Chemokine (C-X3-C motif) ligand 1 (CX3CL1, also known as fractalkine) and its receptor chemokine (C-X3-C motif) receptor 1 (CX3CR1) are widely expressed in immune cells and non-immune cells throughout organisms. However, their expression is mostly cell type-specific in each tissue. CX3CR1 expression can be found in monocytes, macrophages, dendritic cells, T cells, and natural killer (NK) cells. Interaction between CX3CL1 and CX3CR1 can mediate chemotaxis of immune cells according to concentration gradient of ligands. CX3CR1 expressing immune cells have a main role in either pro-inflammatory or anti-inflammatory response depending on environmental condition. In a given tissue such as bone marrow, brain, lung, liver, gut, and cancer, CX3CR1 expressing cells can maintain tissue homeostasis. Under pathologic conditions, however, CX3CR1 expressing cells can play a critical role in disease pathogenesis. Here, we discuss recent progresses of CX3CL1/CX3CR1 in major tissues and their relationships with human diseases.
This work was supported by the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT and future Planning (NRF-2017R1A2B4002419) and a grant from the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health and Welfare, Republic of Korea (grant number HI15C1980).