Autophagy is Required for Control of Ocular Toxoplasmosis

Abstract

Purpose: : Autophagy degrades pathogens in vitro. However, it is not known whether adaptive immunity that develops during an infection utilizes autophagy for in vivo protection. We studied the in vivo relevance of autophagy by using an animal model of ocular toxoplasmosis.

Methods: : Mice deficient in CD40, the autophagy molecules Beclin 1 or Atg7 as well as wild type controls were infected with Toxoplasma gondii. Ocular histopathology and parasite load were examined. Protein and mRNA levels of autophagy molecules as well as IFN-γ, TNF-α and NOS2 were examined by immunoblot and real time PCR. Generation of T. gondii specific T cell responses as well as microglia anti-T. gondii activity were examined.

Results: : We report that CD40 upregulates the autophagy molecule Beclin 1 in microglia and triggers autophagic killing of Toxoplasma gondii. CD40^-/- mice failed to upregulate Beclin 1 in microglia/macrophages in vivo. Autophagy-deficient Beclin 1^+/- mice and CD40^-/- mice exhibited impaired autophagic killing of T. gondii and were susceptible to ocular and cerebral toxoplasmosis despite upregulation of IFN-γ/TNF-α, NOS2 and the generation of T. gondii-specific T cell response. Mice lacking ATG7 in macrophages/ microglia were also susceptible to toxoplasmosis. CD40 triggered T. gondii killing by down-regulating p21, a protein that degrades Beclin 1.

Conclusions: : These studies provide the first evidence that adaptive immunity utilizes autophagy for in vivo protection against a pathogen.

Keywords: microglia • immunomodulation/immunoregulation • microbial pathogenesis: experimental studies