Macrophages in the embryo and beyond: Much more than just giant phagocytes

Abstract

Originally recognized as an essential part of the innate and acquired immune systems, macrophages emerged as omnipresent and influential regulators of embryo- and organo-genesis, as well as of tissue and tumor growth. Macrophages are present essentially in all tissues, beginning with embryonic development and, in addition to their role in host defense and in the clearance of apoptotic cells, are being increasingly recognized for their trophic function and role in regeneration. Some tissue macrophages are also found to possess a substantial potential for autonomous self-renewal. Macrophages are associated with a significant proportion of malignant tumors and are widely recognized for their angiogenesis-promoting and trophic roles, making them one of the new promising targets for cancer therapies. Recent expression profiling of embryonic macrophages from different tissues revealed remarkable consistency of their gene expression profiles, independent of their tissue of origin, as well as their similarities with tumor-associated macrophages. Macrophages are also capable of fusion with other cells in tissue repair and metastasizing tumors, as well as with each other in the immune response and osteoclastogenesis.

Circulating giant macrophages as a potential biomarker of solid tumors

“…In turn TAMs secrete cytokines and growth factors (e.g., MMP-1, CXCL12) which stimulate tumor cells with the potential to become circulating tumor cells (CTCs) (2)(3)(4). TAMs and CTCs then migrate via the lymphatic system or intravasate across intratumor capillary barriers into peripheral circulation (4)(5)(6)(7)(8)(9).…”

Colony-Stimulating Factor-1 Promotes Kidney Growth and Repair via Alteration of Macrophage Responses

“…Although their role in host defense has been well documented, macrophages and their precursors are also important during embryogenesis, normal tissue maintenance, and postnatal organ repair. 1,2 Almost all developing organs contain a population of resident monocytes that infiltrate very early during organogenesis and persist throughout adult life. [3][4][5][6] In addition to their phagocytic capabilities during tissue remodeling-associated apoptosis, 5,7 fetal macrophages have many trophic effects that promote tissue and organ growth.…”

“…3 Embryonic macrophages appear to play a positive trophic role that may have parallel reparative functions in many adult tissues undergoing repair and cellular replacement. 1,20 A number of studies have suggested that infiltrating macrophages along with the trophic factors they release participate in tissue repair of the kidney, 20 -22 brain, 23 skin, 24,25 lung, 26 liver, 27 heart, 28 gastrointestinal tract, 29,30 and skeletal muscle. 31,32 Indeed, the pleiotrophic roles for CSF-1 in reproduction, development of multiple organ systems, and maternal-fetal interactions during pregnancy by macrophage-mediated processes have also been well defined.…”

Building towards a standardised approach to biocorrosion studies: a review of factors influencing Mg corrosion in vitro pertinent to in vivo corrosion

“…Macrophages are a type of white blood cell that are commonly associated with these reactions [93,94]. Macrophages are found in all tissues [95], and are known to secrete reactive oxygen species (ROS) which have been found to increase the corrosion of other metallic biomaterials such as Ti [96].…”