a, A small fraction of UNC93B1 resides in endosomes compared to the ER. Subcellular fractionation of RAW macrophages expressing TLR7–HA and UNC93B1–Flag was performed by density-gradient centrifugation. The distribution of calnexin (ER), LAMP1 (late endosomes and lysosomes), UNC93B1–Flag and TLR7–HA across fractions was measured by immunoblot. Data are representative of three independent experiments. b, Workflow for isolation of phagosomes from RAW macrophages and purification of UNC93B1–Flag complexes from phagosome lysates.