Antibody-dependent xenophagy targets viruses and bacteria for destruction

Antibodies are known to prevent infection by binding to pathogens extracellularly and blocking their entry into cells. What is less well known is that a proportion of pathogens, called the persistent fraction, still succeed in entering cells despite the antibodies bound to their surface. Fortunately, all mammalian cells express a dedicated cytosolic antibody receptor called TRIM21 that intercepts these incoming antibody-bound pathogens as soon as they enter the cytosol. Once it has detected an infection event, TRIM21 uses its E3 ubiquitin ligase activity to target pathogens for degradation. Our early work showed that TRIM21-mediated neutralization was both a fast and efficient process, capable of causing the degradation of incoming viral particles within hours. What was less clear was how TRIM21 achieves this degradation. In a recent study, we reveal that TRIM21 mediates a system of selective autophagy to direct incoming pathogens into the lysosome.Abbreviations: TRIM21:Tripartite-motif containing protein 21; VCP: Valosin-Containing Protein. CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats; FACS: fluorescence activated cell sorting; GFP: green fluorescent protein; LC3: Microtubule-associated Protein 1 Light Chain 3; TBK1: TANK-binding kinase 1; FIP200: FAK family kinase-interacting protein of 200 kDa; ULK1: Unc-51-like autophagy activating kinase 1; PI3K: Phosphoinositide 3-Kinase; ATG: autophagy-related gene; TMEM41B: transmembrane protein 41B; VPS37A: Vacuolar Protein Sorting-Associated Protein 37A; RBSN: Rabenosyn-5; EPG5: Ectopic P-Granules 5 Autophagy Tethering Factor; NDP52: Nuclear Dot Protein 52; ADX: antibody-dependent xenophagy; p62/SQSTM1: Protein 62/ Sequestosome 1; LPS: Lipopolysaccharide.