Davide Pennino

Th22 cells represent a distinct human T cell subset involved in epidermal immunity and remodeling

Th subsets are defined according to their production of lineage-indicating cytokines and functions. In this study, we have identified a subset of human Th cells that infiltrates the epidermis in individuals with inflammatory skin disorders and is characterized by the secretion of IL-22 and TNF-alpha, but not IFN-gamma, IL-4, or IL-17. In analogy to the Th17 subset, cells with this cytokine profile have been named the Th22 subset. Th22 clones derived from patients with psoriasis were stable in culture and exhibited a transcriptome profile clearly separate from those of Th1, Th2, and Th17 cells; it included genes encoding proteins involved in tissue remodeling, such as FGFs, and chemokines involved in angiogenesis and fibrosis. Primary human keratinocytes exposed to Th22 supernatants expressed a transcriptome response profile that included genes involved in innate immune pathways and the induction and modulation of adaptive immunity. These proinflammatory Th22 responses were synergistically dependent on IL-22 and TNF-alpha. Furthermore, Th22 supernatants enhanced wound healing in an in vitro injury model, which was exclusively dependent on IL-22. In conclusion, the human Th22 subset may represent a separate T cell subset with a distinct identity with respect to gene expression and function, present within the epidermal layer in inflammatory skin diseases. Future strategies directed against the Th22 subset may be of value in chronic inflammatory skin disorders.

IL-17 in atopic eczema: Linking allergen-specific adaptive and microbial-triggered innate immune response

BACKGROUND Patients with atopic eczema (AE) regularly experience colonization with Staphylococcus aureus that is directly correlated with the severity of eczema. Recent studies show that an impaired IL-17 immune response results in diseases associated with chronic skin infections. OBJECTIVE We sought to elucidate the effect of IL-17 on antimicrobial immune responses in AE skin. METHODS T cells infiltrating atopy patch test (APT) reactions were characterized for IL-17 secretion to varying stimuli. IL-17-dependent induction of the antimicrobial peptide human beta-defensin 2 (HBD-2) in keratinocytes was investigated. RESULTS Approximately 10% of APT-infiltrating T cells secreted IL-17 after phorbol 12-myristate 13-acetate (PMA)/ionomycin stimulation. Among these, 33% belonged to the newly characterized subtype T(H)2/IL-17. Despite the capacity to secrete IL-17, specific T-cell clones released only low amounts of IL-17 on cognate allergen stimulation, whereas IL-4, IFN-gamma, or both were efficiently induced. IL-17 secretion was not enhanced by IL-23, IL-1 beta, or IL-6 but was enhanced by the S aureus-derived superantigen staphylococcal enterotoxin B. Both healthy and AE keratinocytes upregulated HBD-2 in response to IL-17, but coexpressed IL-4/IL-13 partially inhibited this effect. In vivo, additional application of staphylococcal enterotoxin B induced IL-17 in APT reactions, whereas IL-4, IFN-gamma, and IL-10 were marginally regulated. Induced IL-17 upregulated HBD-2 in human keratinocytes in vivo. CONCLUSION IL-17-capable T cells, in particular T(H)2/IL-17 cells, infiltrate acute AE reactions. Although IL-17 secretion by specific T cells is tightly regulated, it can be triggered by bacteria-derived superantigens. The ineffective IL-17-dependent upregulation of HBD-2 in patients with AE is due to a partial inhibition by the type 2 microenvironment, which could partially explain why patients with AE do not clear S aureus.

Mutual Antagonism of T Cells Causing Psoriasis and Atopic Eczema

The simultaneous occurrence of psoriasis driven by type 1 helper T (Th1) cells and type 17 helper T (Th17) cells and atopic eczema dominated by type 2 helper T (Th2) cells is rare. Here, we describe three patients with co-occurring psoriasis and atopic eczema with an antagonistic course and distinct T-cell infiltrates in lesions from psoriasis and those from atopic eczema. Sensitized patients with psoriasis had a reaction to epicutaneous allergen challenge, with clinically and histologically verified eczema lesions containing a large number of allergen-reactive T cells. These findings support a causative role for T cells triggered by specific antigens in both psoriasis and atopic eczema. (Supported by the German Research Foundation and others.)

IL-17 amplifies human contact hypersensitivity by licensing hapten nonspecific Th1 cells to kill autologous keratinocytes

Th17 is a newly identified lineage of effector T cells involved in autoimmunity and immune responses to pathogens. We demonstrate in this study the pathogenic role of IL-17–producing CD4+ T lymphocytes in allergic contact dermatitis (ACD) to skin-applied chemicals. IL-17+ T cells infiltrate ACD reactions and predominantly distribute at the site of heavy spongiosis. Skin IL-17+ T cells were functionally and phenotypically heterogeneous: although pure Th17 prevailed in ACD skin, hapten responsiveness was restricted to Th1/IL-17 (IFN-γ+IL-17+) and Th0/IL-17 (IFN-γ+IL-17+IL-4+) fractions, and to lesser extent Th2/IL-17 cells. In the IFN-γ–dominated ACD environment, IL-17–releasing T cells affect immune function of keratinocytes by promoting CXCL8, IL-6, and HBD-2 production. In addition, compared with Th1, supernatants from Th1/IL-17 T cells were much more efficient in inducing ICAM-1 expression on keratinocytes and keratinocyte–T cell adhesiveness in vitro. As a consequence, exposure to combined IFN-γ and IL-17 rendered keratinocytes susceptible to ICAM-1–dependent Ag nonspecific T cell killing. Thus, IL-17 efficiently amplifies the allergic reaction by rendering virtually all of the T lymphocytes recruited at the site of skin inflammation capable to directly contribute to tissue damage.

IL-22 and TNF-α represent a key cytokine combination for epidermal integrity during infection with Candida albicans

T cells exercise their full impact on target cells through a combination of secreted cytokines. The recently described T helper cell subset Th22 is characterized by a combinatorial secretion of IL‐22 and TNF‐α. Here, we demonstrate that IL‐22 increases the TNF‐α‐dependent induction and secretion of several immune‐modulatory molecules such as initial complement factors C1r and C1s, antimicrobial peptides S100A7 and HBD‐2 (human β defensin 2), and antimicrobial chemokines CXCL‐9/‐10/‐11 in primary human keratinocytes. The synergism of IL‐22 and TNF‐α is transmitted intracellularly by MAP kinases and downstream by transcription factors of the AP‐1 family. The induction of innate immunity is relevant in an in vitro infection model, where keratinocytes stimulated with Th22 supernatants or recombinant IL‐22 plus TNF‐α effectively inhibit the growth of Candida albicans and maintain survival of epithelia. Accordingly, the combinatorial stimulation of keratinocytes with IL‐22 and TNF‐α most efficiently conserves the integrity of the epidermal barrier in a three‐dimensional skin infection model as compared with IFN‐γ, IL‐17, IL‐22 or TNF‐α alone. In summary, we demonstrate that IL‐22 and TNF‐α represent a potent, synergistic cytokine combination for cutaneous immunity.

Intraindividual genome expression analysis reveals a specific molecular signature of psoriasis and eczema

Signatures from patients with both psoriasis and eczema contribute to understanding disease pathogenesis and diagnosis. Discrimination That’s Skin Deep A molecular signature may be able to aid in the differential treatment of psoriasis from eczema. Quaranta et al. examined a group of individuals affected by both psoriasis and eczema and compared molecular signatures from psoriasis and eczema lesions on the same individual. This approach limited noise from interindividual variability, allowing the authors to focus on genes involved in disease pathogenesis. They found that psoriasis-specific genes involved not only immune mediators but also regulators of metabolism. In contrast, eczema-related genes included those related to the epidermal barrier and inflammasome activation. These insights provide not only new targets for disease-specific therapies but also an independently verified classifier that can be used in difficult to diagnose patients. Previous attempts to gain insight into the pathogenesis of psoriasis and eczema by comparing their molecular signatures were hampered by the high interindividual variability of those complex diseases. In patients affected by both psoriasis and nonatopic or atopic eczema simultaneously (n = 24), an intraindividual comparison of the molecular signatures of psoriasis and eczema identified genes and signaling pathways regulated in common and exclusive for each disease across all patients. Psoriasis-specific genes were important regulators of glucose and lipid metabolism, epidermal differentiation, as well as immune mediators of T helper 17 (TH17) responses, interleukin-10 (IL-10) family cytokines, and IL-36. Genes in eczema related to epidermal barrier, reduced innate immunity, increased IL-6, and a TH2 signature. Within eczema subtypes, a mutually exclusive regulation of epidermal differentiation genes was observed. Furthermore, only contact eczema was driven by inflammasome activation, apoptosis, and cellular adhesion. On the basis of this comprehensive picture of the pathogenesis of psoriasis and eczema, a disease classifier consisting of NOS2 and CCL27 was created. In an independent cohort of eczema (n = 28) and psoriasis patients (n = 25), respectively, this classifier diagnosed all patients correctly and also identified initially misdiagnosed or clinically undifferentiated patients.

Human IL-31 is induced by IL-4 and promotes TH2-driven inflammation.

BACKGROUND The pruritic cytokine IL-31 has been shown to be expressed by murine activated effector T Lymphocytes of a TH2 phenotype. Like IL-17 and IL-22, IL-31 is a tissue-signaling cytokine the receptor of which is mainly found on nonimmune cells. An overabundance of IL-31 has been shown in patients with atopic disorders, including dermatitis, as well as asthma, and therefore represents a promising drug target, although its regulation in the context of the human TH2 clusters is not yet known. OBJECTIVE We sought to address the gene regulation of human IL-31 and to test whether IL-31 possesses a similar proallergic function as members of the human TH2 cytokine family, such as IL-4, IL-5, and IL-13. METHODS Polyclonal and purified protein derivative of tuburculin-specific T-cell clones were generated. TH phenotype was determined, and IL-31 was measured by means of ELISA. Gene expression of primary bronchial epithelial cells treated with IL-31 was also measured. RESULTS IL-31 was expressed by all of the TH2 clones and not by TH1, TH17, or TH22. This expression was dependent on autocrine IL-4 expression from these clones because it could be reduced if blocking antibodies to IL-4 were present. Interestingly, TH1 clones were able to express IL-31 if IL-4 was added to culture. This IL-31 expression was transient and did not affect the phenotype of the TH1 clones. IL-31 was able to induce proinflammatory genes, such as CCL2 and granulocyte colony-stimulating factor. CONCLUSION IL-31 is not a TH2 cytokine in the classical sense but is likely to be expressed by a number of cells in an allergic situation in which IL-4 is present and possibly contribute to the allergic reaction.

IL-22 suppresses IFN-γ–mediated lung inflammation in asthmatic patients

BACKGROUND IL-22 controls tissue homeostasis by both proinflammatory and anti-inflammatory effects. However, the anti-inflammatory mechanisms of IL-22 remain poorly investigated. OBJECTIVE We sought to investigate the anti-inflammatory role for IL-22 in human asthma. METHODS T-cell lines derived from lung biopsy specimens of asthmatic patients were characterized by means of flow cytometry. Human bronchial epithelial cells from healthy and asthmatic subjects were stimulated with IL-22, IFN-γ, or the combination of both cytokines. Effects of cytokine stimulation were investigated by using whole-genome analysis, ELISA, and flow cytometry. The functional consequence of cytokine stimulation was evaluated in an in vitro wound repair model and T cell-mediated cytotoxicity experiments. In vivo cytokine expression was measured by using immunohistochemistry and Luminex assays in bronchoalveolar lavage fluid of healthy and asthmatic patients. RESULTS The current study identifies a tissue-restricted antagonistic interplay of IL-22 and the proinflammatory cytokine IFN-γ. On the one hand, IFN-γ antagonized IL-22-mediated induction of the antimicrobial peptide S100A7 and epithelial cell migration in bronchial epithelial cells. On the other hand, IL-22 decreased epithelial susceptibility to T cell-mediated cytotoxicity by inhibiting the IFN-γ-induced expression of MHC-I, MHC-II, and CD54/intercellular adhesion molecule 1 molecules. Likewise, IL-22 inhibited IFN-γ-induced secretion of the proinflammatory chemokines CCL5/RANTES and CXCL10/interferon-inducible protein 10 in vitro. Consistently, the IL-22 expression in bronchoalveolar lavage fluid of asthmatic patients inversely correlated with the expression of CCL5/RANTES and CXCL10/interferon-inducible protein 10 in vivo. CONCLUSIONS IL-22 might control the extent of IFN-γ-mediated lung inflammation and therefore play a tissue-restricted regulatory role.

CD56highCD16−CD62L− NK Cells Accumulate in Allergic Contact Dermatitis and Contribute to the Expression of Allergic Responses

Allergic contact dermatitis is a common disease caused by an exaggerated T cell-mediated immune response to skin-applied haptens. We show in this study that NK cells affect skin immune responses to haptens by releasing type 1 cytokines and inducing keratinocytes apoptosis. Immunohistochemical stainings demonstrated that NK lymphocytes constitute ∼10% of the inflammatory infiltrate mostly distributed in the superficial dermis and in the epidermis at the site of intense spongiotic changes. More than 90% of NK cells isolated from allergic contact dermatitis skin showed a CD3-CD56highCD16− phenotype by FACS analysis. In addition, they uniformly expressed NKG2A, intermediate to high levels of perforin, and the activating receptors, NKG2D, NKp44, and NKp46, but lacked NKp30 and killer Ig-related receptors. Skin NK lymphocytes displayed a CXCR3+CCR6+CCR5+ chemokine receptor asset for homing into inflamed skin, but not CD62L and CCR7 for lymph node homing. When NK cells from nickel-allergic donors were exposed in vitro to the metal, they failed to proliferate, to upregulate CD69, and to release IFN-γ, thus indicating that NK lymphocytes do not exhibit memory-like properties to haptens. However, IL-2 released by hapten-driven T lymphocytes rapidly induced the release of IFN-γ by NK cells and promoted the NK-mediated apoptosis of autologous keratinocytes in a hapten-independent manner. Our findings underline the importance of the interaction between innate and adaptive immune mechanisms for amplification of skin allergic responses to haptens and full expression of allergic contact dermatitis

Th17 and Th22 in Skin Allergy

Development of eczematous skin reactions depends on disease-specific and time-dependent recruitment of a variety of leukocytes affecting resident skin cells through cytotoxic mechanisms and release of cytokines. Th17 and Th22, defined as RORC+IL-17+ and IL-17-IFN-γ-IL-22+ cells, respectively, belong to a newly identified class of lymphocytes specifically involved in dialogue with non-immune cells. In line with this function, both Th17 and Th22 cells are enriched in many immune-mediated skin diseases, such as a topic dermatitis, allergic contact dermatitis and psoriasis. Both IL-17 and IL-22 activate keratinocyte innate immune defenses, thus protecting the skin from pathogen invasion. However, Th17 and Th22 differ in their proinflammatory functions, being prominent in the first T cell subset and occasional/opportunistic in the second T cell subset. Most of the proinflammatory functions of Th17 depend on the synergic activity of IFN-γ and IL-17 on target cells. Together with IFN-γ, IL-17 strongly enhances adhesion molecules on keratinocytes, thus promoting T cell-keratinocyte adhesion and T cell-mediated cytotoxicity, resulting in keratinocyte apoptosis. In contrast, Th22 cells guarantee skin integrity by inducing keratinocyte proliferation and migration. However, in inflamed skin, Th22 could contribute to the amplification of immune responses by enhancing the TNF-α-induced cytokines and chemokines released by keratinocytes.