The first group of signals is generated in conditions such as infection, cancer, and inflammatory environments and includes granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), granulocyte colony-stimulating factor (G-CSF), vascular endothelial growth factor (VEGF), and prostaglandin E2 (PGE2) [5, 29, 30]. Here, CSF2 is linked to infection.