Autophagy in CD11c⁺ cells is required for the development of protective immunity to T. gondii infection

Autophagy is a lysosomal degradation pathway that maintains cellular homeostasis by sequestering cytosolic materials and targeting them to lysosomes. Proteins in this classical autophagy pathway are also important for many other cellular functions including phagocytosis, inflammatory signaling, control of intracellular pathogens, and antigen presentation. One cassette of these autophagy proteins, which includes the ATG5-ATG12-ATG16L1 complex, has been shown to be critical in targeting IFN-γ mediated effectors to the T. gondii parasitophorous vacuole (PV) to disrupt the PV and kill the parasite. Conditional deletion of any of the genes from this ATG5-ATG12-ATG16L1 complex in myeloid cells using LysM-Cre mice (LysM x ATG-flox) has shown this protein complex is required for infected macrophages and monocytes to kill the parasite and control acute T. gondii infection in vivo. To investigate the role of this autophagy protein complex in conventional dendritic cells (cDC) during T. gondii infection, ATG5-flox and ATG16L1-flox mice were bred with CD11c-Cre mice. Surprisingly, deletion of autophagy proteins in CD11c-Cre expressing cells also resulted in increased host susceptibility during the acute phase of T. gondii infection. Lineage tracing of CD11c-Cre expression showed that Cre expression is not isolated to cDCs and occurs in a subpopulation of myeloid precursors as well as in all inflammatory monocytes and macrophages. Deletion of the ATG16L1 protein was equivalent in both LysM-ATG16L1 and CD11c-ATG16L1 bone marrow-derived macrophages. Functionally, CD11c-ATG16L1 macrophages failed to localize the IFN-γ mediated effectors to the PV, which resulted in uncontrolled parasite replication. Additionally, ATG16L1 protein expression in CD11c⁺ cells is required for the development of a protective CD8⁺ T cell response following vaccination with the non-replicating CPS strain of T. gondii. While LysM-ATG16L1 and CD11c-ATG16L1 mice generate an impaired T cell response to CPS immunization, only CD11c-ATG16L1 mice succumb to rechallenge with the virulent RH strain of the parasite. Ongoing work is focusing on the mechanistic difference in the response to immunization between LysM-ATG16L1 and CD11c-ATG16L1 mice.