His research is aimed at understanding the cellular immune mechanisms responsible for the generation of IgG antibodies that recognize platelet antigens. These antibodies can lead to clinically significant adverse effects such as autoimmunity causing immune thrombocytopenia (ITP) and alloimmunity causing platelet transfusion refractoriness. In ITP, for example, his laboratory is interested in how platelet antigens are processed and presented by antigen-presenting cells to activate T lymphocytes. In platelet refractoriness, his group studies the pro-inflammatory nature of platelets responsible for adverse reactions during platelet transfusions, particularly how platelet Toll-like receptor expression modulates innate immune mechanisms. His laboratory also studies the recipient immune mechanisms that cause Transfusion Related Acute Lung Injury (TRALI), a serious complication of transfusion. Professor Semple is the recipient of many awards and a member of several organizations, including the American and European Societies of Hematology and has delivered over 250 presentations at local, national and international meetings. He is currently the Scientific Secretary of the International Society of Blood Transfusion and sits on the editorial board of the journals Blood, Haematologica and Transfusion. He has served as a reviewer for numerous journals and granting agencies. Professor Semple has published more than 200 papers in the area of platelet immunology and transfusion medicine.