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PROLIFERATION OF Toxoplasma gondii AND ITS CYST-FORMATION IN MOUSE BRAINS

English (英語)

The Kobe journal of the medical sciences

26(4)

253-267

1980-12

The present paper describes studies of the proliferation of Toxoplasma gondii (5-273 strain, abbreviated to Tp), especially in relation to the formation, distribution and maturation of the cyst in ICR albino mouse brains by light and electron microscopy. The Tp with which the mouse was infected reached the brain on the 9th day and formed the cyst on the 12th day after inoculation. The cyst size was an average of 15 μm in diameter. On the 15th day the cyst diameter reached 30 μm, and thereafter increased gradually with the increase of the antibody titer of the Tp. Under the transmission electron microscopic observation of the mouse brain on the 12th day after inoculation, the earliest stage of the cyst could be observed. The immature cyst consisted of a homogeneous clot which was electron less-dense, including a few trophozoites. There was a electron lucent space around this structure, which contained mitochondria, a filamentous substance, and other small bodies. However, there was no definite cyst wall around this substance. The outer layer of the cyst recovered from the 1st month after inoculation could be observed as an electron-dense membranous structure, fusing precipitates derived from the host cell in some areas. A structure which could be fully recognized as the cyst wall was found in the brain in the 2nd month after inoculation. This cyst wall had electron-density entirely different from that of the homogeneous substance filling the space between the trophozoites in the cyst and covered the cyst with uniform thickness. In cysts containing polygonal shaped trophozoites, the outer space surrounding the cyst was often extremely narrow or hardly seen. The cyst wall in the 3rd month after inoculation became more conspicuous and electron-dense. It consisted not of homogeneous material, but of a filamentous structure probably derived from the host cell membrane, which was buried in many parts of the cyst wall. Most of the cysts in the 4th month after inoculation resembled those obtained from the 2nd and 3rd months after inoculation. Some of them were similar to the cysts observed on the 12th day after inoculation. From the results obtained so far, it was suggested that the antibody production is related to the process of cyst maturation rather than its formation, and that the cyst wall originated from the secretion of the protozoal cell and host-cellular debris.

ultrastructure

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