Background: In this review, present knowledge of atopic eczema immunopathogenesis is summarized, emphasizing recent new findings. Systemic abnormalities in cell-mediated immunity have not been demonstrated firmly in patients with atopic eczema. Within the skin itself, there is evidence for decreased cell-mediated immunity, which is partially correlated with the severity of skin disease. Atopic eczema, however, cannot be regarded as a direct result of decreased cutaneous cell-mediated immunity, since immunophenotyping studies have revealed activated T cells as well as dendritic cells within involved skin. In addition, disease marker studies in peripheral blood indicate vigorous T-cell activation in atopic dermatitis.
Observations: The original observation of IgE molecules on the membranes of Langerhans cells may indicate trapping of IgE allergen complexes, their processing, and subsequent presentation to allergen-specific T cells within involved skin. Recent findings as to the abnormal regulation of IgE synthesis in atopy point to a preferential expansion of interleukin 4 and interleukin 5 producing allergen-specific T cells, leading to increased production of interleukin 4 and thus increased levels of allergen-specific IgE. We have prepared atopic skin as well as peripheral blood-derived T-cell clones and determined their specificity and cytokine production profile. Results indicate in situ production of interleukin 4 and interleukin 5 within involved skin in response to environmental antigens.
Conclusions: These new findings as to the basis of IgE dysregulation in atopy, as well as to the identification of an abnormal cytokine secretion pattern by T cells presumed to be central in immunopathogenesis of atopy-related disorders, suggest a distorted and cytokine-mediated self-perpetuating response of the skin immune system to environmental allergen(s) in the pathogenesis of skin disease in atopy. These observations may have important implications for the development of new therapies for atopic eczema.