['The aim of the study was to determine whether the clinical outcome of double-blind, placebo-controlled food challenges of patients with atopic dermatitis would be associated with changes in lymphocyte functions.', "Peripheral blood mononuclear cells were prepared from 19 children with atopic dermatitis and stimulated in vitro with the suspected allergen (cow's milk, hen's egg), tetanus toxoid, and pokeweed mitogen. After 14 days in culture, quantitative and qualitative distribution of cell surface marker expression was assessed by flow cytometry, and results were compared with the clinical outcome of a subsequent oral food challenge.", 'After stimulation with the allergen, a significant increase of CD4+CD45RO+ T cells (p < 0.05) was detected selectively for patients showing severe clinical reactions. This increase was not detected for patients with mild or no reactions or in six nonatopic control subjects. Increased expression of CD45RO was paralleled by a significant decrease in L-selection expression (p < 0.05) for the same patient group.'] Are severe allergic reactions to foods predicted by increases of CD4+CD45RO+ T cells and loss of L-selectin expression?