Fig. 5.

Sources of MSCs and the Pathways of MSCs exerting immunomodulatory effects. a MSCs can be isolated from the bone marrow, adipose tissue, dental pulp, umbilical cord and placenta, peripheral blood, and induced pluripotent stem cells. b There are three main pathways for MSCs to exert immunomodulatory effects: ① Paracrine effects, including microvesicles, exosomes and bioactive molecules; ② Cell-to-cell contact, including direct intercellular contact and intercellular contact mediated by the binding of cell surface receptors and ligands; ③ Apoptotic MSCs: MSCs are attacked by complement system components, complement activated neutrophils and perforin positive cytotoxic cells, then phagocytes engulf apoptotic MSCs to mediate immune regulation