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Cynthia A. Cordeiro, Fernando Orefice, Jeroen Saeij, Lucy Young; Toxoplasma Strain-specific Modulation Of Host Immune Signaling Pathways. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2962.
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© ARVO (1962-2015); The Authors (2016-present)
: Toxoplasma gondii has a population structure that can be roughly divided into 11 haplotypes. Strains vary in prevalence and disease outcomes, but the genetic cause of these differences is largely unknown. We examined strain differences, by immunofluorescence assay, in the modulation of two important immune signaling pathways, the host NF-kB and STAT signaling pathways.
We used at least one representative strain for all 11 haplotypes. We used a Pru strain expressing a type I copy of ROP16 and a Pru strain with the GRA15 gene removed. We also used a RH strain with the ROP16 gene removed by double homologous recombination and a RH strain expressing a type II copy of GRA15. Parasites were incubated for 18 hours on monolayers of HFF cells grown on coverslips. The cells were then fixed, permeabilized and blocked. Coverslips were incubated with primary antibody overnight, and fluorescent secondary antibodies and Hoechst dye were used for antigen and DNA visualization, respectively. Coverslips were mounted on glass slides, and photographs were taken using NIS-Elements software and a digital camera connected to an inverted fluorescence microscope.
All strains activated STAT5/6, except type II strains. Using a type I ROP16KO strain, we confirmed that these phenotypes are indeed due to the ROP16. Similar but to a lesser extent than the type II strain, the type IV and type XI strains also induced nuclear translocation of NF-kB p65. All other strains tested did not induce significant nuclear translocation of NF-kB p65. Using a type II GRA15KO strain and type I strain expressing GRA15 from type II, we confirmed that the type II activation of NF-kB was due to GRA15.
These strain-specific modulations of host immune signaling pathways may explain differences in prevalence and disease outcomes. Interestingly, the type II strain, the world’s most prevalent strain, has a unique host cell activation profile of activating the NF-kB but not the STAT pathway. The strain-specific differences in host cell activation are correlated with their genotype at the GRA15 and ROP16 loci. Additionally, type IV strains, which have been associated with ocular toxoplasmosis, activated both STAT and NF-kB pathways.
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