John W. Semple

John W. Semple is a Canadain Scientist at St. Michael's Hospital and a Professor of Pharmacology at the University of Toronto. He was born in Windsor, Ontario in 1959 and received his PhD in Immunology at Queen's University at Kingston, Ontario. In 1991, Semple, along with John Freedman, discovered a T helper cell defect in patients with the bleeding disorder called immune thrombocytopenic purpura (ITP). [1] . ITP is the condition of having a low platelet count (thrombocytopenia) and most causes appear to be related to antibodies against platelets. Very low platelet counts can lead to a bleeding diathesis and purpura. The T cell defect was initially shown to be an exaggerated interleukin-2 response when T cells were cultured with platelets in vitro. Subsequently, this cytokine abnormality was shown by others to be responsible for many of the autoimmune mechanisms causing the disorder. [2] [3] [4] [5] [6] The importance of understanding the T cell defects in ITP is that novel therapies aimed at these cells may significantly benefit patients with ITP.

1. Semple JW et al. Increased antiplatelet T helper lymphocyte reactivity in patients with autoimmune thrombocytopenia. Blood 8:2619-2625.

2. Cooper N et al. The pathogenesis of immune thrombocytopaenic purpura. Brit J Haematol 2006;133:364–374.

3. Semple JW et al. Differences in serum cytokine levels in acute and chronic autoimmune thrombocytopenic purpura: relationship to platelet phenotype and antiplatelet T-cell reactivity. Blood 1996:87:4245-4254.

4. Kuwana M et al. Autoreactive T cells to platelet GPIIb-IIIa in immune thrombocytopenic purpura. Role in production of anti-platelet autoantibody. J Clin Invest 1998;102:1393-1402.

5. Olsson B et al. T-cell-mediated cytotoxicity toward platelets in chronic idiopathic thrombocytopenic purpura. Nature Medicine 2003;9:1123–1124.

6. Stasi R et al. Analysis of regulatory T cell changes in patients with idiopathic thrombocytopenic purpura receiving B-cell depleting therapy with rituximab. Blood 2008;112:1147-1150.