Intrinsic atopic dermatitis shows similar TH2 and higher TH17 immune activation compared with extrinsic atopic dermatitis

Abstract

Background: Atopic dermatitis (AD) is classified as extrinsic and intrinsic, representing approximately 80% and 20% of patients with the disease, respectively. Although sharing a similar clinical phenotype, only extrinsic AD is characterized by high serum IgE levels. Because most patients with AD exhibit high IgE levels, an "allergic"/IgE-mediated disease pathogenesis was hypothesized. However, current models associate AD with T-cell activation, particularly TH2/TH22 polarization, and epidermal barrier defects.

Objective: We sought to define whether both variants share a common pathogenesis.

Methods: We stratified 51 patients with severe AD into extrinsic AD (n = 42) and intrinsic AD (n = 9) groups (with similar mean disease activity/SCORAD scores) and analyzed the molecular and cellular skin pathology of lesional and nonlesional intrinsic AD and extrinsic AD by using gene expression (real-time PCR) and immunohistochemistry.

Results: A significant correlation between IgE levels and SCORAD scores (r = 0.76, P < 10(-5)) was found only in patients with extrinsic AD. Marked infiltrates of T cells and dendritic cells and corresponding epidermal alterations (keratin 16, Mki67, and S100A7/A8/A9) defined lesional skin of patients with both variants. However, higher activation of all inflammatory axes (including TH2) was detected in patients with intrinsic AD, particularly TH17 and TH22 cytokines. Positive correlations between TH17-related molecules and SCORAD scores were only found in patients with intrinsic AD, whereas only patients with extrinsic AD showed positive correlations between SCORAD scores and TH2 cytokine (IL-4 and IL-5) levels and negative correlations with differentiation products (loricrin and periplakin).

Conclusions: Although differences in TH17 and TH22 activation exist between patients with intrinsic AD and those with extrinsic AD, we identified common disease-defining features of T-cell activation, production of polarized cytokines, and keratinocyte responses to immune products. Our data indicate that a TH2 bias is not the sole cause of high IgE levels in patients with extrinsic AD, with important implications for similar therapeutic interventions.

Keywords: AD; Atopic dermatitis; DC; Dendritic cell; FLG; FOXP3; Filaggrin; Forkhead box protein 3; IHC; IgE; Immunohistochemistry; OX40 ligand; OX40L; RT-PCR; Real-time PCR; S100 proteins; TNF ligand superfamily 10; TRAIL; T cell; eczema; extrinsic; human skin; intrinsic; keratinocytes.

Figure 1

Scatter plot of the correlation between IgE and Scoring of atopic dermatitis (SCORAD) in extrinsic (red) and intrinsic (blue) atopic dermatitis (AD) categories; lines represent linear regression within each group. Only extrinsic AD exhibits a significant Pearson correlation between SCORAD and IgE (R=0.76, p=3.7×10⁻⁷), which is lacking in intrinsic AD (R=0.11, p=0.77).

Figure 2

Representative H&Es and immunohistochemistry of lesional and non-lesional skin of extrinsic and intrinsic atopic dermatitis (AD) patients. A; H&E demonstrates similar hyperplasia in extrinsic and intrinsic lesions. B–F; Large T-cell (CD3⁺), myeloid dendritic cell (DC) (CD11c⁺), mature DC (CD83⁺), inflammatory DC (FCεRI⁺), and atopic DC (OX40L⁺) infiltrates are evident in lesional skin of both groups. (10x). ANL, non-lesional; AL, lesional.

Figure 3

Bar-plots of cell-counts (immunohistochemistry) in lesional and non-lesional intrinsic and extrinsic atopic dermatitis (AD). A–B, Similar epidermal hyperplasia (Thickness, Ki67⁺). C–L, Both variants showed significant increases (greatest in intrinsic patients) in T-cells (CD3⁺, CD8⁺), various dendritic cells (DCs), and Langerhans cells (CD11c⁺, CD1a⁺, CD83⁺, CD1c⁺, FcεRI⁺, TRAIL⁺, OX40L⁺) in lesional versus non-lesional skin. M–O, Neutrophils (NE) were increased in intrinsic lesions; extrinsic lesions exhibited increased eosinophils (MBP⁺) and plasmacytoid DCs (BDCA2⁺). Degree of significance between any comparisons indicated if p<0.1. Asterisks in parenthesis (top-right corners) represent significance of the interaction term (Anova model); if present, the AD phenotypes greatly differ between the variants. Mean±SEM. *p<0.10, **p<0.05, ***p<0.01, ****p<0.001. ANL, non-lesional; AL, lesional.

Figure 4

Bar-plots of mRNA expression in lesional and non-lesional skin from intrinsic and extrinsic patients. A-DD, Similar hyperplasia and activation of all inflammatory axes characterize lesional versus non-lesional skin in both variants. Intrinsic lesions exhibited more significant increases in markers of inflammation, Th1, Th22, Th17, and Tregs. Degree of significance between any comparisons indicated if p<0.1. Asterisks in parenthesis (top-right corners) represent significance of the interaction term (Anova model); if present, the AD phenotypes greatly differ between the variants. Mean±SEM. *p<0.10, **p<0.05, ***p<0.01, ****p<0.001. ANL, non-lesional; AL, lesional.

Figure 5

Word-clouds representing the atopic dermatitis (AD) phenotypes, as determined by lesional and non-lesional differences (by IHC, RT-PCR) for (A, D) intrinsic and (B, E) extrinsic AD. Word sizes are proportional to fold-change (FCH) differences, which are scaled relative to the numbers in black. Significance, up/down-regulation indicated by color (see key). Scatter-plots compare extrinsic with intrinsic phenotypes, in C) IHC and F) RT-PCR. Circle diameter represents relative differences; darker colors represent increased significance.

Figure 6

Word-clouds representing correlations between cellular and molecular markers (IHC, RT-PCR) and disease severity (SCORAD) in lesional A) intrinsic and B) extrinsic atopic dermatitis. Words in the clouds are proportional to the correlation coefficient between markers and SCORAD and are color-coded for significance and up/down-regulation (see key). A perfect correlation is indicated by 1 (black).