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. Author manuscript; available in PMC: 2009 Jun 20.
Published in final edited form as: Curr Opin Genet Dev. 2008 Mar 4;18(1):11–18. doi: 10.1016/j.gde.2007.12.007

Figure 3.

Figure 3

Macrophages are differentially activated by different cytokines or other factors and become either tumor-promoting or tumoricidal. Classically-activated or M1 macrophages produce high levels of type 1 cytokines that promote a tumor-rejecting type 1 response as well as factors such as inducible nitric oxide synthase which are cytotoxic for tumor cells, and low levels of type 2 cytokines. In contrast, alternatively-activated or M2 macrophages produce high levels of cytokines that polarize immunity towards a tumor-promoting type 2 response, and low levels of cytokines that promote a tumor-destructive type 1 response. Some of the molecules produced by M2 macrophages attract additional pro-inflammatory mediators to the tumor site, thereby amplifying the inflammatory microenvironment.