Detection and characterization of soluble CD93 released during inflammation.
BACKGROUND
CD93 is a cell surface glycoprotein that is required for efficient engulfment of apoptotic cells via an unknown mechanism. Recently, it was demonstrated that CD93 is proteolytically cleaved from the surface of activated human monocytes and neutrophils in response to inflammatory signals in vitro and that a soluble form of CD93 (sCD93) exists in human plasma.


OBJECTIVE
The objective of this study was to examine the relationship among production of sCD93, inflammation, and engulfment of apoptotic cells.


METHODS
Sterile peritonitis was induced in C57BL/6 mice, and lavage fluid was analyzed for presence of sCD93 by ELISA and Western blot. Cellular infiltrate was assessed by flow cytometry and analyzed for its capacity to shed CD93 in vitro. Peritoneal lavage fluid (PLF) was examined for its ability to regulate engulfment of apoptotic cells.


RESULTS
There was an 8.9-fold increase in sCD93 following induction of peritonitis. Macrophages accounted for the majority of infiltrating leukocytes into the peritoneum when sCD93 levels were highest. Inflammatory peritoneal macrophages constitutively shed CD93 in vitro suggesting that this cell type contributes to elevated levels of sCD93 in vivo. Inflammatory PLF from wild-type mice containing elevated sCD93 significantly enhanced engulfment of apoptotic cells in vitro when compared to inflammatory fluid from CD93-deficient mice.


CONCLUSIONS
These data demonstrate that inflammation triggers release of sCD93 in vivo, identify the inflammatory macrophage as a source of sCD93, and provide insight into the mechanism by which CD93 contributes to engulfment of apoptotic cells.
Greenlee
Mallary C
MC
Department of Biological Sciences, Eck Institute for Global Health, University of Notre Dame, IN 46556, USA. mgreenle@nd.edu
Sullivan
Sarah A
SA
Bohlson
Suzanne Slater
SS
D000818:Animals; D017209:Apoptosis / Q000276:immunology; D002460:Cell Line; D006801:Humans; D007249:Inflammation / Q000276:immunology*; D008264:Macrophages / Q000166:cytology / Q000276:immunology; D008562:Membrane Glycoproteins / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010538:Peritonitis / Q000276:immunology; D011951:Receptors, Complement / Q000276:immunology*
D008562:Membrane Glycoproteins; D011951:Receptors, Complement; C032402:complement 1q receptor