CD8+ T cell recognition of cyst-derived antigen during chronic CNS infection with Toxoplasma gondii 4698

Abstract Description Toxoplasma gondii parasites establish persistent infection within neurons by forming cysts containing latent form bradyzoites. Given the limited MHC-I expression by neurons, it was previously thought that both neurons and cysts were protected from T cell recognition. However, neurons isolated from the brains of infected mice and cyst-containing neurons were found to express MHC-I, indicating that neurons can present to T cells. Recent work suggests that a cyst-derived antigen is recognized by CD8+ T cells – but it was unclear how such antigens would get beyond the cyst wall to enter the MHC-I pathway. To explore if cyst antigens can be transported beyond the cyst wall for direct presentation by neurons, we generated a BAG1-GRA6-SIINFEKL (BAG1-GRA6) parasite line in which there is bradyzoite-specific expression of the SIINFEKL T cell epitope linked to GRA6, a secreted dense granule protein hypothesized to be transported across the cyst wall. BAG1-GRA6 antigen was detected within the cytoplasm of in-vitro infected cells, indicating that cyst antigens can get beyond the cyst wall. To determine if the BAG1-GRA6 antigen is encountered by T cells within the brain, TCR reporter Nur77-GFP-OT-Is were transferred into and then recovered from the brains of BAG1-GRA6-infected mice. A proportion of OT-Is were found to be Nur77-GFP+, indicating that these T cells recognized cyst antigen within the site. Future studies will determine the identity of the cell(s) presenting cyst antigen. Funding Sources NIH 5-R01-AI-157247-04 NIH T32 CA009140 Topic Categories Neuroimmunology (NEUR)