Novel 17-kilodalton Leishmania antigen revealed by immunochemical studies of a purified glycoprotein fraction recognized by murine T lymphocytes

Tight junctional inhibition of entry of Toxoplasma gondii into MDCK cells

Various conditions of cultures were performed to investigate the role of tight junctions formed between adjacent MDCK cells on the entry of Toxoplasma. When MDCK cells were cocultured with excess number of Toxoplasma at the seeding density of 1 x 10(5), 3 x 10(5), and 5 x 10(5) cells/ml for 4 days, the number of intracellular parasites decreased rapidly as the host cells reached saturation density, i.e., the formation of tight junctions. When the concentration of calcium in the media (1.8 mM in general) was shifted to 5 microM that resulted in the elimination of tight junction, the penetration of Toxoplasma increased about 2-fold (p less than 0.05) in the saturated culture, while that of non-saturated culture decreased by half. Trypsin-EDTA which was treated to conquer the tight junctions of saturated culture favored the entry of Toxoplasma about 2.5-fold (p less than 0.05) compared to the non-treated, while that of non-saturated culture decreased to about one fifth. It was suggested that the tight junctions of epithelial cells play a role as a barrier for the entry of Toxoplasma and Toxoplasma penetrate into host cells through membrane structure-specific, i.e., certain kind of receptors present on the basolateral rather than apical surface of MDCK cells.

Membrane proteins and their antigenicity of Toxoplasma gondii

Surface membrane proteins of virulent RH strain and tissue cyst-forming Fukaya strain of Toxoplasma gondii were analyzed by SDS-polyacrylamide gel electrophoresis after LPO-catalyzed surface iodination and lectin blotting, then identified the zoite-specific antigens. Prior to the analyses, purification of RH tachyzoites from mouse peritoneal exudate and of Fukaya bradyzoites from mouse brain tissues were performed by centrifugation on the discontinuous Percoll density-gradient. Tachyzoites were obtained at the interface of 50 per cent and 60 per cent Percoll solution and brain cysts were harvested at the interfaces of 40-50 per cent and 50-60 per cent, then bradyzoites were obtained by treating the cysts with hypertonic solution. The LPO-catalyzed iodination detected 15 KDa and 14 KDa proteins of bradyzoites and 30 KDa protein of tachyzoites as major bands with several other minor bands. But Con A blotting revealed some bands of 200 K-50 KDa glycoproteins of bradyzoites and 52 KDa band as major and minor bands of 33 K-20 KDa of tachyzoites. Phytohemagglutinin did not detect any band in the two forms. EITB with anti-Fukaya antibody and anti-RH antibody revealed cross-reactivities between the two forms. Despite the cross-reactivity, anti-Fukaya antibody reacted with 15 KDa band of bradyzoites specifically and, anti-RH antibody with 52 KDa, 30 KDa, and 25 KDa bands of tachyzoites, respectively. It was identified that 15 KDa protein in bradyzoite, which was not a glycoprotein, was a major membrane protein with sufficient antigenicity, and in the case of tachyzoite, 52 KDa surface glycoprotein (gp52) with specific antigenicity might be added to the major surface protein, p30.