Figure 3.

Effects of ERK activation in tumor infiltrating cells. ERK induces the proliferation of anti-tumor immune cells, such as CD8⁺ T-lymphocytes, immune-suppressive cells, such as myeloid derived suppressor cells (MDSC) and T-regulatory (Treg) cells, and cells that have either pro-tumor or anti-tumor activities, such as T-helper 17 (Th17) cells. Th17 cells can promote the pro-inflammatory phenotype of CD8⁺T-lymphocytes, differentiate into cells with a Treg phenotype, and expand MDSCs that induce apoptosis of CD8⁺ T-cells. Depending on the type of immune-population characterized by high ERK activity, a wide range of effects (ranging from an anti-tumor to a tumor tolerant/immune-suppressive environment) is obtained. Dashed arrows indicate a direct activation by Th17 cells; the dotted arrow indicates the product of a differentiation of Th17 cells.