Phosphatidylserine expression and phagocytosis of apoptotic thymocytes during differentiation of monocytic cells.
Expression of phosphatidylserine (PS) on the surface of both macrophages and their apoptotic targets is required for efficient phagocytosis. Monocytes, the precursors of macrophages, do not express PS on their surface and do not efficiently phagocytose apoptotic cells. We report here that PS appears on the surface of both human monocytic U937 cells and primary human monocytes as they differentiate in culture and acquire the ability to phagocytose apoptotic thymocytes. Phagocytosis was blocked by pretreating either the apoptotic target or the phagocyte with annexin V to mask PS and was CD14-dependent. Expression of PS, like other events characteristic of differentiating monocytes such as Mac-1 expression, was independent of the agent used to induce differentiation and was insensitive to the addition of caspase inhibitors. These results demonstrate that PS is expressed on monocytes as part of their differentiation program and is independent of apoptosis.
Callahan
Melissa K
MK
Department of Biochemistry and Molecular Biology, Penn State University, University Park, PA 16802, USA.
Halleck
Margaret S
MS
Krahling
Stephen
S
Henderson
Andrew J
AJ
Williamson
Patrick
P
Schlegel
Robert A
RA
D017209:Apoptosis / Q000502:physiology*; D002454:Cell Differentiation; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000502:physiology; D009000:Monocytes / Q000166:cytology* / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology*; D010718:Phosphatidylserines / Q000096:biosynthesis*; D013601:T-Lymphocytes / Q000166:cytology* / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D020298:U937 Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology
D010718:Phosphatidylserines; D013755:Tetradecanoylphorbol Acetate