الفهرس 
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Abstract
Several species of intestinal protozoa have been identified in human stool samples. G.lamblia is the most frequently encountered protozoan pathogen. It has a broad clinical spectrum ranging from asymptomatic infection or mild self limiting gastrointestinal upset to prolonged illness with malabsorption. This variation is attributed to differential host susceptibility or parasite strain differences G.lamblia causes morphological and functional abnormalities of the small intestinal mucosa resulting in diarrhea and malabsorption. These pathological changes are exacerbated by host inflammatory and immune responses. Amoebiasis is also a common parasite infection. It is well established that parasites previously known as E.histolytica consist of actually of two morphologically identical species; the pathogenic species or E.histolytica and the non pathogenic E.dispar. E.histolytica is responsible for all cases one of invasive amoebiasis and sometimes causes asymptomatic infection E. dispar, which is much more common, has never been documented to cause colitis or liver abscess. The two species can be differentiated by isoenzyme analysis of cultured isolates, typing by monoclonal antibodies to certain antigens and distinctive genomic DNA. Cytokines consist a group of protein that regulate many immune and inflammatory responses. Thelper lymphocytes are separated into T helper-1 cytokine secretion pattern. The cytokines (TFN-?, interleukin-2 and tumor necrosis factor) promote cellular immune responses. Th 2 cytokines (IL4, IL5, IL6 and IL10) regulate immune responses. The type of Thelper cell that predominates in a parasitic infection influence the course of the disease. The identification of protective T lymphocytes subset and he relevant T cell epitope are important for the development of effective vaccines against parasitic diseases. In giardiasis, IFN-? activates macrophage phagocytic activity. Macrophages destroy the ingested trophozoites and act as antigen presenting cells causing sensation of the lymphocytes and enhancement of the immune response. In amoebiasis IFN-? activates the amoebicidal activity of macrophages and neutrophils and enhance their capacity to resist the cytolic effect of E.histolytica trophozoites. In addition, IFN-? suppress protein and DNA synthesis by the parasite. The present study was performed to detect intestinal protozoa among school students, to differentiate between E.histolytica and E.dispar infections and to study serum cytokine profile in symptomatic and asymptomatic students infected with G.lamblia, E.histolytica or E.dispar. The students of the study included 667 school students. They were among these attending 6 health insurance clinics in Alexandria. Some students were subjecting to interviewing questionnaire and clinical examination. Stool samples were collected and examined using merthiolate iodine formaldehyde concentration technique to detect protozoan cysts and helminthes eggs and to assess the intensity of G.lamblia and E.histolytica/ E.dispar infections Modified Ziehl Neeben staining was used to detect intestinal coccidia. A stool ELISA was performed to detect E.histolytica coproantigen in E.histolytica/E.dispar microscopically positive samples. Serum IFN-? (Th 1 marker) and IL4 (Th 2 marker) levels were measured by ELISA in 30 students having G.lamblia infection,23 students having E.dispar and 7 students with E.histolytica infection, twenty students free of parasitic infection were included as control.