Idiopathic Thrombocytopenic Purpura - Pathogenesis

Pathogenesis

In many cases, ITP's cause is not idiopathic but autoimmune, with antibodies against platelets being detected in approximately 60 percent of patients. Most often these antibodies are against platelet membrane glycoproteins IIb-IIIa or Ib-IX, and are of the immunoglobulin G (IgG) type. The famous Harrington–Hollingsworth experiment established the immune pathogenesis of ITP.

The coating of platelets with IgG renders them susceptible to opsonization and phagocytosis by splenic macrophages, as well by Kupffer cells in the liver. The IgG autoantibodies are also thought to damage megakaryocytes, the precursor cells to platelets, but this is thought to contribute only slightly to the decrease in platelet numbers. Recent research now indicates that impaired production of the glycoprotein hormone thrombopoietin, which is the stimulant for platelet production, may be a contributing factor to the reduction in circulating platelets. This observation has led to the development of a class of ITP-targeted drugs referred to as thrombopoietin receptor agonists.

The stimulus for auto-antibody production in ITP is probably abnormal T cell activity. Preliminary findings suggest that these T cells can be influenced by drugs that target B cells, such as rituximab.