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At unstimulated baseline, the frequencies of IL-10-producing CD4+ and CD8+ T cells were significantly higher in atopic asthmatics than in healthy controls. A similar difference was noted in CD4+ T cells between atopic nonasthmatics and healthy controls. T cells circulate systemically from the affected organs to the blood stream via the lymphatic system . Our findings in the peripheral blood may reflect the increased numbers of IL-10-producing T cells in the airways of atopic asthmatics. This speculation is supported by a report showing that IL-10 mRNA-positive T cells are increased in the airways of atopic asthmatics compared with those of healthy controls . Persistence of airway inflammation is frequently observed in biopsy specimens of asthmatics, even when they are symptom free . Based on the concept that a major role of T cell-derived IL-10 may be antiinflammatory, the increase in IL-10-producing T cells may be explained as chronic activation of feedback inhibitory mechanisms . Alternatively, the increase in T cell-derived IL-10 may contribute to the persistence of inflammation through its proallergic ability as an inducer of Igs - in particular, IgE from B cells . Indeed, IL-10 is regarded as one of the pathogenic cytokines in some autoimmune diseases, in which the overproduction of autoimmune antibodies plays a role . Another interesting finding is the increased frequency of IL-10-producing CD8+ T cells in asthmatics, which was not observed in atopic nonasthmatics. While the contribution of activated/memory CD4+ T cells in asthma is widely appreciated, recent investigations have suggested that CD8+ T cells may also be involved in the development of this disease. CD8+ T cells, skewed toward cytotoxic phenotype, similar to Th2-phenotype in CD4+ T cells, acquired a capability for IL-5 production and contributed to virus-induced eosinophilia in mice . In asthmatics, increased numbers of IL-4 or IL-5 mRNA-expressing CD8+ T cells have been shown in airway biopsies, as well as an increased level of IL-4 protein in peripheral blood CD8+ T cells .