Tissue eosinophilia in acute and chronic atopic dermatitis: a morphometric approach using quantitative image analysis of immunostaining

Background The frequency and amount of tissue eosinophilia in spontaneous lesions of acute and chronic atopic dermatitis (AD) are still a matter of controversy, and little is known about the distribution of eosinophilia in skin. Objectives To give a quantitative description of tissue eosinophilia in spontaneous lesions of acute and chronic AD based on morphometric data. Methods Thirty-one lesional skin biopsies of AD were evaluated using our recently described method for the quantitative assessment of eosinophilic granule protein (EGP) deposition by image analysis of immunostaining using the antibodies EG1, EG2, MBP, EPO and neutrophil elastase (NE). The frequency, amount and distribution of protein deposition including extracellular EGP deposition as an indicator of complete activation and degranulation of eosinophils were determined. Eosinophil count was performed in addition. Histopathological parameters of acute dermatitis (spongiosis) and chronic dermatitis (epidermal hyperplasia) were scored to look for a correlation with tissue eosinophilia. Results Tissue eosinophilia was found in nearly all biopsies (30 of 31). The most protein was detected by EG2, followed by EG1, MBP and EPO, with very small amounts of NE. A superficial tissue distribution of eosinophilia was found, with <10% of total EGP deposition below a depth of 1.39 mm from the epidermis. Eosinophils were involved in acute, spongiotic dermatitis, but more tissue eosinophilia including EGP deposition was detected in lesions with pronounced epidermal hyperplasia than in biopsies without. Conclusions These data provide further evidence for the involvement of activated eosinophils in acute and chronic AD by a new quantitative in situ approach. Pronounced tissue eosinophilia, especially EGP deposition as the result of complete activation of eosinophils, is found in chronic AD and may be involved in the development or maintenance of chronicity.