In atopic dermatitis (AD), eosinophils likely contribute to disease pathogenesis. In chronic lesions, mature eosinophils are rarely seen histologically, however their granule products are detectable. Increased numbers of eosinophils in the dermis of AD skin lesions may arise from in situ differentiation of eosinophil lineage-committed progenitors (EoP), possibly driven by growth factors such as IL-5. This study quantified mature eosinophils and EoP in skin lesions and the late cutaneous response (LCR) after intradermal allergen challenge and lesions of patients with AD.
Patients with moderate-to-severe AD washed out from systemic steroid for 8 days and were intradermally challenged with allergen and saline control. Biopsies were obtained 24h later from 1) LCR site of intradermal challenges; 2) chronic skin lesion; and 3) unaffected skin, and stained with hematoxylin and eosin (H&E) for eosinophils, and anti-CD34-FITC, anti-IL-5Ra-Cy5, and anti-Von Willebrand factor-TRITC for EoP detection by immunofluorescence. Cells were counted in the papillary dermis and paired t-tests were performed.
EoP and mature eosinophils in skin biopsies of the LCR had perivascular organization. There was a significant increase in EoP and mature eosinophils 24 hour post-allergen compared to post-saline in the LCR (p<0.05). There was a significant increase in EoP in the lesion compared to unaffected skin (p<0.05), but no difference in mature eosinophils stained with H&E.
EoP in situ differentiation may participate in the early development of tissue eosinophilia in patients with AD, which may result in the increased numbers of eosinophils in chronic AD skin lesions.