Idiopathic Thrombocytopenia Purpura (ITP) involves antibodies directed toward which combination of cells?

• A. Platelets
• B. Megakaryocytes
• C. Both platelets and megakaryocytes
• D. Fibrinogen

Answer: (C)

The key idea is that ITP involves autoimmune antibodies that can attack both the circulating platelets and the bone marrow precursors that make them, the megakaryocytes. Anti-platelet antibodies (usually IgG) bind platelets and mark them for destruction by splenic macrophages, leading to peripheral thrombocytopenia. At the same time, there is evidence that these antibodies can also target megakaryocytes in the bone marrow, impairing their maturation and platelet production. So you get both increased destruction of platelets and decreased production, which is why the correct choice involves both platelets and megakaryocytes. Fibrinogen is not the target of ITP antibodies, so it isn’t involved here.