Effects of magnetic fields on immune system, tissue repair and fibrosis

Abstract

Tissue repair and regeneration are vital biological processes that involve three intertwined stages of inflammation, proliferation, and remodeling. The immune system plays an important role in each stage to regulate the processes of tissue repair, mainly by a complex network consisting of immune cells and the secreted cytokines. In recent years, with the popularity of electronic devices and magnetic materials, the biological effects of magnetic fields (MFs) have received widespread attention, and research on the effects of MFs on biological tissue repair and fibrosis has made a series of advantages. Using different types of MFs of varying strengths, researchers have found that MFs modulate the body’s immune system in various disease models. MFs affect the process of tissue repair and scarring by changing the number, function and phenotype of immune cells. Macrophages have two distinct functions in the processes of wound healing and these functions are closely related to their phenotypic changes in different physiological states. Inflammatory macrophages (M1 type) disrupt the normal metabolism of cells, induce apoptosis, or exacerbate ischemia and hypoxia. Anti-inflammatory macrophages (M2 type) bridge the processes of tissue repair by activating and supporting the function of stem cells/progenitor cells, and remodeling extracellular matrix components to provide scaffold for tissue regeneration and angiogenesis. MFs thus change the phenotype and function of macrophages through various mechanisms, thereby regulate the repair processes of damage. Mesenchymal stem cells (MSCs) are a group of multifunctional cells that have the ability to differentiate into bone cells, adipocytes, and chondrocytes. They are recruited to the site of injury and can interact directly with other immune cells, thus inhibit inflammation and promote tissue repair. Some studies suggest that MFs could not only improve the differentiation potential of MSCs, but also promote MSCs accumulation in the target tissue. Myeloid-derived suppressor cells (MDSCs) are a group of cells with immunosuppressive functions. The phenotype and number of MDSCs can be changed by MFs, therefore MFs may exert the function of regulating tissue repair via changing the state of MDSCs, thus, participating in pathological processes such as immune regulation and inflammatory response of tumorigenesis. Researchers also reported that MFs influence tissue repair though neutrophils and keratinocyte, and enhance the therapy efficacy of antibiotics. Fibrotic scar is a structure formed by excessive extracellular matrix deposition during tissue repairing process, and differs from normal tissue morphology. As the function of macrophages, MSCs and fibroblasts can be affected by MFs, MFs have the ability to regulate fibrosis formation. This review article focuses on the effect of MFs on tissue repairing and regeneration. Further exploration of the role of MFs in tissue repairing and fibrosis formation will lead to new ideas for using MFs in disease treating.