It depends on what you mean by Mreg.  Two different macrophages subsets have been described as "regulatory"...although the use of this descriptor for any macrophages has been strongly advised against in an Immunity Perspective (Murray PJ 2014). 

An article in J Exp Med (Manrique SZ 2011) describing FoxP3-positive macrophages was retracted (see link for explanation).

Work from David Mosser's group has described regulatory macrophages that are far different that the FoxP3-type.  First they were described as macrophages treated with a combination of LPS and immune complexes (Sutterwala FS 1998) causing a loss of IL-12p70 production and a switch to IL-10 production.  Later, the "regulatory" phenotype was also seen in response to adenosine receptor signaling following activation with LPS (Cohen HB 2013a).  These "regulatory" macrophages are suggested to express high amounts of Arg1, Sphk1, HB-EGF, IL-10, TGFbeta, IL-33, and VEGF (Cohen HB 2013b).

http://ac.els-cdn.com/S1074761314002283/1-s2.0-S1074761314002283-main.pdf?_tid=859ead72-65ca-11e4-b0c8-00000aacb361&acdnat=1415288302_6dba44d332f5ccae4674c04d93b6f6c5

http://www.ncbi.nlm.nih.gov/pubmed/21670203?dopt=Abstract

http://jem.rupress.org/content/208/12/2561.long

http://www.ncbi.nlm.nih.gov/pubmed/9653099

http://www.ncbi.nlm.nih.gov/pubmed/23908469

http://www.ncbi.nlm.nih.gov/pubmed/23964115