LDs and innate immunity. (A) Six examples highlighting key roles of LDs in innate immunity. LDs are emerging as key organelles in innate immunity. The figure includes selected examples of the multifaceted roles of LDs during host defense. Details and references are in Box 3. (B–D) LDs interact with bacteria in infected cells. HMD macrophages from healthy donors were infected with E. coli for 4 h and analyzed by transmission electron microscopy. B–D are unpublished images from Robert Parton. (B) Serial blockface scanning electron microscopy data reconstruction showing an infected macrophage. The plasma membrane (pink), bacteria (blue), and LDs (green) in the 3D dataset have been colored and projected onto a single image. (C and D) Representative images of the LD–bacteria interaction are pseudocolored blue (bacteria), green (LD), red (E. coli outer and inner membranes and periplasm), and yellow (phagolysosomal membrane). The analysis reveals numerous contacts between LDs and E. coli. In the LD–E. coli contact sites, the LD monolayer (containing LD proteins) produced an apparent discontinuity in the phagolysosomal membrane (yellow) and probably interacted with the bacterial outer membrane (contacts are indicated with red arrows). FA, fatty acid; ss, single-stranded.