Toxoplasmosis: The effect of citrate, calcium and magnesium ions on the non-specific antitoxoplasma activity in human sera

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Abstract
Extract The cytoplasm-modifying-antibody (dye) test introduced by Sabin and Feldman ( 1948 Sabin, A. B. and Feldman, H. A. 1948. Science, 108: 660–660. [Crossref], [PubMed], [Web of Science ®] [Google Scholar] ) has been widely used as a diagnostic test for toxoplasmosis. At this laboratory, difficulty has been experienced in obtaining human sera suitable for use as accessory factor owing to the prevalence of a non-specific antitoxoplasma factor that causes about 50 to 70% of organisms to lose their affinity for methylene blue after incubation with undiluted serum. However, one particular blood sample that gave satisfactory results on the day of collection (less than 10% unstained), became unsuitable for use (more than 50% unstained) after overnight storage at 4°C to allow clot retraction before separation of the serum. Even when the serum was separated immediately and frozen overnight, a similar change was observed. The possibility that alterations in dye-test reactivity might be associated with the clotting process led to the observations on dye-test reactivity recorded here. In particular, it has been shown that some human sera with intrinsic antitoxoplasma activity can be rendered satisfactory for use in the dye test by the addition of sodium citrate, although the mechanism of action has not been resolved.

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