Polymicrobial sepsis enhances clearance of apoptotic immune cells by splenic macrophages.
BACKGROUND
Macrophage phagocytosis of apoptotic cells induces an anti-inflammatory macrophage phenotype. Immune cell apoptosis is widespread in sepsis; however, it is unknown whether sepsis alters the capacity of macrophages to clear this expanded population. We hypothesize that sepsis will enhance splenic macrophage phagocytosis of apoptotic immune cells, potentially contributing to immunosuppression.


METHODS
Sepsis was induced in C57BL/6J mice by cecal ligation and puncture (CLP). Apoptosis was induced in mouse thymocytes by dexamethasone incubation. At multiple time points after CLP/sham, splenic and peritoneal macrophages were isolated, plated on glass coverslips, co-incubated with apoptotic thymocytes, and fixed and the coverslips were then Giemsa stained. Splenic macrophages were also isolated 48 hours after CLP/sham, stained with the red fluorescent dye PKH26, and co-incubated with green fluorescent dye CFSE-stained apoptotic thymocytes and then coverslips were fixed and counterstained with DAPI. The macrophage phagocytic index (PI) was calculated for both staining methods.


RESULTS
The PI of CLP splenic macrophages was significantly higher than sham by 24 hours, and this difference was sustained through 48 hours.


CONCLUSIONS
Studies suggest that apoptotic cell clearance leads to an anti-inflammatory macrophage condition, which together with our findings in septic macrophages, may point at a process that contributes to septic immune suppression.
Swan
Ryan
R
Division of Surgical Research, Department of Surgery, Brown University School of Medicine, Providence, RI, USA.
Chung
Chun-Shiang
CS
Albina
Jorge
J
Cioffi
William
W
Perl
Mario
M
Ayala
Alfred
A
D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002432:Cecum / Q000293:injuries / Q000382:microbiology; D005434:Flow Cytometry; D005452:Fluoresceins; D005456:Fluorescent Dyes; D008026:Ligation; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000276:immunology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D010587:Phagocytosis / Q000276:immunology*; D018805:Sepsis / Q000276:immunology*; D013154:Spleen / Q000166:cytology / Q000276:immunology; D013388:Succinimides; D013601:T-Lymphocytes / Q000166:cytology / Q000276:immunology*; D014951:Wounds, Stab
C087165:5-(6)-carboxyfluorescein diacetate succinimidyl ester; D005452:Fluoresceins; D005456:Fluorescent Dyes; D013388:Succinimides
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