SMPD1 and infection: Because ceramide generated by aSMase is a precursor of CERK-derived C1P (Fig. 2A), CERK is localized in the TGN (56), delivery of TGN-derived vesicles enriched in ceramide and sphingomyelin into the ApV is critical for A. phagocytophilum infection cycle progression (25), and disrupting ceramide generation by inhibiting aSMase halts the infection cycle (66, 67), C1P levels were examined in infected versus uninfected cells using ultra high performance-liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS).