AI Article Synopsis

  • IL-25 is a Th2-related cytokine that reduces inflammation in colitis by promoting alternatively activated macrophages (AAMs), but the mechanism of this effect was previously unclear.
  • The study revealed that IL-25 enhances AAM-related markers in macrophages and transfers AAMs from IL-25-treated mice reduced colitis severity in TNBS-induced colitis models.
  • Although IL-25 increases cytokines like IL-4, IL-13, and TGF-β1 that promote AAM differentiation, blocking these cytokines did not stop IL-25's effect on AAM expression, confirming that IL-25's anticolitic role involves AAM induction.

Article Abstract

Background: Interleukin (IL)-25, a Th2-related factor, inhibits the synthesis of inflammatory cytokines by macrophages and attenuates experimental colitis in mice. The mechanism underlying the counterregulatory effect of IL-25, however, remains unknown. Since Th2-cytokines can abrogate inflammatory pathways by inducing alternatively activated macrophages (AAMs), we evaluated whether AAMs are involved in the IL-25-mediated anticolitic effect.

Methods: AAM-related markers were evaluated in peritoneal and lamina propria mononuclear cells of mice with or without 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced colitis treated with IL-25 and/or neutralizing IL-4, IL-13, and transforming growth factor beta 1 (TGF-β1) antibodies. Peritoneal AAMs induced in vivo by injecting mice with IL-25 were transferred to mice with TNBS colitis. Finally, we assessed the in vitro effect of IL-25 on the alternative activation of peritoneal F4/80+ cells.

Results: IL-25 enhanced the expression of AAM-related markers in F4/80(+) cells infiltrating the peritoneum and colon of naïve and colitic mice. Peritoneal F4/80(+) cells isolated from IL-25-treated mice reduced the severity of TNBS colitis when injected intraperitoneally to recipient mice. Since IL-25 did not directly induce AAM in vitro and in vivo in mice, IL-25 administration enhanced the expression of IL-4, IL-13, and TGF-β1, which are known to promote AAM differentiation, we finally assessed whether such cytokines were involved in the IL-25-driven AAM induction. Blockade of IL-4, IL-13, and TGF-β1 with neutralizing antibodies in mice did not inhibit the stimulatory effect of IL-25 on AAM gene expression.

Conclusions: The IL-25-mediated anticolitic effect is associated with induction of AAMs, a subset of macrophages with antiinflammatory properties.

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http://dx.doi.org/10.1002/ibd.21799DOI Listing

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