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Tissue cyst rupture in mice chronically infected with Toxoplasma gondii. An immunocytochemical and ultrastructural
D J Ferguson1, W M Hutchison, E Pettersen
1Nuffield Department of Pathology, University of Oxford, John Radcliffe Hospital, UK.
Abstract:
The incidence and effect of tissue cyst rupture in the brains of mice chronically infected with Toxoplasma gondii was studied by immunocytochemistry and electron microscopy. Cyst rupture was extremely rare (2 of 750 tissue cysts) irrespective of the interval post-infection. The event was associated with a rapid cell-mediated immune response, giving rise to microglial or inflammatory nodules. Macrophages were observed to engulf and degrade the cystozoites and cyst debris. Initially, the nodules contained large amounts of immunologically reactive material, but this was degraded with the majority (94%) of lesions containing no recognizable parasites or Toxoplasma antigens. There was little evidence of parasite multiplication or new cyst formation associated with cyst rupture. This study shows that although intermittent cyst rupture occurs, in immunocompetent individuals the immune response limits the potential damage from the release of large numbers of infective organisms to small microglial/inflammatory nodules.
Insights
Tissue cyst rupture in Toxoplasma gondii infected mouse brains is rare. In immunocompetent hosts, the immune response effectively contains parasite release, forming small inflammatory nodules.
Area of Science:
- Immunology
- Neuroscience
- Parasitology
Background:
- Toxoplasma gondii is a common protozoan parasite.
- Chronic infection can lead to the formation of tissue cysts in the brain.
- The behavior of these cysts and the host response to their rupture are not fully understood.
Purpose of the Study:
- To investigate the incidence and consequences of Toxoplasma gondii tissue cyst rupture in the mouse brain.
- To characterize the host immune response to cyst rupture events.
Main Methods:
- Immunocytochemistry and electron microscopy were used to examine mouse brain tissue.
- Analysis focused on identifying and characterizing tissue cysts and inflammatory responses.
Main Results:
- Tissue cyst rupture was observed infrequently (0.27% incidence).
- Rupture triggered a rapid cell-mediated immune response, forming microglial nodules.
- Macrophages degraded released parasites and debris, with 94% of lesions showing no recognizable parasite antigens.
- Little evidence of parasite multiplication or new cyst formation was associated with rupture.
Conclusions:
- Intermittent Toxoplasma gondii tissue cyst rupture occurs in the brain.
- The host immune response in immunocompetent individuals effectively controls parasite dissemination following rupture.
- Damage from cyst rupture is limited to small inflammatory nodules, preventing widespread infection.