Regulation of allergic inflammation by skin-homing T cells in allergic eczema

Background: In allergic inflammations of the skin, the pivotal role of CD45 RO+ (memory/effector) T cells expressing the cutaneous lymphocyte-associate d antigen (CLA) was demonstrated. In both atopic dermatitis (AD) and contac t dermatitis (CD), T cells specific to skin-related allergens were confined to the CLA+ T cell population. Our research was aimed to further character ize these T cells in AD. Methods: CD4+ and CD8+ subsets of CLA+ CD45RO+ T c ells were purified from peripheral blood of AD patients and healthy control individuals. We studied, in vivo activation patterns, cytokine profiles, i mmunoglobulin isotype regulation and the influence of these cells on eosino phil survival and apoptosis. Results: The CLA+ CD45RO+ T cells represent an invivo-activated memory/effector T cell subset as shown by surface express ion of activation markers, spontaneous proliferation and a lower activation threshold via TCR/CD3 triggering. These cells contain and spontaneously re lease high amounts of preformed IL-5 and IL-13 but only very little IL-4 an d IFN-gamma in their cytoplasm, as demonstrated by intracellular cytokine s taining immediately after purification. Moreover, CLA+ memory/effector T ce lls induce IgE production in B cells and enhance eosinophil survival by inh ibiting eosinophil apoptosis in AD. In comparison, the CLA- population repr esents a resting memory T cell fraction, induces rather IgG4 in B cells and does not show any effect on eosinophil survival and apoptosis. Conclusion: Our results indicate that in-vivo-activated both CD4+ and CD8+ memory/effe ctor T cells with skin-homing property play a specific and decisive role in the pathogenesis and exacerbation of AD. In contrast, resting memory T cel ls of atopic individuals retain normal, nonallergic immune functions.