ABSTRACTA core set of autophagy proteins is required for gamma interferon (IFN-γ)-mediated clearance ofToxoplasma gondiiin the mouse because of their control of several downstream effectors, including immunity-related GTPases (IRGs) and guanylate-binding proteins (GBPs). However, these effectors are absent (i.e., IRGs) from or nonessential (i.e., GBPs) in IFN-γ-activated human cells, raising the question of how these cells control parasite replication. Here, we define a novel role for ubiquitination and recruitment of autophagy adaptors in the strain-specific control ofT. gondiireplication in IFN-γ-activated human cells. Vacuoles containing susceptible strains ofT. gondiibecame ubiquitinated, recruited the adaptors p62 and NDP52, and were decorated with LC3. Parasites within LC3-positive vacuoles became enclosed in multiple layers of host membranes, resulting in stunting of parasite replication. However, LC3-positiveT. gondii-containing vacuoles did not fuse with endosomes and lysosomes, indicating that this process is fundamentally different from xenophagy, a form of autophagy involved in the control of intracellular bacterial pathogens. Genetic knockout of ATG16L or ATG7 reverted the membrane encapsulation and restored parasite replication, indicating that core autophagy proteins involved in LC3 conjugation are important in the control of parasite growth. Despite a role for the core autophagy machinery in this process, upstream activation through Beclin 1 was not sufficient to enhance the ubiquitination ofT. gondii-containing vacuoles, suggesting a lack of reliance on canonical autophagy. These findings demonstrate a new mechanism for IFN-γ-dependent control ofT. gondiiin human cells that depends on ubiquitination and core autophagy proteins that mediate membrane engulfment and restricted growth.IMPORTANCEAutophagy is a process of cellular remodeling that allows the cell to recycle senescent organelles and recapture nutrients. During innate immune responses in the mouse, autophagy is recruited to help target intracellular pathogens and thus eliminate them. However, the antimicrobial mediators that depend on autophagy in the mouse are not conserved in humans, raising the issue of how human cells control intracellular pathogens. Our study defines a new pathway for the control of the ubiquitous intracellular parasiteT. gondiiin human cells activated by IFN-γ. Recruitment of autophagy adaptors resulted in engulfment of the parasite in multiple membranes and growth impairment. Although susceptible type 2 and 3 stains ofT. gondiiwere captured by this autophagy-dependent pathway, type 1 strains were able to avoid entrapment.
The CD40-Autophagy Pathway Is Needed for Host Protection Despite IFN-Γ-Dependent Immunity and CD40 Induces Autophagy via Control of P21 Levels
