Macrophages in the skin: role in physiological processes and in response to cosmetic procedures. A review

Macrophages are a heterogeneous population of immune cells derived primarily from bone marrow monocytes and embryonic yolk sac erythromyeloid progenitors, capable of altering their phenotype and functions depending on the microenvironment. This article presents a review of current knowledge on the origin, structure, and function of dermal macrophages, including historical data from the first observations by I.A.E. Goeze (1777), confirmed by W.F. von Gleichen-Russwurm, the term "Fresszellen" by K. Klaus, and the phagocytic theory of I.I. Mechnikov (1882–1884) to the M1/M2 dichotomy of Mills et al. (early 2000s). This paper summarizes literature data on the human monocyte-macrophage system in both normal and pathological conditions, taking into account the heterogeneity of classical monocytes as precursors of tissue macrophages, non-classical monocytes for endothelial homeostasis, intermediate and organ-specific macrophages (Langerhans cells in the epidermis, microglia in the central nervous system, and Kupffer cells in the liver). Data are presented on various macrophage phenotypes, from proinflammatory M1 with glycolytic metabolism and inducible nitric oxide synthase to reparative M2 with mitochondrial respiration and arginase-1, and their involvement in immune surveillance, skin protection, regeneration, angiogenesis, and tissue remodeling. The article presents an analysis of the role of macrophages in response to cosmetic procedures: ablative and non-ablative lasers 10600 and 1550 nm, microneedle RF, SMAS-lifting, injections of polylactic acid, calcium hydroxyapatite, the role of Langerhans cells in response to external stimuli of ultraviolet radiation, cosmetics, etc., the role of macrophages in the development of fibrosis M₁-initiation, M_2a-proliferation, M_2c-resolution, SPP1+ with CXCL4 from platelets, PRP-hypothesis, regulation of the adipocyte population in dermal-associated adipose tissue dWAT, elimination of biomaterials. Attention is paid to resident dermal macrophages located perivascularly and perineurally in the papillary and reticular layers, their ability to proliferate in situ to maintain homeostasis, the synthesis of collagenase enzymes, elastase, hyaluronidase and cytokines that regulate the functions of dermal and epidermal cells.