Background A small subgroup of atopic dermatitis (AD) patients with normal serum IgE levels and without specific IgE sensitization has been termed ‘intrinsic type of AD’ (ADi) as a counterpart to the term ‘extrinsic type of AD’ (ADe). However, there are neither molecular markers nor clinically diagnostic tools for distinguishing between ADi and ADe.
Objective The present studies were undertaken to clarify the pathogenesis and in vivo cytokine micromilieu of ADi patients in comparison with ADe patients.
Methods We used semiquantitative RT-PCR to investigate the expression of various cytokines and assessed the tissue eosinophil counts in skin biopsies from both types of AD patients.
Results Although there was no significant difference of cellular infiltrates in the lesional skin between ADe and ADi patients, ADe had significantly increased tissue eosinophilia than ADi. Based on our RT-PCR, the expression patterns of cytokines could be categorized into four groups. The first group includes IL-5, IL-13, and IL-1β, whose levels of mRNA expression were higher in both types of AD patients than non-atopic (NA) subjects, while ADe patients had even higher levels than ADi patients. The second group includes interferon-gamma (IFN-γ), IL-12, granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-4, and IL-10, whose levels of mRNA expression were elevated in both types of AD patients without differences between ADe and ADi patients. The third group includes tumour necrosis factor-alpha (TNF-α), whose mRNA expression was more decreased in both types of AD patients than NA, and the fourth group includes IL-6 and transforming growth factor-beta (TGF-β), which did not show any differences among the three groups.
Conclusion These current data demonstrate that the expressions of cytokines IL-5, IL-13, and IL-1β mRNA and the number of dermal infiltrating eosinophils are increased in ADe patients compared with ADi patients.