Biogenesis of Afipia-containing phagosomes in non-professional phagocytes.

Afipia felis is a Gram-negative alpha-proteobacterium, a rare cause of human cat scratch disease (CSD), and likely a pathogen of amoeba. Here, we show that various members of the genus Afipia attach to and are taken up by various non-professional phagocytic mammalian cells (epithelial CHO, endothelial EA.hy926, epithelial HeLa, epithelial INT407 cells, endothelial HMEC-1, endothelial HUVEC, and fibroblast L929 cells). However, only A. felis was able to do this efficiently. Invasion depended on a functional actin cytoskeleton and much less on microtubule dynamics. Bacteria were slowly taken up into HMEC-1 (and HUVEC) via pocket-like structures and they resided within membrane-surrounded phagosomes. While A. felis was found in a non-canonical endocytic compartment in macrophage cells, Afipia-containing phagosomes in HMEC-1 were transiently positive for early endosomal EEA1 and then became and remained positive for lysosome-associated membrane protein-1 (LAMP1) and the proton-pumping ATPase, suggesting undisturbed, albeit slowed, phagosome biogenesis in these cells. Similarly, at 24h of infection, most phagosomes in HeLa, INT407, HUVEC and in EA.hy926 cells were positive for LAMP1. In summary, A. felis enters various non-professional phagocytes and its compartmentation differs between macrophages and non-professional phagocytes.