Background: STAT6 plays a crucial role in M2a macrophage polarization in vitro and these cells mediate mucosal healing in an acute model of TNBS-colitis through the expression of Wnt ligands . We have recently reported that STAT6 deficiency favours fibrosis in a murine model of TNBS colitis  and we aim to characterize here the functional relevance of the macrophage phenotype in fibrosis development.
Methods: WT or STAT6(−/−) mice were given TNBs (0.5, 0.5, 0.75, 0.75, 1, and 1 mg, intrarectally) or saline weekly and they were sacrificed 3, 5 or 7 weeks after the first TNBs administration. The percentage of CD206, CD16, and CD86 positive cells was analyzed by flow cytometry in F4/80+ macrophages isolated from the intestinal mucosa. The mRNA expression of Wnt ligands was evaluated in F4/80+ CD16+ macrophages isolated from the mucosa, 7 weeks after the first TNBs administration and results are expressed as fold induction vs vehicle-treated mice. Data are expressed as mean ± SEM with n≥8 in all groups (*p<0.05).
Results: TNBs increased the percentage of CD206 positive macrophages in the mucosa of TNBS-WT animals while it failed to do that in TNBS-STAT6(−/−) mice. The percentage of CD16 positive macrophages increased in a time-dependent manner only in the mucosa of STAT6(−/−)-TNBS-treated mice. The number of CD86+ cells was similar in TNBS-WT and TNBS-STAT6(−/−) mice.
In CD16+ macrophages isolated from TNBS-STAT6(−/−) mice the mRNA expression of canonical and non-canonical Wnt ligands was significantly increased compared with cells isolated from TNBS-WT mice.
Conclusions: An increased percentage of M2c macrophages which exhibited an increased expression of Wnt ligands is detected in the mucosa of TNBS-STAT6 knockout mice and it could mediate the increased fibrosis detected in these animals.
 Cosín-Roger J, Ortiz-Masiá D, Calatayud S, Hernández C, Esplugues JV, Barrachina MD., (2016), The activation of Wnt signaling by a STAT6-dependent macrophage phenotype promotes mucosal repair in murine IBD., Mucosal Immunol. 2016 Jul;9(4):986–98. doi: 10.1038/mi.2015.123.
 P. Salvador, (2016), STAT6 deficiency alters macrophage polarization and promotes fibrosis in a murine model of chronic inflammation. ECCO2016