Distinct behavior of human Langerhans cells and inflammatory dendritic epidermal cells at tight junctions in patients with atopic dermatitis.

BACKGROUND: The stratum corneum and tight junctions (TJs) form physical barriers in the epidermis. Dendrites of activated Langerhans cells (LCs) extend beyond the TJs to capture external antigens in mice. LCs and inflammatory dendritic epidermal cells (IDECs) are observed in the skin of patients with atopic dermatitis (AD). OBJECTIVE: We sought to investigate the characteristics of LCs and IDECs and the distribution of their antigen capture receptors in relation to TJs in normal and AD skin. METHODS: We characterized the interactions of LCs and IDECs with TJs and the expression patterns of langerin and FcεRI by using whole-mount epidermal sheets from healthy subjects and patients with AD, ichthyosis vulgaris, and psoriasis vulgaris. RESULTS: As in mouse skin, activated LCs penetrate TJs in human skin. The number of LCs with TJ penetration increased approximately 5-fold in erythematous lesional skin of patients with AD but not in nonlesional skin of patients with AD or lesions of patients with ichthyosis vulgaris or psoriasis. In contrast, IDECs localized in the lower part of the epidermis, and their dendrites extended horizontally without penetration through TJs. Although langerin accumulated on the tips of dendrites of activated LCs, FcεRI was expressed diffusely on the cell surfaces on LCs and IDECs in lesional skin from patients with AD. CONCLUSIONS: These findings highlight interesting differences between LCs and IDECs in epidermis of patients with AD, where LCs, but not IDECs, extend dendrites through the TJs, likely to capture antigens from outside the TJ barrier with a polarized distribution of langerin but not FcεRI. These behavioral differences between skin dendritic cells might reflect an important pathophysiology of AD.

Spontaneous atopic dermatitis-like symptoms in a/a ma ft/ma ft/J flaky tail mice appear early after birth.

Loss-of-function mutations in human profilaggrin gene have been identified as the cause of ichthyosis vulgaris (IV), and as a major predisposition factor for atopic dermatitis (AD). Similarly, flaky tail (a/a ma ft/ma ft/J) mice were described as a model for IV, and shown to be predisposed to eczema. The aim of this study was to correlate the flaky tail mouse phenotype with human IV and AD, in order to dissect early molecular events leading to atopic dermatitis in mice and men, suffering from filaggrin deficiency. Thus, 5-days old flaky tail pups were analyzed histologically, expression of cytokines was measured in skin and signaling pathways were investigated by protein analysis. Human biopsies of IV and AD patients were analyzed histologically and by real time PCR assays. Our data show acanthosis and hyperproliferation in flaky tail epidermis, associated with increased IL1ß and thymic stromal lymphopoietin (TSLP) expression, and Th2-polarization. Consequently, NFκB and Stat pathways were activated, and IL6 mRNA levels were increased. Further, quantitative analysis of late epidermal differentiation markers revealed increased Small proline-rich protein 2A (Sprr2a) synthesis. Th2-polarization and Sprr2a increase may result from high TSLP expression, as shown after analysis of 5-days old K14-TSLP tg mouse skin biopsies. Our findings in the flaky tail mouse correlate with data obtained from patient biopsies of AD, but not IV. We propose that proinflammatory cytokines are responsible for acanthosis in flaky tail epidermis, and together with the Th2-derived cytokines lead to morphological changes. Accordingly, the a/a ma ft/ma ft/J mouse model can be used as an appropriate model to study early AD onset associated with profilaggrin deficiency.

A homozygous frameshift mutation in the mouse Flg gene facilitates enhanced percutaneous allergen priming.

Loss-of-function mutations in the FLG (filaggrin) gene cause the semidominant keratinizing disorder ichthyosis vulgaris and convey major genetic risk for atopic dermatitis (eczema), eczema-associated asthma and other allergic phenotypes. Several low-frequency FLG null alleles occur in Europeans and Asians, with a cumulative frequency of approximately 9% in Europe. Here we report a 1-bp deletion mutation, 5303delA, analogous to common human FLG mutations, within the murine Flg gene in the spontaneous mouse mutant flaky tail (ft). We demonstrate that topical application of allergen to mice homozygous for this mutation results in cutaneous inflammatory infiltrates and enhanced cutaneous allergen priming with development of allergen-specific antibody responses. These data validate flaky tail as a useful model of filaggrin deficiency and provide experimental evidence for the hypothesis that antigen transfer through a defective epidermal barrier is a key mechanism underlying elevated IgE sensitization and initiation of cutaneous inflammation in humans with filaggrin-related atopic disease.

Ichthyosis vulgaris: novel FLG mutations in the German population and high presence of CD1a+ cells in the epidermis of the atopic subgroup.

BACKGROUND: Ichthyosis vulgaris (IV) is a genetic disorder with a prevalence of 1:250-1000 caused by filaggrin (FLG) mutations, which also predispose to atopic diseases. OBJECTIVES: To study the genotype/phenotype relationship in IV and to analyse whether the suggested skin barrier defect is associated with differences of epidermal dendritic cells. PATIENTS/METHODS: We evaluated a cohort of 26 German patients with IV, established an IV severity score and analysed epidermal ultrastructure, histology, filaggrin and CD1a antigens. Mutations were screened by restriction enzyme analysis. Particular sequencing techniques allowed the complete FLG analysis to reveal novel mutations. RESULTS: The combined null allele frequency of R501X and 2282del4 was 67.3%. Patients also showed the mutations S3247X and R2447X as well as five novel FLG mutations: 424del17 and 621del4 (profilaggrin S100 domain), 2974delGA (repeat 2), R3766X (repeat 10(1)) and E4265X (repeat 10(2)). Their combined allele frequency in controls was <0.7%. No mutation was found in one IV patient, all in all approximately 27% were heterozygous, and the majority (approximately 69%) showed two null alleles. The IV severity score and ultrastructure showed a significant correlation with genotypes. Interestingly, CD1a cell counts showed a significant difference between nonatopic and atopic IV patients both with eczema and without eczema. CONCLUSIONS: We confirm that the mutations R501X and 2282del4 represent the most frequent genetic cause in German IV patients. The novel mutations are probably population and family specific. The observed differences of CD1a cells support the hypothesis that there is a barrier defect that predisposes to atopic manifestations, possibly independent of atopic eczema.

The role of filaggrin loss-of-function mutations in atopic dermatitis.

PURPOSE OF REVIEW: To provide a comprehensive summary of recent genetic advances as they relate to the pathogenesis of atopic dermatitis. RECENT FINDINGS: Atopic dermatitis is a common inflammatory skin disease with a complex cause, resulting from an elaborate interplay between environmental, immunological and genetic factors. The disease is often the prelude to an atopic diathesis that includes asthma and other allergic diseases. The identification of mutations in the barrier protein filaggrin as conferring major susceptibility to atopic dermatitis and atopic dermatitis related asthma has reconfigured our understanding of disease mechanisms and highlights the importance of epidermal barrier disruption as a primary event in the disease. SUMMARY: In this review we highlight recent advances in our understanding of how filaggrin might influence the environmental-immune interface, impacting disease penetrance, severity and trajectory, and the implications for both research and therapeutics in this field. Focusing on the downstream biological consequences of altered filaggrin expression and the sequence of immunological and environmental triggers that ensue will provide the rationale for targeted therapeutics capable of restoring or preventing disruption of barrier function.