Association of a NOD2 gene polymorphism and T-helper 17 cells with presumed ocular toxoplasmosis

Retinochoroiditis manifests in patients infected with Toxoplasma gondii. Here, we assessed 30 sibships and 89 parent/case trios of presumed ocular toxoplasmosis (POT) to evaluate associations with polymorphisms in the NOD2 gene. Three haplotype-tagging single-nucleotide polymorphisms (tag-SNPs) within the NOD2 gene were genotyped. The family-based association test showed that the tag-SNP rs3135499 is associated with retinochoroiditis (P = .039). We then characterized the cellular immune response of 59 cases of POT and 4 cases of active ocular toxoplasmosis (AOT). We found no differences in levels of interferon γ (IFN-γ) and interleukin 2 produced by T-helper 1 cells when comparing patients with AOT or POT to asymptomatic individuals. Unexpectedly, we found an increased interleukin 17A (IL-17A) production in patients with POT or OAT. In patients with POT or AOT, the main cellular source of IL-17A was CD4(+)CD45RO(+)T-bet(-)IFN-γ(-) T-helper 17 cells. Altogether, our results suggest that NOD2 influences the production of IL-17A by CD4(+) T lymphocytes and might contribute to the development of ocular toxoplasmosis.

Evidence for associations between the purinergic receptor P2X(7) (P2RX7) and toxoplasmosis

Congenital Toxoplasma gondii infection can result in intracranial calcification, hydrocephalus, and retinochoroiditis. Acquired infection is commonly associated with ocular disease. Pathology is characterized by strong pro-inflammatory responses. Ligation of ATP by purinergic receptor P2X₇, encoded by P2RX7, stimulates pro-inflammatory cytokines and can lead directly to killing of intracellular pathogens. To determine whether P2X₇ plays a role in susceptibility to congenital toxoplasmosis, we examined polymorphisms at P2RX7 in 149 child/parent trios from North America. We found association (FBAT Z scores ±2.429; P= 0.015) between the derived C(+)G(−) allele (f= 0.68; OR= 2.06; 95% CI: 1.14–3.75) at SNP rs1718119 (1068T>C; Thr-348-Ala), and a second synonymous variant rs1621388 in linkage disequilibrium with it, and clinical signs of disease per se. Analysis of clinical sub-groups showed no association with hydrocephalus, with effect sizes for associations with retinal disease and brain calcifications enhanced (OR=3.0 to 4.25; 0.004<P<0.009) when hydrocephalus was removed from the analysis. Association with toxoplasmic retinochoroiditis was replicated (FBAT Z scores ±3.089; P= 0.002) in a small family-based study (60 families; 68 affected offspring) of acquired infection in Brazil, where the ancestral T(+) allele (f= 0.296) at SNP rs1718119 was strongly protective (OR= 0.27; 95% CI: 0.09–0.80). (Words 194)

Candidate gene analysis of ocular toxoplasmosis in Brazil: evidence for a role for toll-like receptor 9 (TLR9)

Toxoplasma gondii infection is an important mediator of ocular disease in Brazil more frequently than reported from elsewhere. Infection and pathology are characterized by a strong proinflammatory response which in mice is triggered by interaction of the parasite with the toll-like receptor (TLR)/MyD88 pathway. A powerful way to identify the role of TLRs in humans is to determine whether polymorphisms at these loci influence susceptibility to T. gondii-mediated pathologies. Here we report on a small family-based study (60 families; 68 affected offspring) undertaken in Brazil which was powered for large effect sizes using single nucleotide polymorphisms with minor alleles frequencies > 0.3. Of markers in TLR2, TLR5 and TLR9 that met these criteria, we found an association Family Based Association Tests [(FBAT) Z score = 4.232; p = 1.5 x 10-5; p corrected = 1.2 x 10-4] between the C allele (frequency = 0.424; odds ratio = 7; 95% confidence interval 1.6-30.8) of rs352140 at TLR9 and toxoplasmic retinochoroiditis in Brazil. This supports the hypothesis that direct interaction between T. gondii and TLR9 may trigger proinflammatory responses that lead to severe pathologies such as the ocular disease that is associated with this infection in Brazil.