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Unique differences in infectivity and seroreactivity of Toxoplasma harvested from mice infected for different lengths
R E McCabe1, J R Catterall, J S Remington
1Department of Immunology and Infectious Diseases, Palo Alto Medical Foundation, California 94301.
Abstract:
For use in experiments, Toxoplasma of the RH strain are usually harvested from mouse peritoneal cavities 48 hr (2-day Toxoplasma) or more after intraperitoneal inoculation. In this report we show that Toxoplasma harvested at 24 hr (1-day Toxoplasma) after inoculation are much more infective for and replicate to a greater degree within mouse resident peritoneal macrophages in vitro and are much more resistant to the cidal activity of activated mouse peritoneal macrophages and resident rat peritoneal macrophages than are 2-day Toxoplasma. Ingestion of 1-day Toxoplasma by macrophages did not trigger the respiratory burst as measured by reduction of nitroblue tetrazolium (NBT), but coating 1-day Toxoplasma with specific antibody did result in reduced NBT. However, coating 1-day Toxoplasma with specific antibody did not markedly decrease infectivity for macrophages in vitro, unlike decreased infectivity observed when 2-day Toxoplasma are coated with specific antibody. Use of 1-day Toxoplasma in the dye test resulted in a 5-fold decrease in titer of specific antibody in human sera. Use of Toxoplasma harvested 24 hr after infection may serve as a new tool to probe virulence factors of Toxoplasma and of host cells' antimicrobial mechanisms.
Insights
Newly identified 24-hour Toxoplasma gondii (1-day Toxoplasma) are more infectious and resistant to host defenses than 48-hour parasites. This finding offers new tools for studying Toxoplasma virulence and host immunity.
Area of Science:
- * Immunology
- * Infectious Diseases
- * Parasitology
Background:
- * Toxoplasma gondii is an opportunistic parasite.
- * Standard experimental protocols involve harvesting tachyzoites 48 hours post-infection.
- * The impact of tachyzoite age on infectivity and host immune evasion is not fully understood.
Purpose of the Study:
- * To investigate the infectivity and host immune resistance of 24-hour Toxoplasma (1-day Toxoplasma) compared to 48-hour Toxoplasma (2-day Toxoplasma).
- * To explore the role of tachyzoite surface antibodies in modulating host cell interactions and infectivity.
Main Methods:
- * Comparison of infectivity and replication of 1-day and 2-day Toxoplasma in mouse peritoneal macrophages in vitro.
- * Assessment of tachyzoite resistance to the cidal activity of activated mouse and rat peritoneal macrophages.
- * Measurement of macrophage respiratory burst using nitroblue tetrazium (NBT) assay.
- * Evaluation of antibody-mediated effects on tachyzoite infectivity and NBT reduction.
- * Analysis of 1-day Toxoplasma's impact on specific antibody titers in human sera using the dye test.
Main Results:
- * 1-day Toxoplasma exhibited significantly higher infectivity and replication within macrophages compared to 2-day Toxoplasma.
- * 1-day Toxoplasma were more resistant to the killing activity of activated macrophages.
- * Macrophage respiratory burst was not triggered by 1-day Toxoplasma, but antibody opsonization reduced NBT.
- * Antibody coating did not significantly decrease 1-day Toxoplasma infectivity, unlike for 2-day Toxoplasma.
- * The dye test showed a 5-fold decrease in human serum antibody titers when using 1-day Toxoplasma.
Conclusions:
- * Toxoplasma tachyzoites harvested at 24 hours post-infection possess enhanced virulence characteristics.
- * 1-day Toxoplasma represent a valuable tool for investigating parasite virulence factors and host cell antimicrobial mechanisms.
- * The differential interaction of tachyzoite age with host immunity highlights the complexity of Toxoplasma pathogenesis.