مطالعه اولترا ميكروسكوپي توكسوپلاسما گونديي و مكانيسم عمل داي تست در تشخيص توكسوپلاسموزيس

Ultramicroscopic study of Toxoplasma gondii and mechanism of dye test in the diagnosis of toxoplasmosis

Toxoplasma gondii is an obligate intracellular protozoan parasite, capable of infecting all mammals, including human. Although toxoplasmosis is clinically asymptomatic in healthy individuals it can cause severe complication in pregnant women and immuno compromised patients. In this investigation, the ultra structure of RH strain of Toxoplasma gondii and the effects of humoral immunity against the organism on the basis of Sabin-Feldman dye test have been studied using electron microscopy. It was observed that in the sera without specific antibody against Toxoplasma parasites, the cytoplasm of Toxoplasma was stained deeply, specially in the region of ribosornes. In this region, the rough endoplasmic reticulum was seen as dark lines. In those samples the morphology of the Toxoplasma had been altered and was seen swollen. Also it was.found that when Toxoplasma exposed to antibody in the presence gfaccessory factor, its cytoplasm was completely unstained, compared to the deep blue staining of the cytoplasm of Toxoplasma in the mixtures with normal serum. In this mixtures the pellicle of Toxoplasma had been degenerated and there was an apparent extrusion of cytoplasmic contents. In fact, the accessory factor which acts in concert with antibody in human serum, is identical to classical complement pathway and so degenerates the pellicle of Toxoplasma. In addition, the ribosomes which normally present throughout the cytoplasm, lost their ability Jr ostaining in consequence of antibody effects, and thus treated organism failed to take up dye in the test. In these samples the nucleus was stained deeply. Considering the observations obtained in this study, it can be concluded that humoral immunity can kill toxoplasma, but despite the ability of antibody to effectively kill extracelluIar Toxoplasma in vitro, the intracellular habitat of this protozoan in vivo is likely to protect it. from the effects of circulating antibody.