Background: Molecular studies in atopic dermatitis (AD) are largely restricted to patients with moderate-to-severe disease.
Objective: To evaluate skin and blood abnormalities in mild, moderate, and severe AD.
Methods: Skin and blood samples were obtained from 61 AD patients (20 mild/limited, 17 moderate, 24 severe) and 20 healthy subjects. Immune and barrier markers were measured in lesional, non-lesional, and healthy skin by qRT-PCR and immunohistochemistry, and in blood using the OLINK proteomic assay.
<strong class="sub-title"> Results: </strong> Cellular markers of epidermal hyperplasia and T-cell/dendritic cell infiltration were increased in AD tissues of all severity patient groups versus controls, while downstream T<sub>H</sub>2, T<sub>H</sub>22, T<sub>H</sub>1, T<sub>H</sub>17-related mediators demonstrated incremental elevations with increasing disease severity, in both lesional and non-lesional skin. While T<sub>H</sub>2 (IL13, CCL17, <em>CCL26</em>) and T<sub>H</sub>22 (IL-22) cytokines were significantly elevated in both AD lesional and non-lesional skin of all patients regardless of severity, mild/limited AD patients showed increases in T<sub>H</sub>1 (IFNG, CXCL9, CXCL10) and T<sub>H</sub>17 (IL-17A, CCL20, CXCL1) markers in lesional, but not non-lesional skin. Treg-related mediators (IL-10, FOXP3) were comparably up-regulated in all groups, without displaying the severity-based gradient in other immune axes. Unsupervised clustering aligned samples along a severity spectrum, where non-lesional mild/limited AD skin clustered with healthy controls. Furthermore, while the blood profiles of moderate and severe AD patients showed gradual increases in T<sub>H</sub>1/T<sub>H</sub>2/T<sub>H</sub>17-related and atherosclerosis/cardiovascular risk (CCL7, FGF21, IGFBP1) proteins, mild/limited AD lacked significant differences versus controls.
<strong class="sub-title"> Conclusion: </strong> Mild/limited AD shows high T<sub>H</sub>2/T<sub>H</sub>22 activation primarily localized to skin lesions, and lacks the systemic inflammation of moderate and severe disease.
Keywords: Atopic dermatitis; OLINK; cytokines; immune tolerance; limited; mild; proteomics; qRT-PCR; severity; systemic inflammation.