In vitro and in situ expression of IL-23 by keratinocytes in healthy skin and psoriasis lesions: enhanced expression in psoriatic skin

Keratinocytes contribute to cutaneous immune responses through the expression of cytokines. We investigated whether human keratinocytes can express IL-23, a newly defined IFN-gamma-inducing cytokine composed of a unique p19 subunit and a p40 subunit shared with IL-12. Cultured keratinocytes from normal and lesional psoriatic skin were found to express constitutively mRNA for both subunits of IL-23. Low but significant levels of the heterodimeric IL-23 protein could be detected in cell lysates and supernatants from stimulated keratinocytes by immunoblotting and ELISA. Functional analysis showed that these low levels of keratinocyte-derived IL-23 were sufficient to enhance the IFN-gamma production by memory T cells. Immunostaining of skin sections confirmed expression of both subunits of IL-23 by keratinocytes in situ and also revealed expression of this cytokine in the dermal compartment. IL-23 expression was significantly higher in psoriatic lesional skin, compared with normal and psoriatic nonlesional skin. The immunostained preparations of cultured cells and IL-23 levels in culture supernatants did not show any difference between normal and psoriatic keratinocytes indicating no intrinsic aberration of IL-23 expression in keratinocytes from psoriatic skin. Double staining of cytospin preparations demonstrated that IL-23 p19 is also expressed by epidermal Langerhans cells, dermal dendritic cells, and macrophages. Psoriasis is a chronic inflammatory skin disease mediated by IFN-gamma-expressing type 1 memory T cells. As IL-23 is important to activate memory T cells to produce IFN-gamma, its augmented expression of IL-23 by keratinocytes and cutaneous APC may contribute to the perpetuation of the inflammation process in this disease.     

IL-12 and IL-18 are increased and stimulate IFN-gamma production in sarcoid lungs

Sarcoidosis is a systemic chronic granulomatous disease of unknown cause. Recent investigations revealed that the cytokine profile in inflamed lesions of sarcoidosis is Th1 dominant. To obtain better immunopathologic understanding of sarcoidosis, we examined the expression of IL-12 and IL-18 and their roles in IFN-gamma production in pulmonary sarcoidosis. Sarcoid cases had significantly elevated levels of IL-12 (p40 and p70) and IL-18 in bronchoalveolar lavage (BAL) fluids compared with healthy subjects. IL-12 p70 and IL-18 were immunohistochemically expressed in the epithelioid cells and giant cells of sarcoid granulomas. Significant induction of IFN-gamma, IL-12 p70, and IL-18 was observed from sarcoid BAL fluid cells with LPS stimulation, whereas LPS tended to induce only IL-12 p70 in BAL fluid cells from healthy subjects. Sarcoid cases had significantly greater IFN-gamma induction with LPS stimulation than healthy subjects did. IL-18 mRNA expression was observed in freshly isolated sarcoid BAL fluid cells as well as in LPS-stimulated sarcoid BAL fluid cells, but IFN-gamma and IL-12 mRNA expression was observed only in LPS-stimulated BAL fluid cells. Treatment with anti-IL-12- and anti-IL-18-neutralizing Abs significantly inhibited IFN-gamma production from LPS-stimulated BAL fluid cells of sarcoid cases. Coadministration of rIL-12 or rIL-18 induced greater IFN-gamma production in sarcoid BAL fluid cells than in normal BAL fluid cells. We concluded that bioactive IL-12 and IL-18 were produced in sarcoid BAL fluid cells and synergistically induced IFN-gamma production, indicating important cytokines in the Th1 response of sarcoidosis.     

Human keratinocytes are major producers of IL-18: predominant expression of the unprocessed form

The cytokine network in the skin is a tightly regulated system in which IL-1 isoforms, as well as their receptors and antagonists have a central role. The recently discovered IL-1 isoform IL-18 (also known as interferon gamma-inducing factor (IGIF) or IL-1gamma), promotes IFN-gamma expression by T cells in concert with IL-12. Because IFN-gamma plays an important role in many inflammatory skin diseases by facilitating the development of Th1 cells, it is important to elucidate the role of mediators which regulate the production of this cytokine. We demonstrate that human keratinocytes constitutively express IL-18 at the mRNA as well as at the protein level. The protein was mainly expressed intracellularly in the 24 kD unprocessed pro-form, but was also secreted. Histochemistry revealed a diffuse staining of IL-18 in the epidermis of normal skin, which is in line with our in vitro data. Furthermore, we show that the level of IL-18 expressed in freshly isolated normal human epidermal cells, whether or not containing HLA-DR+ cells, significantly exceeded the expression levels of other cell types such as monocytes and bronchial epithelial cells. Finally, our results show that stimulation of the keratinocyte cell line HaCaT with PMA LPS or IL-1beta, does not significantly affect intracellular or released (pro) IL-18 levels. These experiments show for the first time that human keratinocytes relative to monocytes, PBMC or leukocytes produce a considerably larger amount of pro-IL-18, which is also readily released. High constitutive levels of IL-18 may contribute to the skewing towards a Th1-like environment, which is apparent in many human inflammatory skin diseases.     

Induction of IL-17+ T cell trafficking and development by IFN-gamma: mechanism and pathological relevance in psoriasis

Th1 and Th17 T cells are often colocalized in pathological environments, yet Th1-derived IFN-gamma inhibits Th17 cell development in vitro. We explored the physiologic basis of this paradox in humans. In this study, we demonstrate increased the number of CD4(+) and CD8(+) IL-17(+) T cells in skin lesions of psoriasis. Furthermore, we show that myeloid APCs potently support induction of IL-17(+) T cells, and that this activity is greatly increased in psoriasis. We tested stimuli that might account for this activity. Th1 cells and IFN-gamma are increased in psoriatic blood and lesional skin. We show that IFN-gamma programs myeloid APCs to induce human IL-17(+) T cells via IL-1 and IL-23. IFN-gamma also stimulates APC production of CCL20, supporting migration of IL-17(+) T cells, and synergizes with IL-17 in the production of human beta-defensin 2, an antimicrobial and chemotactic protein highly overexpressed by psoriatic keratinocytes. This study reveals a novel mechanistic interaction between Th1 and IL-17(+) T cells, challenges the view that Th1 cells suppress Th17 development through IFN-gamma, and suggests that Th1 and IL-17(+) T cells may collaboratively contribute to human autoimmune diseases.     

Complete regression of established spontaneous mammary carcinoma and the therapeutic prevention of genetically programmed neoplastic transition by IL-12/pulse IL-2: induction of local T cell infiltration, Fas/Fas ligand gene expression, and mammary epithelial apoptosis

Using a novel transgenic mouse model of spontaneous mammary carcinoma, we show here that the IL-12/pulse IL-2 combination can induce rapid and complete regression of well-established autochthonous tumor in a setting where the host immune system has been conditioned by the full dynamic process of neoplastic progression and tumorigenesis. Further, this regimen inhibits neovascularization of established mammary tumors, and does so in conjunction with potent local induction of genes encoding the IFN-gamma- and TNF-alpha-inducible antiangiogenic chemokines IFN-inducible protein 10 and monokine induced by IFN-gamma. In contrast to untreated juvenile C3(1)TAg mice in which histologically normal mammary epithelium predictably undergoes progressive hyperplasia, atypical changes, and ultimately transition to overt carcinoma, the current studies also demonstrate a unique preventative therapeutic role for IL-12/pulse IL-2. In juvenile mice, early administration of IL-12/pulse IL-2 markedly limits the expected genetically programmed neoplastic transition within the mammary epithelium and does so in conjunction with enhancement of constitutive Fas and pronounced induction of local Fas ligand gene expression, T cell infiltration, and induction of apoptosis within the mammary epithelium. These events occur in the absence of a durable Ag-specific memory response. Thus, this novel model system demonstrates that the potent therapeutic activity of the IL-12/pulse IL-2 combination rapidly engages potent apoptotic and antiangiogenic mechanisms that remain active during the delivery of IL-12/pulse IL-2. The results also demonstrate that these mechanisms are active against established tumor as well as developing preneoplastic lesions.     

IL-21 promotes skin recruitment of CD4(+) cells and drives IFN-γ-dependent epidermal hyperplasia

Psoriasis is a chronic inflammatory disorder of the skin characterized by epidermal hyperplasia and infiltration of leukocytes into the dermis and epidermis. T cell-derived cytokines, such as IFN-γ and IL-17A, play a major role in the psoriasis-associated epidermal hyperplasia, even though factors/mechanisms that regulate the production of these cytokines are not fully understood. We have recently shown that IL-21 is synthesized in excess in psoriatic skin lesions and causes epidermal hyperplasia when injected intradermally in mice. Moreover, in the human psoriasis SCID mouse model, neutralization of IL-21 reduces both skin thickening and expression of inflammatory molecules, thus supporting the pathogenic role of IL-21 in psoriasis. However, the basic mechanism by which IL-21 promotes skin pathology remains unknown. In this study, we show that CD4(+) cells accumulate early in the dermis of IL-21-treated mice and mediate the development of epidermal hyperplasia. Indeed, IL-21 fails to induce skin damage in RAG1-deficient mice and CD4(+) cell-depleted wild-type mice. The majority of CD4(+) cells infiltrating the dermis of IL-21-treated mice express IFN-γ and, to a lesser extent, IL-17A. Studies in cytokine knockout mice show that IFN-γ, but not IL-17A, is necessary for IL-21-induced epidermal hyperplasia. Finally, we demonstrate that IFN-γ-producing CD4(+) cells infiltrating the human psoriatic plaque express IL-21R, and abrogation of IL-21 signals reduces IFN-γ expression in cultures of psoriatic CD4(+) cells. Data indicate that IL-21 induces an IFN-γ-dependent pathogenic response in vivo, thus contributing to elucidate a mechanism by which IL-21 sustains skin-damaging inflammation.     

IL-12 induces monocyte IL-18 binding protein expression via IFN-gamma

IL-18 is a Th1 cytokine that synergizes with IL-12 and IL-2 in the stimulation of lymphocyte IFN-gamma production. IL-18 binding protein (IL-18BP) is a recently discovered inhibitor of IL-18 that is distinct from the IL-1 and IL-18 receptor families. In this report we show that IL-18BPa, the IL-18BP isoform with the highest affinity for IL-18, was strongly induced by IL-12 in human PBMC. Other Th1 cytokines, including IFN-gamma, IL-2, IL-15, and IL-18, were also capable of augmenting IL-18BPa expression. In contrast, IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma-inducible protein-10, and Th2 cytokines such as IL-4 and IL-10 did not induce IL-18BPa. Although monocytes were found to be the primary source of IL-18BPa, the induction of IL-18BPa by IL-12 was mediated through IFN-gamma derived predominantly from NK cells. IL-18BPa production was observed in cancer patients receiving recombinant human IL-12 and correlated with the magnitude of IFN-gamma production. The IFN-gamma/IL-18BPa negative feedback loop identified in this study may be capable of broadly controlling immune activation by cytokines that synergize with IL-18 to induce IFN-gamma and probably plays a key role in the modulation of both innate and adaptive immunity.     

Overexpression of CD1d by keratinocytes in psoriasis and CD1d-dependent IFN-gamma production by NK-T cells

The MHC class I-like protein CD1d is a nonpolymorphic molecule that plays a central role in development and activation of a subset of T cells that coexpress receptors used by NK cells (NK-T cells). Recently, T cells bearing NK receptors were identified in acute and chronic lesions of psoriasis. To determine whether NK-T cells could interact with epidermal cells, we examined the pattern of expression of CD1d in normal skin, psoriasis, and related skin disorders, using a panel of CD1d-specific mAbs. CD1d was expressed by keratinocytes in normal skin, although expression was at a relatively low level and was generally confined to upper level keratinocytes immediately beneath the lipid-rich stratum corneum. In contrast, there was overexpression of CD1d in chronic, active psoriatic plaques. CD1d could be rapidly induced on keratinocytes in normal skin by physical trauma that disrupted barrier function or by application of a potent contact-sensitizing agent. Keratinocytes displayed enhanced CD1d following exposure to IFN-gamma. Combining CD1d-positive keratinocytes with human NK-T cell clones resulted in clustering of NK-T cells, and while no significant proliferation ensued, NK-T cells became activated to produce large amounts of IFN-gamma. We conclude that CD1d can be expressed in a functionally active form by keratinocytes and is up-regulated in psoriasis and other inflammatory dermatoses. The ability of IFN-gamma to enhance keratinocyte CD1d expression and the subsequent ability of CD1d-positive keratinocytes to activate NK-T cells to produce IFN-gamma, could provide a mechanism that contributes to the pathogenesis of psoriasis and other skin disorders.     

Neutrophil chemoattractant and IL-1-like activity in samples from psoriatic skin lesions. Further characterization

The IL-1-like neutrophil chemoattractant activity previously reported by us to be present in the stratum corneum of psoriatic skin lesions has now been characterized further. Aqueous extracts of stratum corneum samples from psoriatic lesions and from the heels of normal volunteers were ultrafiltered to yield 10- to 30-kDa fractions. The ultrafiltered psoriatic preparations consistently contained greater neutrophil chemokinetic activity than the normal heel preparations, but in contrast the latter contained markedly greater IL-1 activity than the former. Successive chromatographic purification of psoriatic lesional stratum corneum extracts showed that the neutrophil chemokinetic material previously reported to co-elute with IL-1 activity on reversed phase HPLC, but to be distinct from C5a des arg, could now be separated by anion exchange HPLC into at least four different chemokinetic compounds that were also resolved from the IL-1 activity. The reversed phase HPLC-purified chemokinetic material from psoriatic stratum corneum was also active in a neutrophil chemotaxis assay. These findings show that samples from psoriatic skin lesions contain a group of novel 10- to 30-kDa neutrophil chemoattractant compounds that are distinct from both C5a des arg and IL-1. The contrasting neutrophil chemokinetic and IL-1 activities in psoriatic lesional and normal heel stratum corneum preparations support the finding that the two activities are produced by different compounds. These neutrophil chemoattractant and IL-1-like compounds may be of pathogenic importance in inflammatory skin disease.     

Lack of interferon-gamma production despite the presence of interleukin-18 during cutaneous wound healing

BACKGROUND: Recently, we have reported a rapid and strong induction of interleukin-18 (IL-18) upon cutaneous injury in mice. In this paper, we investigated a possible role of IL-18 in triggering interferon-gamma (IFN-gamma) production at the wound site. MATERIALS AND METHODS: Expression of IFN-gamma during cutaneous wound healing was analyzed by RNase protection assay, Western blot, ELISA, and immunohistochemical techniques in a murine model of excisional skin repair. RESULTS: We could not detect any IFN-gamma mRNA and protein expression during normal skin repair. Additionally, impaired healing in the genetically diabetic db/db mouse, which was used as a model for a prolonged inflammatory phase of repair, was characterized by largely elevated levels of IL-18 during the late phase of repair and an absence of IFN-gamma. Western blot analysis for T-cell- and monocyte/macrophage-specific marker proteins (CD4, F4/80) clearly revealed the presence of these subsets of leukocytic cells at the wound site, that are known to produce IFN-gamma in response to IL-18. Furthermore, we provide evidence that the presence of transforming growth factor-beta1 (TGF-beta1) at the wound site might reflect a counterregulatory mechanism in IL-18-induced IFN-gamma production, as TGF-beta1 strongly suppressed IL-18/phytohaemagglutinin (PHA)-induced IFN-gamma production by peripheral blood mononuclear cells (PBMC) in vitro. CONCLUSIONS: Normal tissue regeneration processes after cutaneous injury were not dependent on the presence of IFN-gamma in vivo, and IL-18 must serve additional roles rather than inducing IFN-gamma during the healing process.     

IL-18 is a potent coinducer of IL-13 in NK and T cells: a new potential role for IL-18 in modulating the immune response

IL-13 and IL-4 have similar biological activities and are characteristic of cytokines expressed by Th2 cells. In contrast, IL-12 and IL-18 have been shown to be strong cofactors for Th1 cell development. In this study, we found strong induction of IL-13 mRNA and protein by IL-2 + IL-18 in NK and T cells. In contrast, IL-12 did not enhance the IL-13 production induced by IL-2 alone. Moreover, IL-13 mRNA and protein expression induced by IL-2 + IL-18 in purified NK and T cells obtained from IFN-gamma knockout (-/-) mice were greater than seen in purified cells from normal controls. In contrast, IL-10 production induced by IL-2 and/or IL-12 was not significantly different in IFN-gamma (-/-) mice and normal controls. These results suggest IL-13 expression induced by IL-2 + IL-18 may be regulated by IFN-gamma in vivo, while IL-10 expression may be IFN-gamma-independent. Thus, depending upon the cell type, IL-18 may act as a strong coinducer of Th1 or Th2 cytokines. Our findings suggest that IL-12 and IL-18 have different roles in the regulation of gene expression in NK and T cells.     

IL-21 in synergy with IL-15 or IL-18 enhances IFN-gamma production in human NK and T cells

NK and T cell-derived IFN-gamma is a key cytokine that stimulates innate immune responses and directs adaptive T cell response toward Th1 type. IL-15, IL-18, and IL-21 have significant roles as activators of NK and T cell functions. We have previously shown that IL-15 and IL-21 induce the expression of IFN-gamma, T-bet, IL-12R beta 2, and IL-18R genes both in NK and T cells. Now we have studied the effect of IL-15, IL-18, and IL-21 on IFN-gamma gene expression in more detail in human NK and T cells. IL-15 clearly activated IFN-gamma mRNA expression and protein production in both cell types. IL-18 and IL-21 enhanced IL-15-induced IFN-gamma gene expression. IL-18 or IL-21 alone induced a modest expression of the IFN-gamma gene but a combination of IL-21 and IL-18 efficiently up-regulated IFN-gamma production. We also show that IL-15 activated the binding of STAT1, STAT3, STAT4, and STAT5 to the regulatory sites of the IFN-gamma gene. Similarly, IL-21 induced the binding of STAT1, STAT3, and STAT4 to these elements. IL-15- and IL-21-induced STAT1 and STAT4 activation was verified by immunoprecipitation with anti-phosphotyrosine Abs followed by Western blotting with anti-STAT1 and anti-STAT4 Abs. IL-18 was not able to induce the binding of STATs to IFN-gamma gene regulatory sites. IL-18, however, activated the binding of NF-kappa B to the IFN-gamma promoter NF-kappa B site. Our results suggest that both IL-15 and IL-21 have an important role in activating the NK cell-associated innate immune response.     

Stat4 regulates multiple components of IFN-gamma-inducing signaling pathways

Stat4 is activated in response to IL-12. Most functions of IL-12, including the induction of IFN-gamma, are compromised in the absence of Stat4. Since the precise role of Stat4 in IFN-gamma induction has not been established, experiments were conducted to examine Stat4 activation of IFN-gamma and other genes required for cytokine-induced expression of IFN-gamma. We first examined IL-12 signaling components. Basal expression of IL-12Rss1 and IL-12Rss2 is decreased in Stat4-deficient cells compared with that in control cells. However, IL-12 was still capable of inducing equivalent phosphorylation of Jak2 and Tyk2 in wild-type and Stat4-deficient activated T cells. We have further determined that other cytokine signaling pathways that induce IFN-gamma production are defective in the absence of Stat4. IL-18 induces minimal IFN-gamma production from Stat4-deficient activated T cells compared with control cells. This is due to defective IL-18 signaling, which results from the lack of IL-12-induced, and Stat4-dependent, expression of the IL-18R. Following IL-12 pretreatment to induce IL-18R, wild-type, but not Stat4-deficient, activated T cells demonstrated IL-18-induced NF-kappaB DNA-binding activity. In addition, IL-12-pretreated Stat4-deficient activated T cells have minimal IFN-gamma production followed by stimulation with IL-18 alone or in combination with IL-12 compared with control cells. Thus, Stat4 activation by IL-12 is required for the function of multiple cytokine pathways that result in induction of IFN-gamma.     

Cytokines in skin lesions of psoriasis

Cytokine levels were compared in aqueous extracts of stratum corneum from psoriatic lesions and normal heel. Samples from heel contained high levels of interleukin-1 alpha (IL-1 alpha) and beta measured in immunoassays, although only the IL-1 alpha was biologically active. No other cytokines could be detected in heel samples. Interleukin-1 (IL-1) levels were dramatically reduced in lesional samples. A neutrophil chemoattractant was found in all lesional extracts, and was demonstrated to be mainly interleukin-8 (IL-8) using a specific neutralizing antiserum. Tumor necrosis factor alpha (TNF-alpha) and beta (TNF-beta), and interferon alpha (IFN-alpha) and gamma (IFN-gamma) were detected in lesional extracts using immunoassays, however, no equivalent biological activities could be detected. Interleukins 2 (IL-2), 4 (IL-4), and 6 (IL-6), granulocyte and granulocyte/macrophage colony stimulating factor (GM-CSF), could not be detected in any samples. IL-8 is therefore the only biologically active cytokine shown in this study to be elevated in psoriatic lesional extracts, and may therefore play a role in the pathogenesis of the disease.     

Significantly increased CCL5/RANTES and CCR7 mRNA levels in localized scleroderma

Plaque-type morphea, the most common subtype of localized scleroderma (LS), is a connective tissue disease which is characterized by immunological dysregulation, vascular alterations, and skin fibrosis. We aimed to investigate the expression profiles of different cytokines and chemokines in patients with LS and healthy controls. Twenty patients with plaque-type morphea and 18 healthy controls were investigated. Skin biopsies were performed for real-time RT-PCR studies. Median mRNA of interleukin (IL)-6 was significantly higher expressed in LS than in normal skin. By contrast, median IL-1α mRNA levels were significantly decreased in LS as compared to controls. Median mRNA expression of CCL13, IL-1β, IL-2, and tumor necrosis factor-α did not significantly differ between LS lesions and healthy skin. However, we observed significantly increased median chemokine ligand 5/RANTES (CCL5/RANTES) and median chemokine receptor 7 (CCR7) mRNA expression in LS lesions as compared to healthy controls. CCL5/RANTES and CCR7 mRNA expression significantly correlated in LS lesions. We could confirm data of previous studies indicating that gene expression of IL-6 is up-regulated in LS lesions as compared to healthy skin. Moreover, we have shown for the first time a significant increase of mRNA levels of CCR7 and CCL5/RANTES in LS lesions indicating an important pathogenetic role of chemokines in LS.     

Expression of genes for metalloproteinases (MMP-1, MMP-2, MMP-9, and MMP-12) associated with psoriasis

Using real-time polymerase chain reaction (RT-PCR), we measured mRNA amounts of matrix metalloproteinases (MMPs): MMP-1, MMP-2, MMP-9, and MMP-12 genes in psoriatic lesions and unaffected skin of the same patients. We observed significant (about 15-fold) increase in the expression level of matrix metalloproteinase MMP-1 and MMP-12 genes associated with psoriasis. The results of our studies of MMP gene expression in cultured primary human keratinocytes treated with interleukin (IL-17) have shown upregulation of MMP gene expression both in cultured keratinocytes and in psoriatic skin lesions. Therefore, upregulation of MMP genes in the skin affected by psoriasis could result from IL-17 effects on skin cells.