Type 1 and Type 2 Toxoplasma Gondii Strains: Differences in Growth and Invasive Abilities

Abstract

Purpose:: Toxoplasma gondii is responsible for the majority of infectious uveitis. The pathogenesis of the ocular infection is not well understood.Recurrences of the retinal lesion are thought to be due to ability of Toxoplasma gondii to cross cellular membranes. It is also possible that systemic infection leads to ocular recurrences therefore this parasite may have the ability to cross the basement membranes of blood vessels. The purpose of this study is to demonstrate in vitro the differences in the growth and aggressiveness of different strains of Toxoplasma gondii. In addition invasive assays were performed to evaluate the ability of these parasites to cross a basement membrane.

Methods:: Four different strains of human Toxoplasma gondii were cultured: a type 1 and type 2 strain isolated from patients in France; a type 2 strain from a US patient and a type 1 congenital strain from France. All of them were grown on a fibroblast layer and the growth of the samples were observed and documented. The relative ability of the four strains to destroy fibroblast layers was assayed using a modified MTT proliferation assay. In addition, an invasive assay with a modified boyden chamber using matrigel artificial basement membranes was performed. Fibroblasts were grown to confluence in the bottom well and the four strains of toxoplasma gondii were seeded into the top well of the boyden chambers. The matrigel was then imaged to assess the presence of invading parasites.

Results:: All samples of Toxoplasma gondii grew well in vitro when a confluent fibroblast layer was present. Differences among the four strains were demonstrated with the proliferation assay: the type 1 congenital strain yielded the most death of fibroblasts followed by the type 1 strain from the USA. Both the type 2 strains, whether from the USA or France, were shown to be the least aggressive. The presence of Toxoplasma gondii was seen invading in all of the matrigel artificial basement membranes.

Conclusions:: The four strains of Toxoplasma gondii were easily cultured using fibroblasts,although differed in their ability to destroy fibroblasts.Both type 1 strains being more aggressive than type 2 strains. To the best of our knowledge this is the first time that the invasion of an artificial basement membrane by Toxoplasma gondii has been demonstrated. Further studies to correlate this ability to the pathogenesis of ocular recurrences will be undertaken.

Keywords: toxoplasmosis • inflammation