Reduced transforming growth factor‐β1 production by mononuclear cells from patients with active chronic idiopathic thrombocytopenic purpura

Summary. Chronic idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder in which activated T‐helper (Th) cells and different Th‐cell cytokines might play an important role. We have recently reported that chronic ITP patients in remission had elevated plasma levels of the Th3 cytokine transforming growth factor‐β1 (TGF‐β1), possibly as a part of a bystander immune suppression. In the present study we found that, in ITP patients with active disease [platelet count (plc) < 50 × 10 9 /l], mitogen‐stimulated peripheral blood mononuclear cells (PBMC) had a significantly reduced production of TGF‐β1 (444 ± 178 pg/ml; n = 6) compared with patients with plc 50–150 × 10 9 /l (1293 ± 374 pg/ml; n = 9; P < 0·05), patients with plc > 150 × 10 9 /l (1894 ± 244 pg/ml; n = 12; P < 0·005) and healthy controls (1698 ± 241 pg/ml; n = 10; P < 0·01). Nineteen per cent of ITP patients expressed a platelet‐induced PBMC proliferation. Surprisingly, 22% of the ITP patients had a PBMC proliferation below the normal range, i.e. a suppressed proliferation in the presence of platelets; five of these six patients had active disease. In summary, this study demonstrated that chronic ITP patients with active disease had reduced PBMC production of the Th3 cytokine TGF‐β1. This result gives further support to the theory that chronic ITP in active phase is associated with a downregulated Th3‐response.