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Experimental infection of murine splenic lymphocytes and granulocytes with Toxoplasma gondii RH tachyzoites
J Y Chai,*1J Kook,1S M Guk,1Y P Chang,2 and C K Yun3
Department of Parasitology and Institute of Endemic Diseases, Seoul National University College of Medicine, Seoul 110-799, Korea.
Received April 13, 1997; Accepted May 29, 1997.
Abstract
Toxoplasma gondii, an intracellular protozoan infecting many kinds of eukaryotic cells, has been used to experimentally infect macrophages, epithelial cells, fibroblasts, and various cancer cells, but rarely T and B lymphocytes or granulocytes. The present study was performed to determine the susceptibility of murine (BALB/c or CBA) splenic T and B lymphocytes, and granulocytes to infection with T. gondii RH tachyzoites. The ultrastructure of the infected host cells was observed by TEM, and the degree of intracellular parasite proliferation was quantified using 3H-uracil uptake assay. At 24 hrs post-culture, the host cell cytoplasm was found to contain 1 or 2, or a maximum of 7-8 tachyzoites. Infected T lymphocytes demonstrated a peripherally displaced nucleus, a parasitophorous vacuole enveloping the parasite, and an increased number of mitochondria. In B lymphocytes infected with tachyzoites, RER was not well developed compared to uninfected B lymphocytes. Uninfected granulocytes contained many electron-dense granules, but T. gondii-infected granulocytes demonstrated a decreased number of granules. Based on the 3H-uracil uptake assay, the susceptibility of T and B lymphocytes, and granulocytes, to infection with T. gondii tachyzoites was fairly high irrespective of cell type and strain of mouse. This strongly suggests deterioration in the functioning of infected host immune cells.
Figures
Figs. 1-4 Fig. 1. A thin section of splenic T lymphocytes (arrows) of BALB/c mice experimentally infected in vitro with RH tachyzoites of Toxoplasma gondii, 24 hrs after infection (×1,000). Fig. 2. Ibid, neutrophils (arrows) isolated from the spleen of BALB/c mice and infected in vitro with tachyzoites of T. gondii. Neutrophils contain a few to many tachzoites which presumably divided intracellularly, 24 hrs after infection (×1,000). Fig. 3. Electron micrograph of a T lymphocyte isolated from the spleen of a BALB/c mouse and experimentally infected with tachyzoites of T. gondiiin vitro, 24hrs after infection, characteristically showing the host cell nucleus (N) displaced to the periphery resulting from the parasitophorous vacuole (Pv). The intracellular organelles of the parasite, namely the nucleus (TN), rhoptry (R), and electron-dense body (DB) are observed (white scale: 1 µm). Fig. 4. Electron micrograph of a T lymphocyte isolated from the spleen of a CBA mouse and experimentally infected with T. gondiiin vitro, 24 hrs after infection, showing a tachyzoite (T) surrounded by the parasitophorous vacuole, the slightly displaced host cell nucleus (N) and an increased number of mitochondria (Mt) (white scale: 1 µm).
Figs. 5-8 Fig. 5. Electron micrograph of a B lymphocyte isolated from the spleen of a CBA mouse, 24 hrs after infection with tachyzoites of T. gondii. Illustrated are the nucleus (N), rough endoplasmic reticulum (RER), and T. gondii tachyzoites (T) enveloped by the parasitophorous vacuole (white scale: 1 µm). Fig. 6. Electron micrograph of a B lymphocyte isolated from the spleen of a CBA mouse, 24 hrs after infection with tachyzoites of T. gondii, showing the host cell nucleus (N) and several divided tachyzoites (T) (white scale: 1 µm). Fig. 7. Electron micrograph of a neutrophil isolated from the spleen of a BALB/c mouse, 24 hrs after infection with tachyzoites of T. gondii, showing the host cell nucleus (N) and cytoplasmic granules (G). Many of the tachyzoites (T) divided and occupy almost all the intracellular space of the cell (white scale: 1 µm). Fig. 8. Electron micrograph of a neutrophil isolated from the spleen of a CBA mouse, 24 hrs after infection with tachyzoites of T. gondii, showing the nucleus (N) and granules (G). Within the cytoplasm, 7-8 tachyzoites of T. gondii are seen, and two (arrow heads) are in their endodyogenic phase. The nucleus (TN), conoid (C), rhoptry (R), and electron-dense body (DB) of this parasite are seen (white scale: 0.5 µm).
Tables
Table 1 3H-uracil uptake by RH tachyzoites of T. gondii in murine splenic T and B lymphocytes, and granulocytes
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