Lysosomal Lipases PLRP2 and LPLA2 Process Mycobacterial Multi-acylated Lipids and Generate T Cell Stimulatory Antigens

Abstract

Complex antigens require processing within antigen-presenting cells (APCs) to form Tcell stimulatory complexes with CD1 antigen-presenting molecules. It remains unknown whether lipids with multi-acylated moieties also necessitate digestion by lipases to become capable of binding CD1 molecules and stimulate Tcells. Here, we show that the mycobacterial tetra-acylated glycolipid antigens phosphatidyl-myo-inositol mannosides (PIM) are digested to di-acylated forms by pancreatic lipase-related protein 2 (PLRP2) and lysosomal phospholipase A2 (LPLA2) within APCs. Recombinant PLRP2 and LPLA2 removed the sn1- and sn2-bound fatty acids from the PIM glycerol moiety, as revealed by mass spectrometry and nuclear magnetic resonance studies. PLRP2 or LPLA2 gene silencing in APCs abolished PIM presentation to Tcells, thus revealing an essential role of both lipases invivo. These findings show that endosomal lipases participate in lipid antigen presentation by processing lipid antigens and have a role in Tcell immunity against mycobacteria.