Min Hee Oh

The Atopic March: Progression from Atopic Dermatitis to Allergic Rhinitis and Asthma

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.

Airway Exposure Levels of Lipopolysaccharide Determine Type 1 versus Type 2 Experimental Asthma

Allergic asthma is characterized by airway inflammation initiated by adaptive immune responses to aeroallergens. Recent data suggest that severe asthma may be a different form of asthma rather than an increase in asthma symptoms and that innate immune responses to LPS can modulate adaptive immune responses to allergens. In this study, we evaluated the hypothesis that airway exposure to different doses of LPS induces different form of asthma. Our study showed that neutrophilic inflammation and IFN-γ expression were higher in induced sputum from severe asthma patients than from mild to moderate asthmatics. Animal experiments indicated that allergen sensitization with low-dose LPS (0.1 μg) induced type 2 asthma phenotypes, i.e., airway hyperresponsiveness, eosinophilic inflammation, and allergen-specific IgE up-regulation. In contrast, allergen sensitization with high-dose LPS (10 μg) induced asthma phenotypes, i.e., airway hyperresponsiveness and noneosinophilic inflammation that were not developed in IFN-γ-deficient mice, but unaffected in the absence of IL-4. During the allergen sensitization period, TNF-α expression was found to be enhanced by both low- and high-dose LPS, whereas IL-12 expression was only enhanced by high-dose LPS. Interestingly, the asthma phenotypes induced by low-dose LPS, but not by high-dose LPS, were completely inhibited in TNF-α receptor-deficient mice, whereas the asthma phenotypes induced by high-dose LPS were abolished in the homozygous null mutation of the STAT4 gene. These findings suggest that airway exposure levels of LPS induces different forms of asthma that are type 1 and type 2 asthma phenotypes by high and low LPS levels, respectively.

IL-13 Induces Skin Fibrosis in Atopic Dermatitis by Thymic Stromal Lymphopoietin

Skin fibrotic remodeling is a major feature in human atopic dermatitis (AD). Inflammation and tissue fibrosis are common consequences of Th2 responses. Elevated IL-13 and thymic stromal lymphopoietin (TSLP) have been found in the AD skin lesions. Fibrocytes can be recruited to inflamed tissues to promote wound healing and fibrosis. Dermal transgenic expression of IL-13 causes an AD-like phenotype with fibrosis and increased TSLP. However, the role of TSLP in fibrotic remodeling is unknown. In this study, we investigated the role of TSLP and fibrocytes in the generation of IL-13–induced skin fibrosis. In AD lesion, cessation of IL-13 transgene expression resulted in reduced skin inflammation but with no effect on further progression of fibrosis. This was accompanied by markedly increased CD34+/procollagen 1+ fibrocytes. Furthermore, fibrocytes express TSLP receptor (TSLPR), and TSLP directly promotes PBMC-derived fibrocytes to produce collagen. Neutralization of TSLP or genetic deletion of TSLPR in IL-13 transgenic mice resulted in a significant reduction in fibrocytes and in skin fibrosis. Furthermore, reduction of fibrosis by depletion of TSLP was independent of IL-13. Interestingly, the number of fibrocytes was highly increased in the skin samples of AD patients. These data indicate that the progression of skin fibrosis in IL-13–induced AD occurs via TSLP/TSLPR-dependent but IL-13–independent novel mechanisms by promoting fibrocyte functions.

Asymmetric inheritance of mTORC1 kinase activity during division dictates CD8 + T cell differentiation

The asymmetric partitioning of fate-determining proteins has been shown to contribute to the generation of CD8+ effector and memory T cell precursors. Here we demonstrate the asymmetric partitioning of mTORC1 activity after the activation of naive CD8+ T cells. This results in the generation of two daughter T cells, one of which shows increased mTORC1 activity, increased glycolytic activity and increased expression of effector molecules. The other daughter T cell has relatively low mTORC1 activity and increased lipid metabolism, expresses increased amounts of anti-apoptotic molecules and subsequently displays enhanced long-term survival. Mechanistically, we demonstrate a link between T cell antigen receptor (TCR)-induced asymmetric expression of amino acid transporters and RagC-mediated translocation of mTOR to the lysosomes. Overall, our data provide important insight into how mTORC1-mediated metabolic reprogramming affects the fate decisions of T cells.

TRPA1-dependent pruritus in IL-13-induced chronic atopic dermatitis.

Chronic debilitating pruritus is a cardinal feature of atopic 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 this 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 healthy 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.

SHP-1 Deficient Mast Cells Are Hyperresponsive to Stimulation and Critical in Initiating Allergic Inflammation in the Lung

Phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1)-deficient mice display an allergic asthma phenotype that is largely IL-13 and STAT6 dependent. The cell types responsible for the Th2 phenotype have not been identified. We hypothesized that SHP-1 deficiency leads to mast cell dysregulation and increased production and release of mediators and Th2 cytokines, leading to the allergic asthma phenotype. We examined SHP-1 regulation of mast cell differentiation, survival, and functional responses to stimulation using bone marrow-derived mast cells from viable motheaten (mev) mice. We assessed pulmonary phenotypical changes in mev mice on the mast cell-deficient KitW-Sh genetic background. The results showed that SHP-1 deficiency led to increased differentiation and survival, but reduced proliferation, of mast cells. SHP-1–deficient mast cells produced and released increased amounts of mediators and Th2 cytokines IL-4 and -13 spontaneously and in response to H2O2, LPS, and FcεI cross-linking, involving c-Kit–dependent and –independent processes. The FcεRI signaling led to binding of SHP-1 to linker for activation of T cells 2 and enhanced linker for activation of T cells 2 phosphorylation in mev bone marrow-derived mast cells. Furthermore, the number of mast cells in the lung tissue of mev mice was increased and mast cell production and release of Th2 cytokines were distinctly increased upon FcεRI stimulation. When backcrossed to the KitW-Sh background, mev mice had markedly reduced pulmonary inflammation and Th2 cytokine production. These findings demonstrate that SHP-1 is a critical regulator of mast cell development and function and that SHP-1–deficient mast cells are able to produce increased Th2 cytokines and initiate allergic inflammatory responses in the lung.

Epicutaneous Exposure to Staphylococcal Superantigen Enterotoxin B Enhances Allergic Lung Inflammation via an IL-17A Dependent Mechanism

Atopic dermatitis (AD) is the initial step of the atopic march: the progression from AD to allergic rhinitis and asthma. There is a close association between skin barrier abnormalities and the development of AD and the atopic march. One of cardinal features of AD is that the lesional skin of the majority of AD patients is chronically colonized with Staphylococcus aureus with half isolates producing superantigen enterotoxin B (SEB). Although diverse roles of SEB in the pathogenesis and severity of AD have been recognized, whether SEB contributes to the dermal inflammation that drives lung inflammation and airway hyperresponsiveness (AHR) has not been examined. Here we show a novel role of S. aureus superantigen SEB in augmenting allergen ovalbumin (Ova) induced atopic march through an IL-17A dependent mechanism. When mice epicutaneously (EC) sensitized with allergen Ova, addition of topical SEB led to not only augmented systemic Th2 responses but also a markedly exaggerated systemic Th17/IL-17 immune environment. The ability of SEB in enhancing Th17/IL-17 was mediated through stimulating lymphocytes in spleen and draining lymph nodes to promote IL-6 production. Epicutaneous sensitization of mice with a combination of Ova and SEB significantly enhanced Ova-induced AHR and granulocytic lung inflammation than Ova allergen alone. When IL-17A was deleted genetically, the effects of SEB on augmenting lung inflammation and AHR were markedly diminished. These findings suggest that chronic heavy colonization of enterotoxin producing S. aureus in the skin of patients with atopic dermatitis may have an important role in the development of atopic march via an IL-17A dependent mechanism.

Expression of IL-22 in the Skin Causes Th2-Biased Immunity, Epidermal Barrier Dysfunction, and Pruritus via Stimulating Epithelial Th2 Cytokines and the GRP Pathway

Increased expression of Th22 cytokine IL-22 is a characteristic finding in atopic dermatitis (AD). However, the specific role of IL-22 in the pathogenesis of AD in vivo has yet to be elucidated. Consistent with observations in human AD, IL-22 was significantly increased in the AD skin of mice after epicutaneous sensitization to house dust mite allergen. Utilizing a skin-specific inducible transgenic system, we show in the present study that expression of IL-22 in the skin of mice caused an AD-like phenotype characterized by chronic pruritic dermatitis associated with Th2-biased local and systemic immune responses, downregulation of epidermal differentiation complex genes, and enhanced dermatitis upon epicutaneous allergen exposure. IL-22 potently induced the expression of gastrin-releasing peptide (GRP), a neuropeptide pruritogen, in dermal immune cells and sensory afferents and in their skin-innervating sensory neurons. IL-22 also differentially upregulated the expression of GRP receptor (GRPR) on keratinocytes of AD skin. The number of GRP+ cells in the skin correlated with the AD severity and the intensity of pruritus. IL-22 directly upregulated the expression of epithelial-derived type 2 cytokines (thymic stromal lymphopoietin and IL-33) and GRP in primary keratinocytes. Furthermore, GRP not only strongly induced thymic stromal lymphopoietin but it also increased the expression of IL-33 and GRPR synergistically with IL-22. Importantly, we found that the expression of GRP was strikingly increased in the skin of patients with AD. These results indicate that IL-22 plays important pathogenic roles in the initiation and development of AD, in part through inducing keratinocyte production of type 2 cytokines and activation of the GRP/GRPR pathway.

SHP-1 Regulation of Mast Cell Function in Allergic Inflammation and Anaphylaxis

Allergic inflammation and severe allergic reactions (anaphylaxis) are important in allergen induced diseases. Bacterial products such as lipopolysaccharide (LPS) are ubiquitous and can facilitate allergen induced Th2 immune responses. Phosphatase SHP-1 is critical in regulating immunological homeostasis and in allergen induced Th2 immune responses in the lung. However, the mechanisms underlying the initiation of allergic inflammation and allergen induced anaphylaxis are still not completely elucidated and it is unclear whether SHP-1 plays any role in LPS-induced airway inflammation and in allergen-induced anaphylaxis. In this study we tested the hypothesis that phosphatase SHP-1 plays an important role in allergic inflammation and anaphylaxis and determined whether its effects are through regulation of mast cell functions. SHP-1 deficient (mev/+ and mev/mev) and mast cell deficient (KitW-sh) mice were examined in their responses to LPS airway stimulation and to ovalbumin (OVA) allergen induced systemic anaphylaxis. Compared to wild type mice, mev/+ mice had significantly enhanced LPS induced airway inflammation and OVA induced anaphylactic responses, including hypothermia and clinical symptoms. These changes were mast cell dependent as KitW-sh mice had reduced responses whereas adoptive transfer of mast cells restored the responses. However, T and B cells were not involved and macrophages did not play a significant role in LPS induced airway inflammation. Interestingly, basophil differentiation from SHP-1 deficient bone marrow cells was significantly reduced. These findings provided evidence that through regulation of mast cell functions SHP-1 plays a critical role as a negative regulator in allergic inflammation and in allergen induced anaphylaxis. In addition, SHP-1 seems to be required for normal basophil development.

Regulation of nasal airway homeostasis and inflammation in mice by SHP-1 and Th2/Th1 signaling pathways.

Allergic rhinitis is a chronic inflammatory disease orchestrated by Th2 lymphocytes. Src homology 2 domain-containing protein tyrosine phosphatase (SHP)-1 is known to be a negative regulator in the IL-4α/STAT-6 signaling pathway of the lung. However, the role of SHP-1 enzyme and its functional relationship with Th2 and Th1 cytokines are not known in the nasal airway. In this study, we aimed to study the nasal inflammation as a result of SHP-1 deficiency in viable motheaten (mev) mice and to investigate the molecular mechanisms involved. Cytology, histology, and expression of cytokines and chemokines were analyzed to define the nature of the nasal inflammation. Targeted gene depletion of Th1 (IFN-γ) and Th2 (IL-4 and IL-13) cytokines was used to identify the critical pathways involved. Matrix metalloproteinases (MMPs) were studied to demonstrate the clearance mechanism of recruited inflammatory cells into the nasal airway. We showed here that mev mice had a spontaneous allergic rhinitis-like inflammation with eosinophilia, mucus metaplasia, up-regulation of Th2 cytokines (IL-4 and IL-13), chemokines (eotaxin), and MMPs. All of these inflammatory mediators were clearly counter-regulated by Th2 and Th1 cytokines. Deletion of IFN-γ gene induced a strong Th2-skewed inflammation with transepithelial migration of the inflammatory cells. These findings suggest that SHP-1 enzyme and Th2/Th1 paradigm may play a critical role in the maintenance of nasal immune homeostasis and in the regulation of allergic rhinitis.