Idiopathic thrombocytopenic purpura pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
AITP is characterized by the production of autoreactive antibodies against one's own platelets, resulting in increased platelet destruction by RES phagocytes
Pathophysiology
Pathogenesis
Acute ITP: Mainly affects children and usually follows a viral or bacterial infection
- Antigenic mimicry - Similar molecular structures on both host cells and infectious agents, inducing a self immune response which cross reacts with the host antigens.
- In acute ITP - anti-viral or anti-bacterial antibodies cross reacts against the patient's platelets.
- Mostly acute ITP is self resolving as infectious agents and antibodies are cleared from the body, causing the loss of anti-platelet reactivity.
- T cells are not involved in the parthenogenesis of acute ITP
Chronic AITP: (platelet counts < 150,000 x 109 per liter x 6 months) usually in adults
- Autoantibody‐induced platelet destruction:
- immune-targeted tissue abnormally expresses selfantigens that are then recognized by autoreactive Th cells.
- true organ-specific autoimmune disorder
- no previous history of an infectious event and almost always requires some form of immunosuppressive therapy
- anti- 72 COOPAMAH ET AL body specificities are directed against several platelet glycoprotein epitopes
- associated with T-cellrelated and cytokine abnormalities
- Autoantibody‐induced platelet destruction:
- Abnormal IgG auto-antibody recognizes glycoprotein IIb/IIIa, glycoprotein Ib/IX complex, GP Ia/IIa, and GP VI etc
- majority of these autoantibodies are IgG, but IgM and IgA can also be identified in some patients with AITP
- Predominantly IgG auto-antibodies constitute the majority of antibodies but IgM and IgA antibodies can also be found in some of ITP patients.
- Auto-antibodis binds to the circulating platelet membranes through glycoproteins
- Autoantibody-coated platelets induce Fcg receptors and bind to antigen-presenting cells (Splenic macrophages or dendritic cells) in the reticuloendothelial system
- The autoantibody-coated platelets undergo phagocytosis by splenic macrophages and peripheral blood neutrophils.
- Autoreactive T lymphocyte‐mediated platelet lysis
- Abnormal Th call defect leads to differentiation of direct autoreactive B cells further leading to secretion of IgG auto-antibodies.
- T cells act directly on the megakaryocytes in the bone marrow
- Antibody production in ITP appears to be driven by CD4-positive helper T cells reacting to platelet surface glycoproteins, possibly involving CD40:CD40L co-stimulation . Splenic macrophages appear to be the major antigen-presenting cells
- Autoantibody‐induced platelet destruction:
- Immune‐mediated decreased platelet production:
- abnormal thrombopoiesis
- degenerative changes in both nuclei and cytoplasm
- reduced platelet turnover
- megakaryocyte damage
- autoantibody‐induced suppression of in vitro megakaryocytopoiesis
-
Genetics
Associated Conditions
Conditions associated with
Gross Pathology
On gross pathology, characteristic findings of itp include:
- Acute
- Chronic
Microscopic Pathology
On microscopic histopathological analysis, characteristic findings of itp include:
- Acute
- Chronic
References