Fig. 4
Genesis, diversity, and features of Tumor-Associated Macrophages during tumor progression and growth. Tissue-resident macrophages are derived from embryonic progenitors or HSC-derived circulating monocytes for the steady-state duration. In addition, numerous monocyte subpopulations assist in intruding myelogenous cells such as TIM, TEM, and TAM into the tumor (200). During tumor progression, TAMs may instigate through embryonic/monocytic tissue-resident macrophages activated or phenotypically altered in the course of carcinogenesis (tissue-resident TAMs) or response to tumor growth (tumor-induced TAMs). Monocytes can also directly infiltrate tumor tissue as tumor-induced effector monocyte. TAMs recruit macrophages by inducing various transcriptome and cell surface markers from a subpopulation of macrophages and embracing different pro-tumoral functions based on the TME. Such activities cause tumor initiation by inflammation, tumor progression to malignancy by stimulating angiogenesis, immunosuppression, invasion, intravasation, tumor cell extravasation at remote sites, and obstinate development of tumors. TAM tumor-associated macrophage, TEM Tie-2 [angiopoietin-2 (Ang-2)] expressing monocyte, TIM tumor-infiltrating monocyte, VEGF-A vascular endothelial growth factor A, EMAPII endothelial-monocyte-activating polypeptide II, Sema3A Semaphorin-3A. Treg regulatory T cell, DC dendritic cell
