find out which lymphocytes were the most frequent, which cell-surface markers these lymphocytes expressed, and whether the lymphocytes secreted any specific factors that could be associated with disease. We found that loss of lung function in patients with chronic obstructive pulmonary disease and emphysema was associated with a high percentage of CD4+ and CD8+ T lymphocytes that expressed chemokine receptors CCR5 and CXCR3 (both markers of T helper 1 cells), but not CCR3 or CCR4 (markers of T helper 2 cells). Lung lymphocytes in patients with chronic obstructive pulmonary disease and emphysema secrete more interferon gamma—often associated with T helper 1 cells—and interferon-inducible protein 10 and monokine induced by interferon, both of which bind to CXCR3 and are involved in attracting T helper 1 cells. In response to interferon-inducible protein 10 and monokine induced by interferon, but not interferon gamma, lung macrophages secreted macrophage metalloelastase (matrix metalloproteinase-12), a potent elastin-degrading enzyme that causes tissue destruction and which has been linked to emphysema. Conclusions These data suggest that Th1 lymphoctytes in the lungs of people with smoking-related damage drive progression of emphysema through CXCR3 ligands, interferon-inducible protein 10, and monokine induced by interferon.

Decreased allergic lung inflammatory cell egression and increased susceptibility to asphyxiation in MMP2-deficiency

Clearance of recruited immune cells is necessary to resolve inflammatory reactions. We show here that matrix metalloproteinase 2 (MMP2), as part of an interleukin 13 (IL-13)–dependent regulatory loop, dampens inflammation by promoting the egress of inflammatory cells into the airway lumen. MMP2−/− mice showed a robust asthma phenotype and increased susceptibility to asphyxiation induced by allergens. However, whereas the lack of MMP2 reduced the influx of cells into bronchoalveolar lavage (BAL), numerous inflammatory cells accumulated in the lung parenchyma. BAL of MMP2−/− mice lacked normal chemotactic activity, whereas lung inflammatory cells from the same mice showed appropriate chemotactic responses. Thus, MMP2 establishes the chemotactic gradient required for egression of lung inflammatory cells and prevention of lethal asphyxiation.

Overlapping and independent contributions of MMP2 and MMP9 to lung allergic inflammatory cell egression through decreased CC chemokines

The mechanisms that initiate allergic lung inflammation are relevant to expression of diseases such as asthma, but the factors underlying resolution of inflammation are equally important. Previously, we demonstrated the importance of matrix metalloproteinase 2 (MMP2) for airway egression of lung eosinophils, a critical anti‐inflammatory mechanism without which mice are rendered highly susceptible to lethal asphyxiation. Here we show that leukocyte MMP9 is the dominant airway MMP controlling inflammatory cell egression. The allergic lung phenotype of MMP9−/− mice was similar to WT and was not altered by concomitant deletion of the MMP2 gene (double knockout; dko). However, inflammatory cells accumulated aberrantly in the lungs of allergen‐challenged MMP9−/− and dko mice and fewer eosinophils and neutrophils were present in bronchoalveolar lavage. These aberrant cellular trafficking patterns were explained by disruption of transepithelial chemokine gradients, in MMP2−/− mice affecting only eotaxin (CCL11), but in MMP9−/− and dko mice involving eotaxin, MARC (CCL7), and TARC (CCL17). Thus, by establishing multiple transepithelial chemokine gradients, MMP9 is broadly implicated in the resolution of allergic inflammation, an essential protective mechanism that overlaps with a more limited role played by MMP2.

Cleavage of Fibrinogen by Proteinases Elicits Allergic Responses Through Toll-Like Receptor 4

Allergy Induction Proteinases found in fungi and other allergens elicit allergic inflammation, but how they do so is far from clear. It is also unclear how pattern recognition receptors, which detect invading microbes, drive allergic inflammation. Millien et al. (p. 792) shed light on this puzzle by showing that, in mice, induction of allergic inflammation requires proteinase-dependent cleavage of the clotting factor fibrinogen, leading to generation of a ligand that activates the pattern-recognition receptor, Toll-like receptor 4 (TLR4). Cleaved fibrinogen signals through TLR4 to activate the innate immune system and recruit cells to the airway, which drives both allergic responses and antifungal immunity. Allergic inflammation requires proteinase-dependent cleavage of fibrinogen that activates innate immunity through Toll-like receptor 4. Proteinases and the innate immune receptor Toll-like receptor 4 (TLR4) are essential for expression of allergic inflammation and diseases such as asthma. A mechanism that links these inflammatory mediators is essential for explaining the fundamental basis of allergic disease but has been elusive. Here, we demonstrate that TLR4 is activated by airway proteinase activity to initiate both allergic airway disease and antifungal immunity. These outcomes were induced by proteinase cleavage of the clotting protein fibrinogen, yielding fibrinogen cleavage products that acted as TLR4 ligands on airway epithelial cells and macrophages. Thus, allergic airway inflammation represents an antifungal defensive strategy that is driven by fibrinogen cleavage and TLR4 activation. These findings clarify the molecular basis of allergic disease and suggest new therapeutic strategies.

Lung Myeloid Dendritic Cells Coordinately Induce T H 1 and T H 17 Responses in Human Emphysema

Specialized immune cells in the lungs of patients with emphysema create an inflammatory environment that drives lung destruction in a characteristic autoimmune reaction. Dendritic Cells of Destruction Underlie Emphysema Tobacco smoke is never good for your lungs, and in some people it sets up a destructive process called emphysema. In this disease, air sacs that normally exchange carbon dioxide for oxygen become enlarged, ultimately losing their elastic recoil and physiological function. Breathing becomes labored. Even uninfected lungs with emphysema show signs of a complex immune response, with an accumulation of immune cells. To attack the difficult chicken-or-the-egg problem presented by this disease, Shan et al. sorted out which of these cells serve as the ringleaders in orchestrating this immune reaction and, in the process, found the telltale presence of T helper 17 (TH17) cells—a recently identified hallmark of autoimmune inflammation. Cigarette smoke causes irritation in the lung and activates a general defensive reaction via the innate immune system. When this system cannot restore tissue health, the more precise adaptive immune system comes into play. The authors of Shan et al. now show that specialized professional antigen-presenting cells—called dendritic cells—are recruited by a chemoattractant into the lung, where they induce naïve CD4 T cells to develop into TH1 cells. These immune agents then help cytotoxic T cells to target damaged host lung tissue for destruction. Also induced by the dendritic cells are TH17 cells. These specialized T lymphocytes normally protect the barriers between the body and the environment (the skin and the gut lining, for example), but they also congregate at sites in which the body is erroneously attacking itself, as in autoimmune diseases such as rheumatoid arthritis and colitis. The cytokine interleukin-17A secreted by the TH17 cells coordinates their contribution to destruction of the lung in emphysema by causing lung macrophages to secrete two critical molecules: CCL20, a chemoattractant for the dendritic cells, which then set up an inflammatory positive feedback loop, and matrix metalloproteinase 12 (MMP12), a potent enzyme that destroys a lung endogenous protective proteinase called α1-antitrypsin. In the industrialized world, the ultimate cause of emphysema is usually smoking, but in developing countries, smoke from cooking fires and pollution are important factors in the development of this disease, which is a leading cause of death worldwide. Even after removal of the respiratory irritant, the disease progression is only slowed and existing lung damage is irreversible. Medications can ease the shortness of breath but are not a cure. A lung transplant or partial lung removal is a last resort available only to a few fortunate individuals (see Cypel et al. in this issue). Identification of the cellular players—like the dendritic and TH17 cells described by Shan et al.—through which smoke causes lung destruction is a key to discovering drugs that effect damage control. Moreover, the injurious cellular cycles established in the emphysematous lung are likely not unique, and their elucidation will undoubtedly uncover clues to other immune-related diseases that are associated with smoking. Exposure to tobacco smoke activates innate and adaptive immune responses that in long-term smokers have been linked to diseases of the lungs, cardiovascular system, joints, and other organs. The destruction of lung tissue that underlies smoking-induced emphysema has been associated with T helper 1 cells that recognize the matrix protein elastin. Factors that result in the development of such autoreactive T cells in smokers remain unknown but are crucial for further understanding the pathogenesis of systemic inflammatory diseases in smokers. Here, we show that lung myeloid dendritic cells were sufficient to induce T helper 1 and T helper 17 responses in CD4 T cells. T helper 1 and 17 cells are invariably present in lungs from patients with emphysema but not in lungs from normal individuals. Interleukin-17A, a canonical T helper 17 cytokine, enhanced secretion of CCL20, a chemoattractant for dendritic cells, and matrix metalloproteinase 12, a potent elastolytic proteinase, from lung macrophages. Thus, although diverse lung factors potentially contribute to T helper effector differentiation in vivo, lung myeloid dendritic cells direct the generation of pathogenic T cells and support a feedback mechanism that sustains both inflammatory cell recruitment and lung destruction. This mechanism may underlie disease in other elastin-rich organs and tissues.

Cigarette Smoke Induction of Osteopontin (SPP1) Mediates T H 17 Inflammation in Human and Experimental Emphysema

The destruction of lung tissue in emphysema is orchestrated by antigen-presenting cells that have been activated by smoke. When Smoke Gets in Your Lungs Even without the warning label on the cigarette box, everyone knows that tobacco smoke is bad for you. But what really happens inside the lung to cause disease? Shan et al. have married studies in patients with emphysema and in mice exposed to tobacco smoke for several months to identify some of the crucial events that cause one serious lung disease—emphysema. They find that the antigen-presenting cells of the immune system are culpable; indeed, transfer of these cells from a mouse with emphysema into a healthy mouse induces disease. Further, they identify the signaling molecules in these cells that are activated by smoke (osteopontin and the transcription factor Irf7), which may prove to be useful targets for therapies. First, the authors verified that mice exposed to smoke carried similar immune cells in their lungs as do human smokers. These cells, including their secretory products IFN-γ and IL-17A, trigger the lung tissue destruction that robs emphysema patients of their ability to breathe. What activates these immune responses? The authors finger antigen-presenting cells by transferring these cells from diseased mice to healthy ones, showing that the disease transfers along with them. Then, tracing the process one step back, the authors look for smoke-induced genes in these antigen-presenting cells and identify osteopontin and Irf7, a transcription factor regulated by Spp1, as key mediators of smoke-induced cell activation. There are earlier steps in the process that have yet to be elucidated, but the cause of the havoc wreaked inside the lung by tobacco smoke is getting clearer. As a bonus, another cell type that participates in the mayhem unleashed in the emphysemic lung was uncovered. The γδ T cell, usually very rare, was unexpectedly found to be a good guy. Induced along with the destructive cells, these cells curtailed the damage but ultimately lost the battle. Perhaps bolstering the abilities of the helpful γδ T cells could ultimately help to treat serious immunogenic destructive processes in the lung. Smoking-related lung diseases are among the leading causes of death worldwide, underscoring the need to understand their pathogenesis and develop new effective therapies. We have shown that CD1a+ antigen-presenting cells (APCs) from lungs of patients with emphysema can induce autoreactive T helper 1 (TH1) and TH17 cells. Similarly, the canonical cytokines interferon-γ (IFN-γ) and interleukin-17A (IL-17A) are specifically linked to lung destruction in smokers, but how smoke activates APCs to mediate emphysema remains unknown. Here, we show that, in addition to increasing IFN-γ expression, cigarette smoke increased the expression of IL-17A in both CD4+ and γδ T cells from mouse lung. IL-17A deficiency resulted in attenuation of, whereas lack of γδ T cells exacerbated, smoke-induced emphysema in mice. Adoptive transfer of lung APCs isolated from mice with emphysema revealed that this cell population was capable of transferring disease even in the absence of active smoke exposure, a process that was dependent on IL-17A expression. Spp1 (the gene for osteopontin) was highly expressed in the pathogenic lung APCs of smoke-exposed mice and was required for the TH17 responses and emphysema in vivo, in part through its inhibition of the expression of the transcription factor Irf7. Thus, the Spp1-Irf7 axis is critical for induction of pathological TH17 responses, revealing a major mechanism by which smoke activates lung APCs to induce emphysema and identifying a pathway that could be targeted for therapeutic purposes.

Divergent functions for airway epithelial matrix metalloproteinase 7 and retinoic acid in experimental asthma

The innate immune response of airway epithelial cells to airborne allergens initiates the development of T cell responses that are central to allergic inflammation. Although proteinase allergens induce the expression of interleukin 25, we show here that epithelial matrix metalloproteinase 7 (MMP7) was expressed during asthma and was required for the maximum activity of interleukin 25 in promoting the differentiation of T helper type 2 cells. Allergen-challenged Mmp7−/− mice had less airway hyper-reactivity and production of allergic inflammatory cytokines and higher expression of retinal dehydrogenase 1. Inhibition of retinal dehydrogenase 1 restored the asthma phenotype of Mmp7−/− mice and inhibited the responses of lung regulatory T cells, whereas exogenous administration of retinoic acid attenuated the asthma phenotype. Thus, MMP7 coordinates allergic lung inflammation by activating interleukin 25 while simultaneously inhibiting retinoid-dependent development of regulatory T cells.

Agonistic induction of PPARγ reverses cigarette smoke–induced emphysema

The development of emphysema in humans and mice exposed to cigarette smoke is promoted by activation of an adaptive immune response. Lung myeloid dendritic cells (mDCs) derived from cigarette smokers activate autoreactive Th1 and Th17 cells. mDC-dependent activation of T cell subsets requires expression of the SPP1 gene, which encodes osteopontin (OPN), a pleiotropic cytokine implicated in autoimmune responses. The upstream molecular events that promote SPP1 expression and activate mDCs in response to smoke remain unknown. Here, we show that peroxisome proliferator-activated receptor γ (PPARG/Pparg) expression was downregulated in mDCs of smokers with emphysema and mice exposed to chronic smoke. Conditional knockout of PPARγ in APCs using Cd11c-Cre Pparg(flox/flox) mice led to spontaneous lung inflammation and emphysema that resembled the phenotype of smoke-exposed mice. The inflammatory phenotype of Cd11c-Cre Pparg(flox/flox) mice required OPN, suggesting an antiinflammatory mechanism in which PPARγ negatively regulates Spp1 expression in the lung. A 2-month treatment with a PPARγ agonist reversed emphysema in WT mice despite continual smoke exposure. Furthermore, endogenous PPARγ agonists were reduced in the plasma of smokers with emphysema. These findings reveal a proinflammatory pathway, in which reduced PPARγ activity promotes emphysema, and suggest that targeting this pathway in smokers could prevent and reverse emphysema.

Dual Protective Mechanisms of Matrix Metalloproteinases 2 and 9 in Immune Defense against Streptococcus pneumoniae

A localized and effective innate immune response to pathogenic bacterial invasion is central to host survival. Identification of the critical local innate mediators of lung defense against such pathogens is essential for a complete understanding of the mechanism(s) underlying effective host defense. In an acute model of Streptococcus pneumoniae lung infection, deficiency in matrix metalloproteinase (MMP)2 and MMP9 (Mmp2/9−/−) conferred a survival disadvantage relative to wild-type mice treated under the same conditions. S. pneumoniae-infected Mmp2/9−/− mice recruited more polymorphonuclear leukocytes to the lung but had higher bacterial burdens. Mmp2/9−/− mice showed significantly higher levels of IL-17A, IP-10, and RANTES in the lung. Although MMP2-dependent cleavage partially inactivated IL-17A, MMP9 was critical for effective bacterial phagocytosis and reactive oxygen species generation in polymorphonuclear neutrophils. These data demonstrate critical nonredundant and protective roles for MMP2 and MMP9 in the early host immune response against S. pneumoniae infection.