Characterization of microbe-containing phagosomes using APEX2-based proximity labeling

Phagocytosis is the process by which myeloid phagocytes bind and internalize potentially dangerous microbes. During phagocytosis, innate immune receptors and the associated signaling adapters are localized to the maturing phagosome compartment. We used proximity labeling of phagosomal contents (PhagoPL) to identify proteins localizing to phagosomes containing model yeast and bacteria and identified programmed death-ligand 1 (PD-L1) as a protein that specifically enriches in phagosomes containing yeast. We found that PD-L1 directly binds to yeast upon processing in phagosomes and influences production of a subset of inflammatory cytokines and chemokines produced when macrophages encounter yeast.