الفهرس 
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Abstract
Summary & conclusions
cquired aplastic anemia is a clinical syndrome in which there is a deficiency of red cells, neutrophils, monocytes, and platelets in the blood, and fatty replacement of the marrow with a near absence of hematopoietic precursor cells.
Reticulocytopenia is a constant feature. Neutropenia, monoc-ytopenia, and thrombocytopenia, when severe, are life-threatening because of the risk of infection and bleeding, complicated by severe anemia.
Most cases occur without an evident precipitating cause and are caused by autoreactive cytotoxic T lymphocytes that suppress or destroy primitive CD34+ multipotential hematopoietic cells. The disorder also can occur after
1. Prolonged high-dose exposure to certain toxic chemicals (e.g., benzene, Organochlorine and organophosphate).
2. After specific viral infections (e.g., Epstein-Barr virus, varicella zoster virus and hepatitis virus).
3. As an idiosyncratic response to certain pharmaceuticals (e.g., ticlopidine, chloramphenicol and an antimicrobial agents).
4. As a feature of a connective tissue or autoimmune disorder (e.g., lupus erythematosus, rheumatoid arthritis and Graves’ disease).
5. Rarely, in association with pregnancy.
The final common pathway may be through cytotoxic T-cell autoreactivity, whether idiopathic or associated with an inciting agent since they all respond in a similar fashion to immunosuppressive therapy.