The regulatory role of IL-10 in maintaining asymptomatic Toxoplasmosis mediated by PD-1 signaling in humans and PFD1 in cats

Background: Toxoplasmosis is a zoonotic infection triggered by Toxoplasma gondii, which in immunocompetent people often remains undetected, resulting in its overlooked significance in the epidemiological record of infected cats and humans. Aim: The present study was conducted to determine immunological markers, including IL-10, IL-17, and their possible role in asymptomatic infection and their connection with Bradyzoite Formation Deficient 1 (PFD1) among cats and PD-1/PD-L1 signaling pathway among humans. Methods: This study was performed on one hundred cats and one hundred and fifty cat owners from fifteen veterinary clinics in Basrah. An ELISA test was performed to investigate circulating T. Gondii antigens alongside IL-10 and IL-17 levels in all investigation subjects. Quantitative real-time RT-PCR was employed to assess the gene expression of feline PFD1 and human PD-1/PD-L1. Clinical evaluations indicated that none of the subjects exhibited symptoms of toxoplasmosis. Conventional statistical methods were applied to contrast the genetic characteristics between infected and non-infected groups. Results: The seroprevalence of toxoplasmosis was 46% (69/150) in humans and 71% (71/100) in cats, respectively. Both infected humans and cats showed significantly elevated IL-10 levels alongside reduced IL-17 levels (p < 0.001). Moreover, gene expression analysis also revealed an increase in feline PFD1 in infected cats and PD-1 in infected humans (p < 0.001), indicating an immunosuppressive profile that could promote parasite persistence. Conclusions: Both human and feline asymptomatic toxoplasmosis are related to an increase in anti-inflammatory response, Ll-10 mediated, as well as perturbation of immunogenic balance by the PFD1 and PD-1/PD-L1 pathways.