IL-21R is essential for epicutaneous sensitization and allergic skin inflammation in humans and mice.

Atopic dermatitis (AD) is a common allergic inflammatory skin disease caused by a combination of intense pruritus, scratching, and epicutaneous (e.c.) sensitization with allergens. To explore the roles of IL-21 and IL-21 receptor (IL-21R) in AD, we examined skin lesions from patients with AD and used a mouse model of allergic skin inflammation. IL-21 and IL-21R expression was upregulated in acute skin lesions of AD patients and in mouse skin subjected to tape stripping, a surrogate for scratching. The importance of this finding was highlighted by the fact that both Il21r-/- mice and WT mice treated with soluble IL-21R-IgG2aFc fusion protein failed to develop skin inflammation after e.c. sensitization of tape-stripped skin. Adoptively transferred OVA-specific WT CD4+ T cells accumulated poorly in draining LNs (DLNs) of e.c. sensitized Il21r-/- mice. This was likely caused by both DC-intrinsic and nonintrinsic effects, because trafficking of skin DCs to DLNs was defective in Il21r-/- mice and, to a lesser extent, in WT mice reconstituted with Il21r-/- BM. More insight into this defect was provided by the observation that skin DCs from tape-stripped WT mice, but not Il21r-/- mice, upregulated CCR7 and migrated toward CCR7 ligands. Treatment of epidermal and dermal cells with IL-21 activated MMP2, which has been implicated in trafficking of skin DCs. These results suggest an important role for IL-21R in the mobilization of skin DCs to DLNs and the subsequent allergic response to e.c. introduced antigen.

Selective requirement for c-Myc at an early stage of V(alpha)14i NKT cell development.

Valpha14 invariant (Valpha14i) NKT cells are a subset of regulatory T cells that utilize a semi-invariant TCR to recognize glycolipids associated with monomorphic CD1d molecules. During development in the thymus, CD4(+)CD8(+) Valpha14i NKT precursors recognizing endogenous CD1d-associated glycolipids on other CD4(+)CD8(+) thymocytes are selected to undergo a maturation program involving sequential expression of CD44 and NK-related markers such as NK1.1. The molecular requirements for Valpha14i NKT cell maturation, particularly at early developmental stages, remain poorly understood. In this study, we show that CD4-Cre-mediated T cell-specific inactivation of c-Myc, a broadly expressed transcription factor with a wide range of biological activities, selectively impairs Valpha14i NKT cell development without perturbing the development of conventional T cells. In the absence of c-Myc, Valpha14i NKT cell precursors are blocked at an immature CD44(low)NK1.1(-) stage in a cell autonomous fashion. Residual c-Myc-deficient immature Valpha14i NKT cells appear to proliferate normally, cannot be rescued by transgenic expression of BCL-2, and exhibit characteristic features of immature Valpha14i NKT cells such as high levels of preformed IL-4 mRNA and the transcription factor promyelocytic leukemia zinc finger. Collectively our data identify c-Myc as a critical transcription factor that selectively acts early in Valpha14i NKT cell development to promote progression beyond the CD44(low)NK1.1(-) precursor stage.

Maintenance of peripheral tolerance through controlled tissue homing of antigen-specific T cells in K14-mOVA mice.

Immunological tolerance is crucial to avoid autoimmune and inflammatory diseases; however, the mechanisms involved are incompletely understood. To study peripheral tolerance to skin-associated Ags, we generated new transgenic mice expressing a membrane-bound form of OVA in skin under the human keratin 14 (K14) promoter (K14-mOVA mice). In contrast to other transgenic mice expressing similar self-Ags in skin, adoptive transfer of Ag-specific T cells does not induce inflammatory skin disease in our K14-mOVA mice. OVA-specific T cells transferred into K14-mOVA mice are activated in lymphoid tissues, undergo clonal expansion, and eventually acquire effector function. Importantly, these Ag-specific T cells selectively up-regulate expression of E-selectin ligand in cutaneous lymph nodes but not in mesenteric lymph nodes and spleen, demonstrating that expression of endogenous self-Ags in skin dictates imprinting of skin tissue homing in vivo. However, an additional inflammatory signal, here induced by tape stripping, is required in K14-mOVA mice to induce T cell migration to skin and development of inflammatory skin disease. Depletion of regulatory CD4(+)CD25(+) T cells did not provoke homing of transferred T cells to skin under steady-state conditions, indicating that these cells are not the key regulators for inhibiting T cell homing in K14-mOVA mice. Both skin-derived and lymph node-resident CD8alpha(+) dendritic cells are responsible for Ag presentation in vivo and induce tolerance to skin Ags, as we show by selective depletion of langerin(+) and CD11c(+) dendritic cells. Taken together, controlled skin homing of T cells is critical for the maintenance of peripheral immune tolerance to epidermal self-Ags.

Impaired immune response to vaccinia virus inoculated at the site of cutaneous allergic inflammation.

BACKGROUND: Patients with atopic dermatitis (AD) exposed to the vaccinia virus (VV) smallpox vaccine have an increased risk of developing eczema vaccinatum. OBJECTIVE: To investigate the effects of local allergic skin inflammation on vaccinia immunity. METHODS: BALB/c mice were epicutaneously sensitized with ovalbumin (OVA) to induce allergic skin inflammation or with saline control, then inoculated with an attenuated VV strain by skin scarification or intraperitoneally. After 8 days, serum IgG anti-VV and cytokine secretion by splenocytes were measured. RESULTS: Mice inoculated with VV at sites of epicutaneous sensitization with OVA, but not control mice inoculated at saline exposed sites, developed satellite pox lesions and had impaired secretion of T(H)1 cytokines in response to VV, decreased VV specific serum IgG(2a), increased VV specific serum IgG(1), and impaired upregulation of IFN-alpha, but not the cathelicidin-related antimicrobial peptide, at the infection site. The VV immune response of OVA-sensitized mice inoculated with VV at distant skin sites or intraperitoneally was normal. CONCLUSION: Local immune dysregulation at sites of allergic skin inflammation underlies the impaired T(H)1 immune response to VV introduced at these sites and the increased susceptibility to develop satellite pox lesions, a characteristic of eczema vaccinatum in patients with AD. CLINICAL IMPLICATIONS: In a mouse model of AD, inoculation of VV at inflamed skin sites is associated with increased numbers of satellite pox lesions and an abnormal immune response to the virus. This may contribute to the susceptibility of patients with AD to virus dissemination after smallpox vaccination.

c-Myc acts downstream of IL-15 in the regulation of memory CD8 T-cell homeostasis.

A subset of CD8 T cells in normal mice, expressing high levels of activation markers such as CD44, shares many properties with antigen-specific memory CD8 T cells. Homeostasis of CD44(high) CD8 T cells depends upon cytokines such as interleukin-15 (IL-15); however, the downstream signaling pathways regulating IL-15-dependent homeostatic proliferation are poorly defined. Surprisingly, we show here that haploinsufficiency of the protooncogene c-myc leads to a highly selective decrease in CD44(high) CD8 T cells in mice. Although steady-state proliferation and survival of CD44(high) CD8 T cells appeared not to be dependent on c-Myc, homeostatic proliferation of c-myc(+/-) CD44(high) CD8 T cells in lymphopenic hosts was strongly reduced, and the residual homeostatic proliferation of these cells appeared to occur independently of IL-15. Moreover, c-myc(+/-) CD44(high) CD8 T cells responded very poorly to purified IL-15 in vitro. Backcrossing of c-myc(+/-) mice to IL-15(-/-) mice revealed that the number of CD44(high) CD8 T cells decreased in an additive fashion in mice heterozygous for c-myc and IL-15. Finally homeostatic proliferation of antigen-specific memory CD44(high) CD8 T cells was also impaired in c-myc(+/-) mice. Collectively, our data identify c-Myc as a novel downstream component of the IL-15-dependent pathway controlling homeostatic proliferation of memory CD44(high) CD8 T cells.

Localized Eastern equine encephalitis in Santiago del Estero province, Argentina, without human infection

Se documenta una epizootia de encefalitis equina del este (EEE) localizada en una zona irrigada de cuatro departamentos de la Privincia de Santiago del Estero, Argentina, en 1981. La incidencia de casos equinos fue estimada en 17% con una tasa de casos fatales del 61% y una relación de infección inaparente: aparente de < ou = 2,9:1. El diagnóstico para el virus EEE fue confirmado por pruebas serológicas y no se encontró evidencia de casos por virus de las encefalitis del oeste o Venezuela. Esta es la primera epizootia circunscripta a una pequeña área geográfica que se ha definido en Argentina y la primera en que el virus EEE se ha encontrado como único arbovirus etiológico. Su reconocimiento brindo la posibilidad de buscar la infección humana, pero no se encontró clara evidencia de enfermedad o infección. Esto se atribuyó a la baja densidad de población humana rural, aunque no se descartaron otros factores ecológicos. La serología en otros animales no permitió determinar los huéspedes vertebrados y no se estudiaron los vectores por lo cual el ciclo de transmisión continúa desconocido, impidiendo especular sobre el riesgo potencial del virus EEE para el hombre en Argentina