An IL-17-dominant immune profile is shared across the major orphan forms of ichthyosis

Abstract

Background: The ichthyoses are rare genetic disorders associated with generalized scaling, erythema, and epidermal barrier impairment. Pathogenesis-based therapy is largely lacking because the underlying molecular basis is poorly understood.

Objective: We sought to characterize molecularly cutaneous inflammation and its correlation with clinical and barrier characteristics.

Methods: We analyzed biopsy specimens from 21 genotyped patients with ichthyosis (congenital ichthyosiform erythroderma, n = 6; lamellar ichthyosis, n = 7; epidermolytic ichthyosis, n = 5; and Netherton syndrome, n = 3) using immunohistochemistry and RT-PCR and compared them with specimens from healthy control subjects, patients with atopic dermatitis (AD), and patients with psoriasis. Clinical measures included the Ichthyosis Area Severity Index (IASI), which integrates erythema (IASI-E) and scaling (IASI-S); transepidermal water loss; and pruritus.

Results: Ichthyosis samples showed increased epidermal hyperplasia (increased thickness and keratin 16 expression) and T-cell and dendritic cell infiltrates. Increases of general inflammatory (IL-2), innate (IL-1β), and some T_H1/interferon (IFN-γ) markers in patients with ichthyosis were comparable with those in patients with psoriasis or AD. TNF-α levels in patients with ichthyosis were increased only in those with Netherton syndrome but were much lower than in patients with psoriasis and those with AD. Expression of T_H2 cytokines (IL-13 and IL-31) was similar to that seen in control subjects. The striking induction of IL-17-related genes or markers synergistically induced by IL-17 and TNF-α (IL-17A/C, IL-19, CXCL1, PI3, CCL20, and IL36G; P < .05) in patients with ichthyosis was similar to that seen in patients with psoriasis. IASI and IASI-E scores strongly correlated with IL-17A (r = 0.74, P < .001) and IL-17/TNF-synergistic/additive gene expression. These markers also significantly correlated with transepidermal water loss, suggesting a link between the barrier defect and inflammation in patients with ichthyosis.

Conclusion: Our data associate a shared T_H17/IL-23 immune fingerprint with the major orphan forms of ichthyosis and raise the possibility of IL-17-targeting strategies.

Keywords: Epidermis; IL-17; Netherton syndrome; TNF-α; autosomal recessive congenital ichthyosis; congenital ichthyosiform erythroderma; epidermolytic ichthyosis; ichthyosis; inflammation; lamellar ichthyosis; skin.

Figure 1.

Representative clinical pictures of the collodion-baby phenotype (A), lamellar ichthyosis/LI (B), congenital ichthyosis erythroderma/CIE (C), epidermolytic ichthyosis/EI (D), and Netherton syndrome/NS (E-F). They share varying degrees of erythema and scaling, as in two common inflammatory skin diseases, atopic dermatitis/AD (G) and psoriasis (H). (I-M) Clinical severity scores by subtypes of ichthyosis. +p<0.1, *p<0.05, **p<0.01.

Figure 2.

Representative staining in ichthyoses, AD, psoriasis/PSO and controls using (A) hematoxylin-eosin/H&E, (B) K16 with fractions of positive samples, (C) CD3⁺ T-cells, (D) CD11c⁺ DC, and (E) filaggrin/FLG. Quantification of (F) epidermal thickness, (G) K16 mRNA, (H-I) CD3⁺ and CD11c⁺ cells and (J) filaggrin/FLG mRNA. mRNA-log₂ values were adjusted to hARP. Mean±SEM. Controls comparisons: stars above bars. *p<0.05, **p<0.01, ***p<0.001. LS: lesional; NL: non-lesional.

Figure 3.

Comparison of immune markers in ichthyosis subtypes, AD, psoriasis and controls using RT-PCR (A-W). mRNA log₂ values were adjusted to hARP expression levels. Stars without bars denote comparison to controls. Stars above bars denote p-values with comparators defined by the bar. LSmean (log₂ expression/hARP) ± SEM. +p<0.1, *p<0.05, **p<0.01, ***p<0.001.

Figure 4.

Unsupervised hierarchical clustering of mRNA expression in AD, psoriasis, ichthyosis, and controls (A) as a heatmap with fold changes/FCHs between diseases and healthy skin. Green box: Cluster of upregulated IL-17-related genes in ichthyosis and psoriasis. +p<0.1, *p<0.05, **p<0.01. red, up-regulation; blue, down-regulation. (B) Unsupervised clustering of samples (phylogenetic tree) based on expression profiles of 45 immune/barrier markers; Distance: Pearson correlation, agglomeration: average.

Figure 5.

Pearson correlation plots of the mRNA gene expression that correlated highest with (A) overall clinical severity score (IASI), (B) erythema severity subscore (IASI-E), and (C) TEWL in ichthyosis subtypes. r = Pearson correlation-coefficient with associated p value (p). y = equation for linear regression (blue line) with its confidence interval (smoothed confidence interval in grey).

Figure 6.

Correlation matrix of all ichthyosis measurements. (A) Unsupervised hierarchical clustering of clinical (blue), with barrier/immune markers (black), including IL-17-synergistic/additive genes (green). Distance: Pearson correlation, algorithm: Mcquitty agglomeration. (B) Correlation heatmap. Pink box: correlations with IASI score. Brown box: the most significant cluster of IL-17- synergistic/additive genes, with green box highlighting the IASI-E sub-cluster. Grey box: pruritus correlations. red, positive correlations; blue, negative correlations. *p<0.05, **p<0.01, ***p<0.001.