IMMUNOBIOLOGY 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 reper-toire and mechanisms underlying func-tional 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 indepen-dent 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 docu-mented as associated with M2. Overall, the common signature genes provide a molecular basis for a number of docu-mented or suggested properties of M2, including immunomodulation, down-regulation of inflammation, protection against oxidative damage, high capacity for phagocytosis, and tissue repair. Inter-estingly, several common M2 signature genes encode membrane-associated markers that could be useful for the iden-tification and isolation of M2. Some of these genes were not induced by IL-4/ IL-13 or IL-10 under various in vitro set-tings and thus were missed in approaches based on in vitro–activated cells, validat-ing our choice of in vivo models for expression profiling of myeloid cells