الفهرس 
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Abstract
Eosinophils are type of white blood cells. They comprise approximately 1-6% of the blood’s cellular make-up., characterized by their bright granular red-pink color and double nucleus when stained and viewed under the microscope.
Eosinophils are generally considered to be peripheral blood leukocytes that have an important pro-inflammatory role in various immune disorders.
Eosinophils normally settle in the lamina propria of the gastrointestinal tract. Usually, eosinophils are absent from the esophagus and very few in stomach, scattered variably in small number along small intestine, mostly present in the colon and the appendix, decreasing from cecum to the rectum, to be no more than five eosinophils/high-power field (HPF) in the rectum.
Gastrointestinal eosinophilia is a broad term for abnormal eosinophil accumulation in the gastrointestinal tract, involves many different diseases. These diseases include primary eosinophil associated gastrointestinal diseases, gastrointestinal eosinophilia in hypereosinophilic syndrome, and all gastrointestinal eosinophilic states associated with known causes.
Food allergy is an adverse immune response to food protein. Any food can cause allergy, however, the most common foods that produce allergy in infant and children are cow’s milk, hen’s egg, soybeans, wheat, peanut, tree nuts, fish and shellfish. In GI food allergies, the underlying immune responses may be IgE-mediated, cell-mediated or both. Unlike the acute manifestations seen in IgE-mediated food hypersensitivity, cell-mediated reactions have relatively subacute or chronic symptoms that are difficult to discriminate from gastroenteritis Delayed diagnosis may result in significant growth retardation, anemia and severe malnutrition in the worst cases.
Primary eosinophilic gastrointestinal disorders are defined as disorders that selectively affect the gastrointestinal tract with eosinophil-rich inflammation in the absence of known causes for eosinophilia (e.g. drug reactions, parasitic infections, and malignancy). These disorders include eosinophilic esophagitis, eosinophilic gastritis, eosinophilic gastroenteritis, eosinophilic enteritis, and eosinophilic colitis and are occurring with increasing frequency.
Eosinophilia induced by helminthic infection is mainly dependent on IL-5 generated by TH2 lymphocytes. Eosinophils act against parasites by discharging their cytotoxic granule proteins onto the surface of these multicellular organisms.
Ulcerative colitis is a severe ulcerating inflammatory disease that is limited to the colon and rectum and extends only into the mucosa and submucosa. In contrast, Crohn’s disease, which has also been referred to as regional enteritis (because of frequent ileal involvement) may involve any area of the GI tract and is typically transmural.
Celiac disease is also known as celiac sprue or gluten-sensitive enteropathy. It is an immune-mediated enteropathy triggered by the ingestion of gluten-containing cereals, such as wheat, rye, or barley, in genetically predisposed individuals.
Lymphocytic colitis includes surface epithelial damage with cellular loss and epithelial detachment, infiltration of the surface epithelium with eosinophils and neutrophils, and minimal crypt distortion or active cryptitis. Collagenous colitis shares the histologic features of LC but additionally demonstrates a thickened subepithelial collagen layer.
Connective-tissue disease-especially scleroderma-has been associated with a mast-cell-rich eosinophilic infiltrate in the lamina propria, adjacent to the muscularis mucosae. Mild to moderate eosinophilia is relatively common in cancer tissues, and is sometimes attributed to factors such as radiation therapy, an allergic reaction to tissue necrosis.
Graft-versus-host disease (GVHD) occurs when immunologically competent donor lymphoid cells (which bear different histocompatibility antigens) from the host are placed into an immunosuppressed recipient, usually in the setting of a bone-marrow transplant.
Patients with autoimmune colitis either show a mild lymphocytic infiltration of the epithelium or the epithelium contains large numbers of degranulating eosinophils and mast cells superimposed on a background of mucosal atrophy.
The Hypereosinophilic syndrome (HES) is a rare, multisystem disorder defined by (1) persistent peripheral blood eosinophilia with more than 1500 cells/mm3 for longer than 6 months, (2) no known cause of eosinophilia and (3) signs and symptoms of organ involvement