Recurrent ocular toxoplasmosis is associated with interferon-gamma deficiency possibly due to genetic origin

Objective: Ocular toxoplasmosis (OT) can cause posterior uveitis; causes of recurrent OT are not well understood. We explored clinical, immunological and genetic properties associated with recurrent OT.

Methods and analysis: A recurrent OT patient population (n=9) was identified. Clinical history, ophthalmological findings and immunological properties were assessed. B and T cell immunophenotyping including interferon-gamma (IFN-γ) responses were analysed. An analysis of 592 immunodeficiency genes was performed.

Results: The patients experienced 2-7 OT episodes (average 3.7). The first episode occurred at an average of 23.8 (SD 10.1) years of age. All patients had anterior uveitis, vitritis and various fundus lesions of OT. The patients had lymphocyte maturation abnormalities; the proportion of naive CD4⁺CD45RA⁺CCR7⁺ T cells was high in 5/9 cases, and the percentage of CD4⁺CD45RA^-CCR7^- T effector memory cells was reduced in 7/9 cases. An increased percentage of CD19⁺CD38^lowCD21^low activated B cells was observed in 5/9 cases. IFN-γ response was reduced in CD4⁺ (8.45±4.17 vs 21.27±11.0, p=0.025) and CD8⁺ (39.0±9.9 vs 18.1±18.1, p=0.017) T cells. Genetic analysis revealed several potentially harmful variants in immunologically active ERCC3, MANBA, IRF4, HAVCR2, CARMIL2, CD247, MPO, C2 and CD40 genes.

Conclusion: Our recurrent OT cases had deviations in lymphocyte maturation and IFN-γ responses possibly caused by genetic reasons. However, limitations of our study include failure to identify uniform genetic mechanisms. In addition, we cannot rule out the possibility that the immunological abnormalities can be triggered by chronic toxoplasmosis. Despite the limitations, our findings contribute to the understanding of ocular immunity and development of recurrent OT.