[toggle_content title=”Abstract”]The contribution of innate immunity to inflammatory bowel disease (IBD) remains an area of intense interest. Macrophages (MØ) and dendritic cells (DC
) are considered important factors in regulating the onset of IBD. The goal of this study was to determine if intestinal mononuclear phagocytes (iMNP) serve a pathological or protective role in dextran sulfate sodium (DSS)-induced colitis in mice. Using a conditional MØ/DC
depletion transgenic mouse line—MØ Fas-induced apoptosis— to systemically deplete iMNP, DSS colitis histopathology was shown to be more severe in MØ/DC
-depleted compared with MØ/DC
-intact mice. Similarly, localized iMNP depletion by clodronate- encapsulated liposomes into C57BL/6, BALB/c, and CB.17/SCID mice also increased DSS colitis severity, as indicated by increased histopathology, weight loss, rectal bleeding, decreased stool consistency, and colon length compared with MØ/DC
-intact, DSS-treated mice. Histology revealed that iMNP depletion during DSS treatment led to increased neutrophilic inflammation, increased epithelial injury, and enhanced mucin depletion from Goblet cells. iMNP depletion did not further elevate DSS-induced expression of TNF- and IFN- mRNA but significantly increased expression of CXCL1 chemokine mRNA. Myeloperoxidase activity was increased in colons of MØ/DCdepleted, DSS-treated mice, compared with DSS alone, coincident with increased neutrophil infiltration in diseased colons. Neutrophil depletion combined with MØ/DC
depletion prevented the increase in DSS colitis severity compared with MØ/DC
depletion alone. This study demonstrates that iMNP can serve a protective role during development of acute colitis and that protection is associated with MØ/DC
-mediated down-regulation of neutrophil infiltration.[/toggle_content] [toggle_content title=”Clodronate Liposome Parameters”] [custom_table]
||Total Lipid Concentration
||Lipid Mole %
[/custom_table] [/toggle_content] [toggle_content title=”Animals and Dosing”] [custom_table]
|C57BL/6, BALB/c, CB.17/SCID, MaFIA female mice, 5-8 w
[/custom_table] [/toggle_content] [toggle_content title=”Notes”]
- Liposome prep method cited — van Rooijen N, Sanders A. Liposome mediated depletion of macrophages: mechanism of action, preparation of liposomes and applications. Journal of Immunological Methods. 1994 Sep 14;174(1–2):83–93.
- Mice were anesthesized with an i.p. injection of 200 µl 2.5% Avertin. 100 µl clodronate liposomes were injected intrarectally using a micropipette. No other details were provided; it is not clear whether a Pipetman-type polycarbonate tip or a glass capilllary type micropipette was used.
- Authors note that depletion was minimal in the more proximal regions of the colon.
- Authors further state that intrarectal injection of control liposomes resulted in a partial reduction of total colonic MΦ and could effect the physiology of the remaining colonic MΦ (data not shown). Therefore, they chose not to include empty liposome controls.
[/toggle_content] [toggle_content title=”Results”]
- A single intrarectal treatment (MaFIA mice) with clodronate liposomes resulted in a 92% of the MΦ in the descending colon at 24 h post-treatment.
- Lesser effects were observed in the transverse and ascending colon, however no depletion was observed in the bone marrow and peritoneum.
- C57BL/6, BALB/c and CB.17/SCID female mice were injected intrarectally with 100 µl clodronate liposomes on days -1, +1, +3 and +5 days while dextran sodium sulfate (DSS) was added to their drinking water beginning at day 0. On day 7 (day 5 for CB.17/SCID) the % of CD45+Ly-6G-CD11b+ MΦ was about half the control values indicating a relatively rapid repopulation of colonic MΦ.
- Although the different mouse strains demonstrated different levels of disease responses, all strains had significantly more severe disease activity overall when MΦ were depleted.
- Spleens and mestenteric lymph nodes were cultured to determine if MΦ depletion resulted in a release of bacteria from colon, but little or no bacteria were found.
- MΦ depletion correlated to an increase in chemokine CXCL1 and neutrophils, but not other cytokines.
- Concurrent neutrophil depletion prevented the increase in disease severity resulting from MΦ depletion.
- Given that control liposomes had a significant effect on colonic MΦ and that the decrease in these MΦ was not likely due to MΦ killing by the liposomes, we wonder what results control liposomes would have produced. Could the increase in neutrophil activity be the result of MΦ killing and not exclusively due to the absence of macrophages?