Beschreibung:
<jats:title>Summary</jats:title><jats:p>Immune dysfunction, which leads to the suppression of haemopoiesis by cytokines that are secreted by activated T lymphocytes, is considered to play a key role in the pathogenesis of acquired aplastic anaemia (AAA).</jats:p><jats:p>We investigated the intracytoplasmic expression of type‐1 [interferon <jats:italic>γ</jats:italic> (IFN‐<jats:italic>γ</jats:italic>), interleukin (IL)‐2] and type‐2 (IL‐4, IL‐10) cytokines in CD4+ and CD8+ T cells before and after <jats:italic>in vitro</jats:italic> activation in 16 patients with AAA and 17 normal controls. Untreated or refractory patients had a significantly higher proportion of unstimulated CD4+ and CD8+ T cells that produced IFN‐<jats:italic>γ</jats:italic> and IL‐2 whereas the IL‐4 and IL‐10 producing T cells did not differ from that of controls, resulting in a shift of IFN‐<jats:italic>γ</jats:italic>/IL‐4 ratio towards a type‐1 response. Patients in remission had also increased proportion of IFN‐<jats:italic>γ</jats:italic>‐producing unstimulated CD4+ and CD8+ cells, with a parallel rise of IL‐4‐ and IL‐10‐producing cells and normal IFN‐<jats:italic>γ</jats:italic>/IL‐4 ratio. These data indicate that, in newly diagnosed and refractory patients with AAA, CD4+ cells are polarized towards a type‐1 response that in turn leads to activation of cytotoxic CD8+ cells and finally to haemopoietic stem cell destruction. The type‐1 response persists in patients in remission although this effect is compensated by the increase of IL‐4 and IL‐10 production.</jats:p>