Toxoplasma gondii: appearance of specific markers during the development of tissue cysts in vitro

Abstract

Cultures were initiated in Madin-Darby bovine kidney (MDBK) cells from ME49 strain bradyzoites. Specific antibody staining showed that two populations of parasites exist, one being a predominant population of tachyzoites that were positive for the tachyzoite-specific marker SAG1 and negative for the bradyzoite-specific marker P36. All of these parasites expressed the dense granule molecule GRA5, which in larger clusters was seen faintly in the membrane of the parasitophorous vacuole. No rosette formation or monolayer destruction was observed. Also seen was a sub-population of bradyzoites that were positive for P36 and negative for SAG1. Approximately 90% of these parasites expressed the matrix molecule P29. These parasites were also positive for the dense granule molecule GRA5, which was highly concentrated in the wall of the cyst. These bradyzoite clusters contained fewer parasites and were smaller in diameter than those expressing tachyzoite markers.

The role of stage-specific oligonucleotide primers in providing effective laboratory support for the molecular diagnosis of reactivated Toxoplasma gondii encephalitis in patients with AIDS

“…In contrast, SAG1 gene-specific primers detected more relapse cases (45.4%) than first episodes (28.7%), although the difference was not significant. In agreement with invitro and in-vivo studies, these findings might suggest that relapsing TE is associated with an increased amount of tachyzoite SAG1 DNA in the CNS associated with rapid parasite replication [15,35,36].…”

“…Positive results were found in 72% of patients with TE relapse and in 25% of those with first episode of TE. Among the 11 patients with TE relapses, seven (nos 2, 3, 5, 7, 11, 15 and 17) had T. gondii DNA in their CSF detectable by these primers, in contrast to four (nos 3,11,14,15) detected by B1-PCR. No relapse cases that were B1-positive were also The detection of larger amounts of bradyzoite-specific genes in patients with TE relapses than in patients with first episodes of TE may be explained in part by the fact that most patients with relapses were treated repeatedly, after the first episode, with chemotherapeutic agents such as pyrimethamine and sulphadiazine, which have been reported to induce bradyzoite antigen expression and enhance cyst production and bradyzoite development [3,42].…”

“…This may account for the failure of PCR which targets the B1 gene [6][7][8][9][10][11]. Recently, cloning of stage-specifically expressed genes, such as SAG1, located in the tachyzoites, or BAG1, SAG4 and MAG1, located in the bradyzoites, has enabled further analysis of regulatory mechanisms that are involved in the stage interconversion and provided insights into the pathogenesis of toxoplasmosis [3,[12][13][14][15][16][17][18].…”

Initial Characterization of CST1, a Toxoplasma gondii Cyst Wall Glycoprotein

“…The tissue cyst is entirely within a host cell, and the limiting membrane of this host cell can be seen by electron microscopy. The tissue cyst wall is a modification of the limiting membrane of the parasitophorous vacuole and is elastic, argyrophilic, and periodic acid-Schiff reactive (12,24). The cyst wall and matrix probably protect bradyzoites from harsh environmental conditions and also provide a physical barrier to host immune defenses.…”

Adjuvanted multi-epitope vaccines protect HLA-A*11:01 transgenic mice against Toxoplasma gondii

“…GRA6 is expressed and secreted by both the tachyzoite and the bradyzoite stages of the parasite. GRA5, another dense granule protein, is present in bradyzoites and is strongly concentrated in the cyst wall (10).…”