Figure 7. Schematic illustration of the spiral effects of the CCL2–CCR2 and CCL22–CCR4 axes through interactions between tumor-associated macrophages (TAMs) and prostate cancer cells.

Infiltrated macrophages become M2-type cells (TAMs) through stimulation with prostate cancer cells. The interactions between TAMs and prostate cancer cells induce CCL2 in prostate cancer cells and affect the TAMs and prostate cancer cells in an autocrine manner. CCL2 upregulates its receptor, and through acceleration of the CCL2–CCR2 signal, CCL22 and CCR4 are upregulated. Subsequently, the CCL22–CCR4 axis activates Akt, which results in prostate cancer migration and invasion.