Identification of a common gene signature for type II cytokine-associated myeloid cells elicited in vivo in different pathologic conditions.

Compared with type I cytokine-associated myeloid (M1) cells, the molecular repertoire and mechanisms underlying functional properties of type II cytokine-associated myeloid (M2) cells are poorly characterized. Moreover, most studies have been limited to in vitro-elicited M2 cells. Here, comparative gene expression profiling of M1 and M2 cells, elicited in murine models of parasitic infections and cancer, yielded a common signature for in vivo-induced M2 populations independent of disease model, mouse strain, and organ source of cells. Some of these genes, such as cadherin-1, selenoprotein P, platelet-activating factor acetylhydrolase, and prosaposin, had not been documented as associated with M2. Overall, the common signature genes provide a molecular basis for a number of documented or suggested properties of M2, including immunomodulation, down-regulation of inflammation, protection against oxidative damage, high capacity for phagocytosis, and tissue repair. Interestingly, several common M2 signature genes encode membrane-associated markers that could be useful for the identification and isolation of M2. Some of these genes were not induced by IL-4/IL-13 or IL-10 under various in vitro settings and thus were missed in approaches based on in vitro-activated cells, validating our choice of in vivo models for expression profiling of myeloid cells.