The possible roles of CD8+ cells in the abnormal T cell-dependent B-cell activation in Graves' disease were investigated by analysing lymphocyte subsets in peripheral blood mononuclear cells (PBMC) and their production of soluble factors and cytokines such as IL-10 in patients with Graves' disease, Hashimoto's thyroiditis and normal controls. The PBMC were separated into CD8+ and CD8-depleted cells by magnetic separation columns, and cultured for 7 days with or without anti-CD40 monoclonal antibodies and IL-4. The culture supernatant was assayed for sCD23 and IL-10 using EIA, and the remaining cells were analysed by flow cytometry. Stimulation with anti-CD40 antibody together with IL-4 increased sCD23 levels and the number of CD23+ cells. The latter was further augmented by depletion of CD8+ cells. This combination of B cell stimulants increased production of IL-10 by PBMC from patients with Graves' disease. The CD40- and IL-4-activated production of IL-10 was decreased by CD8+ cell depletion. In contrast, constitutive production of IL-10 was increased after CD8+ cell depletion in a group of patients with low basal secretion levels (<35 ng/ml). It was, however, decreased in a group with higher basal production levels, but such a relationship was not found in the normal control group. Thus, T cell-dependent B-cell activation via a CD40 pathway activates CD23+ cells, leading to over-production of IL-10 and a shift of the Th1/Th2 balance to Th2 dominance, while CD8+ cells may suppress this activation to counteract the Th2 deviation in Graves' disease.
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