Chitin is a surface component of parasites and insects, and chitinases are induced in lower life forms during infections with these agents. Although chitin itself does not exist in humans, chitinases are present in the human genome. We show here that acidic mammalian chitinase (AMCase) is induced via a T helper-2 (Th2)-specific, interleukin-13 (IL-13)-mediated pathway in epithelial cells and macrophages in an aeroallergen asthma model and expressed in exaggerated quantities in human asthma. AMCase neutralization ameliorated Th2 inflammation and airway hyperresponsiveness, in part by inhibiting IL-13 pathway activation and chemokine induction. AMCase may thus be an important mediator of IL-13-induced responses in Th2-dominated disorders such as asthma.

Cigarette smoke exposure is the major cause of chronic obstructive pulmonary disease (COPD). However, only a minority of smokers develop significant COPD, and patients with asthma or asthma-like airway hyperresponsiveness or eosinophilia experience accelerated loss of lung function after cigarette smoke exposure. Pulmonary inflammation is a characteristic feature of lungs from patients with COPD. Surprisingly, the mediators of this inflammation and their contributions to the pathogenesis and varied natural history of COPD are not well defined. Here we show that IL-13, a critical cytokine in asthma, causes emphysema with enhanced lung volumes and compliance, mucus metaplasia, and inflammation, when inducibly overexpressed in the adult murine lung. MMP-2, -9, -12, -13, and -14 and cathepsins B, S, L, H, and K were induced by IL-13 in this setting. In addition, treatment with MMP or cysteine proteinase antagonists significantly decreased the emphysema and inflammation, but not the mucus in these animals. These studies demonstrate that IL-13 is a potent stimulator of MMP and cathepsin-based proteolytic pathways in the lung. They also demonstrate that IL-13 causes emphysema via a MMP-and cathepsin-dependent mechanism(s) and highlight common mechanisms that may underlie COPD and asthma. in proteases and/or reduction in pulmonary antiproteases (1). Inflammation, characterized by increased numbers of macrophages, lymphocytes, neutrophils, and/or eosinophils is a characteristic feature of lungs from patients with COPD (1,(14)(15)(16)(17)(18)(19). However, the nature of the mediators involved in this inflammation and the ability of these mediators to generate the emphysema and mucus changes, protease/antiprotease alterations, and varied natural history of COPD have not been investigated.Because Th2-dominated inflammation underlies the pathogenesis of asthma and generates AHR and eosinophilia (20-22), we hypothesized that Th2 cytokines can also activate proteolytic pathways that could contribute to the pathogenesis of COPD. To test this hypothesis, we used an inducible overexpression transgenic modeling system to target IL-13, a Th2 cytokine that is strongly implicated in the pathogenesis of asthma and causes AHR and eosinophilia (20,23), to the adult murine lung. These studies demonstrate that IL-13 causes a phenotype that mirrors human COPD including emphysema with enhanced lung volumes and pulmonary compliance; mucus metaplasia; and macrophage-, lymphocyte-, and eosinophil-rich inflammation. They also define the MMP and cathepsin abnormalities that generate the emphysema and demonstrate the efficacy of proteolytic blockade in ameliorating this response. MethodsTransgenic mice. These experiments were undertaken with CC10-rtTA-IL-13 mice in which the Clara cell 10-kDa (CC10) protein promoter and two transgenic constructs target IL-13 to the murine lung in an externally regulatable fashion. The CC10-rtTA transgenic system and the constructs that were used have been described previously by our laboratory (24). Construct 1,...

Chronic inflammation containing CD8 ϩ lymphocytes, neutrophils, and macrophages, and pulmonary emphysema coexist in lungs from patients with chronic obstructive pulmonary disease. Although this inflammatory response is believed to cause the remodeling that is seen in these tissues, the mechanism(s) by which inflammation causes emphysema have not been defined. Here we demonstrate that interferon ␥ (IFN-␥ ), a prominent product of CD8 ϩ cells, causes emphysema with alveolar enlargement, enhanced lung volumes, enhanced pulmonary compliance, and macrophage-and neutrophil-rich inflammation when inducibly targeted, in a transgenic fashion, to the adult murine lung. Prominent protease and antiprotease alterations were also noted in these mice. They included the induction and activation of matrix metalloproteinase (MMP)-12 and cathepsins B, H, D, S, and L, the elaboration of MMP-9, and the selective inhibition of secretory leukocyte proteinase inhibitor. IFN-␥ causes emphysema and alterations in pulmonary protease/antiprotease balance when expressed in pulmonary tissues.

Lipids in the stratum corneum of atopic dermatitis (AD) patients differ substantially in composition from healthy subjects. We hypothesized that hyperactivated type 2 immune response alters AD skin lipid metabolism. We have analyzed stratum corneum lipids from nonlesional and lesional skin of AD subjects and IL-13 skin-specific Tg mice. We also directly examined the effects of IL-4/IL-13 on human keratinocytes in vitro. Mass spectrometric analysis of lesional stratum corneum from AD subjects and IL-13 Tg mice revealed an increased proportion of short-chain (N-14:0 to N-24:0) NS ceramides, sphingomyelins, and 14:0-22:0 lysophosphatidylcholines (14:0-22:0 LPC) with a simultaneous decline in the proportion of corresponding long-chain species (N-26:0 to N-32:0 sphingolipids and 24:0-30:0 LPC) when compared with healthy controls. An increase in short-chain LPC species was also observed in nonlesional AD skin. Similar changes were observed in IL-4/IL-13-driven responses in Ca2+-differentiated human keratinocytes in vitro, all being blocked by STAT6 silencing with siRNA. RNA sequencing analysis performed on stratum corneum of AD as compared with healthy subjects identified decreased expression of fatty acid elongases ELOVL3 and ELOVL6 that contributed to observed changes in atopic skin lipids. IL-4/IL-13 also inhibited ELOVL3 and ELOVL6 expression in keratinocyte cultures in a STAT6-dependent manner. Downregulation of ELOVL3/ELOVL6 expression in keratinocytes by siRNA decreased the proportion of long-chain fatty acids globally and in sphingolipids. Thus, our data strongly support the pathogenic role of type 2 immune activation in AD skin lipid metabolism.

Atopic dermatitis (AD) is an inflammatory disease characterized by pruritic skin lesions. The pathogenesis of AD may include disrupted epidermal barrier function, immunodysregulation, and IgE-mediated sensitization to food and environmental allergens. AD is also part of a process called the atopic march, a progression from AD to allergic rhinitis and asthma. This has been supported by multiple cross-sectional and longitudinal studies and experimental data. Research on the mechanisms of AD has been centered on the adaptive immune system with an emphasis on the T-helper 1 (Th1)-Th2 paradigm. Recently, the conceptual focus has largely shifted to include a primary defect in the epithelial barrier as an initial event in AD providing a significant insight into the disease initiation and pointing to a complex secondary interplay of environmental and immunological sequelae with barrier disruption. Further understanding of AD will help the development of more effective treatment for AD and ultimately, preventative algorithms for the atopic march. In this review we highlight recent advances in our understanding of the pathogenesis of AD and the atopic march.

The development of atopic dermatitis (AD) in infancy and subsequent allergic rhinitis and asthma in later childhood is known as the atopic march. This progressive atopy is dependent on various underlying factors such as the presence of filaggrin mutations as well as the time of onset and severity of AD. Clinical manifestations vary among individuals. Previously it was thought that atopic disorders may be unrelated with sequential development. Recent studies support the idea of a causal link between AD and later onset atopic disorders. These studies suggest that a dysfunctional skin barrier serves as a site for allergic sensitization to antigens and colonization of bacterial super antigens. This induces systemic Th2 immunity that predisposes patients to allergic nasal responses and promotes airway hyper reactivity. While AD often starts early in life and is a chronic condition, new research signifies that there may be an optimal window of time in which targeting the skin barrier with therapeutic interventions may prevent subsequent atopic disorders. In this review we highlight recent studies describing factors important in the development of atopic disorders and new insights in our understanding of the pathogenesis of the atopic march.

IL-13 stimulates inflammatory and remodeling responses and contributes to the pathogenesis of human airways disorders. To further understand the cellular and molecular events that mediate these responses, we characterized the effects of IL-13 on monocyte chemotactic proteins (MCPs) and compared the tissue effects of transgenic IL-13 in mice with wild-type (+/+) and null (−/−) CCR2 loci. Transgenic IL-13 was a potent stimulator of MCP-1, -2, -3, and -5. This stimulation was not specific for MCPs because macrophage-inflammatory protein (MIP)-1α, MIP-1β, MIP-2, MIP-3α, thymus- and activation-regulated chemokine, thymus-expressed chemokine, eotaxin, eotaxin 2, macrophage-derived chemokines, and C10 were also induced. The ability of IL-13 to increase lung size, alveolar size, and lung compliance, to stimulate pulmonary inflammation, hyaluronic acid accumulation, and tissue fibrosis, and to cause respiratory failure and death were markedly decreased, whereas mucus metaplasia was not altered in CCR2−/− mice. CCR2 deficiency did not decrease the basal or IL-13-stimulated expression of target matrix metalloproteinases or cathepsins but did increase the levels of mRNA encoding α1-antitrypsin, tissue inhibitor of metalloproteinase-1, -2, and -4, and secretory leukocyte proteinase inhibitor. In addition, the levels of bioactive and total TGF-β1 were decreased in lavage fluids from IL-13 transgenic mice with −/− CCR2 loci. These studies demonstrate that IL-13 is a potent stimulator of MCPs and other CC chemokines and document the importance of MCP-CCR2 signaling in the pathogenesis of the IL-13-induced pulmonary phenotype.

Chronic debilitating pruritus is a cardinal feature of a topic dermatitis (AD). Little is known about the underlying mechanisms. Antihistamines lack efficacy in treating itch in AD, suggesting the existence of histamine-independent itch pathways in AD. Transient receptor potential ankyrin 1 (TRPA1) is essential in the signaling pathways that promote histamine-independent itch. In the present study, we tested the hypothesis that TRPA1-dependent neural pathways play a key role in chronic itch in AD using an IL-13 transgenic mouse model of AD. In these mice, IL-13 causes chronic AD characterized by intensive chronic itch associated with markedly enhanced growth of dermal neuropeptide-secreting afferent nerve fibers and enhanced expression of TRPA1 in dermal sensory nerve fibers, their dorsal root ganglia, and mast cells. Inhibition of TRPA1 with a specific antagonist in these mice selectively attenuated itch-evoked scratching. Genetic deletion of mast cells in these mice led to significantly diminished itch-scratching behaviors and reduced TRPA1 expression in dermal neuropeptide containing afferents in the AD skin. Interestingly, IL-13 strongly stimulates TRPA1 expression, which is functional in calcium mobilization in mast cells. In accordance with these observations in the AD mice, TRPA1 expression was highly enhanced in the dermal afferent nerves, mast cells, and the epidermis in the lesional skin biopsies from patients with AD, but not in the skin from normal subjects. These studies demonstrate a novel neural mechanism underlying chronic itch in AD and highlight the complex interactions among TRPA1+ dermal afferent nerves and TRPA1+ mast cells in a Th2-dominated inflammatory environment.