Is Toxoplasma gondii-secreted Protein With an Altered Thrombospondin Repeat (TgSPATR) a Potential Candidate for Immunisation? An Immunoinformatics-Based Analysis.

BACKGROUND: Toxoplasmosis is a widespread zoonotic disease that poses risks to pregnant women and immunocompromised individuals. Despite considerable efforts, no licensed vaccines are currently available for humans or animals. Rational vaccine design increasingly relies on immunoinformatics approaches to identify immunodominant epitopes and key immunological features. OBJECTIVES: This study aimed to characterise the Toxoplasma gondii-secreted protein with an altered thrombospondin repeat (TgSPATR) using immunoinformatics tools to evaluate its suitability as a vaccine candidate. METHODS: A comprehensive panel of bioinformatics servers was used to predict allergenicity, solubility, antigenicity, secondary and tertiary structures, post-translational modification (PTM) regions, and B- and T-cell epitopes, followed by in silico immune simulation. RESULTS: TgSPATR consists of 534 amino acids with an estimated molecular weight of ∼57 kDa. The aliphatic index (65.71) and GRAVY score (-0.507) indicate moderate thermostability and an overall hydrophilic nature. Additionally, a total of 120 PTM sites were predicted, including phosphorylation, O- and N-glycosylation, and palmitoylation sites. Secondary structure analysis (GOR IV, SOPMA, and NetSurfP-3.0) revealed a predominance of random coils. Moreover, multiple servers (BcePred, SVMTriP, ABCpred, IEDB, ElliPro, and CTLpred) identified several high-scoring B- and T-cell epitopes capable of binding MHC class I and II molecules. According to SAVES v6.1, 74.1% and 93.8% of the residues of the initial and refined 3D models were located in favoured regions, indicating improved structural quality after refinement. In line with this, the ERRAT score also increased from 89.557 to 95.046. TgSPATR was predicted to be immunogenic and non-allergenic. Finally, virtual immune simulation using the C-ImmSim server showed that TgSPATR can elicit both humoral and cellular immune responses following three injections. CONCLUSIONS: This study provides foundational evidence that TgSPATR possesses key immunogenic properties and may serve as a promising vaccine candidate against acute and chronic toxoplasmosis. Nonetheless, wet-lab experiments are required to validate these computational findings.