Chronic Idiopathic Thrombocytopenic Purpura, Clinical And Basic Research

Immune thrombocytopenic purpura (ITP) is an autoimmune disorder characterized by a low platelet count and mucocutaneous bleeding. The estimated incidence is 100 cases per 1 million persons per year, and about half of these cases occur in children. ITP is classified as primary or as secondary to an underlying disorder and as acute (of six months or less in duration) or chronic ITP. Also, it can be classified as children-onset, adult-onset, or pregnant-onset ITP. Adult-onset and childhood-onset immune thrombocytopenic purpura are strikingly different. Affected children are young (peak age, approximately five years) and previously healthy, and they typically present with the sudden onset of petechiae or purpura a few days or weeks after an infectious illness. Boys and girls are equally affected. In more than 70 percent of children, the illness resolves within six months, irrespective of whether they receive therapy. By contrast, adult ITP is generally chronic, the onset is often insidious, and approximately twice or three times as many women as men are affected.The ITP pathogenesis was studied first by Dr. Harrington in the fifties last century, however, there are still much unknown in it. Because acute ITP in children often follows an infectious event, it suggests that acute ITP may be associated with the immune mechanisms stimulated by the preceding infactions. Acute ITP might be the result of tolerance breakdown because of the antigenic mimicry. Antigenic mimicry is perhaps one of the oldest and most prevalent theories of the tolerance breakdown resulting in autoimmunity. It is caused by molecular structures on infectious or enviroment agents that have similarities to host antigenic structures and stimulate an immune response that then cross-reacts with host antigens (e.g. anti-virus antibodies). Compared with acute ITP, chronic ITP involved in more complex pathogenesis: ① HLA class II moleculars at the cell surface can change the immunogenity of platelets and provoke autoreactive T helper cells. ② The susceptibility involved in FcγR polymorphisms. ③ HLAassociations and genetics in chronic ITP. ④ cytokine profiles and T helper cells polarizations. ⑤ Auto-reactive T cell in chronic ITP. ⑥ Others. e.g. Hp infections or abnormal apoptosis of megakaryocytes. Steroids and...