When the human body is defending and removing foreign bodies such as invading pathogens, it has a function to make white blood cells converge. Some substances that can cause this function are called chemokine. Chemokine is a kind of small molecule protein which plays an important role in the physiological function of human body. It is mainly secreted by immune cells and glial cells and has chemotactic activity. Some chemokines can promote inflammation, while others are thought to control cell migration during normal repair or development. These proteins bind to chemokine receptors (g-protein-coupled transmembrane receptors) and are selectively expressed on the surface of target cells. These proteins are selectively expressed on the surface of target cells by binding to chemokine receptors (g-protein-coupled transmembrane receptors). Chemokines are found in all vertebrates, some viruses and some bacteria, but not in other invertebrates.

The main function of chemokine is to facilitate the migration of cells. Some chemokines control chemotaxis of immune cells during immune surveillance, such as inducing lymphocytes to lymph nodes. Chemokines in these lymph nodes, called homeostatic chemokines, can be produced without stimulation, and are secreted to monitor pathogen invasion by interacting with antigen-presenting cells in these tissues. The release of chemokines can also stimulate the release of inflammatory cytokines such as interleukin 1 (IL-1). The main role of inflammatory chemokines is to move chemotactic leukocytes (such as monocytes and neutrophils) from the bloodstream to the site of infection or tissue damage. Some chemokines can also promote wound healing. Here we introduce several typical chemokines below:

1.CCL2

As one of the members of the CC subfamily of chemotactic factors, CCL2 is one of the most widely studied chemotactic factors, namely mono-cyte chemotactic protein-1 (MCP-1), which plays an important role in tissue damage and repair of many inflammatory diseases. It can chemotactic monocytes, macrophages and T lymphocytes, affect their phagocytosis and produce antibodies, so as to fight against the physiological function of foreign invading microorganisms. As CCL2 plays a wide role and is expressed in various parts of the body, studies in recent years have found that CCL2 plays a key role in the occurrence and development of tumors, central nervous system diseases, immune system diseases, AIDS, leukemia, diabetes and other diseases.

2.CXCL10

CXC chemokine ligand-10 (CXCL10) is an important chemokine recently discovered and belongs to the non-ELR subgroup of CXC. CXCL10 mainly mediates Th type inflammatory reaction, chemotactic T lymphocytes and monocytes, and is related to inflammatory diseases, autoimmune diseases and tumors. Recent studies have found that the increased expression of CXCL10 in different types of liver diseases may be closely related to the occurrence, development, treatment and prognosis of the disease.

3.CXCL12

CXCL12 has a strong chemotactic effect on lymphocytes and plays an important role in their development. During embryonic development, CXCL12 directs the migration of hematopoietic stem cells from the fetal liver to the bone marrow. Mice with CXCL12 knockout often died in the womb or within an hour of birth. SDF-1α/CXCL12a can also affect the electrophysiology of neurons. CXCL12 can be expressed in many tissues (including brain, thymus, heart, lung, liver, kidney, bone marrow, spleen). The receptor for CXCL12 is CXCR4.However, it has recently been suggested that CXCL12 can also bind to the CXCR7 receptor.

4.CXCL16

CXC chemokine ligand-16(CXCL16) is a new chemokine produced by defensive immune cells at the invasion site, which has a variety of biological functions. Recently, it has been found that it is also expressed in inflammatory tumors and has attracted people's attention. It is involved in the chemotaxis of inflammatory cells to pathological tissues through CXCR6, affecting the proliferation of tumor cells or inducing tumor angiogenesis. Recently, it was found that CXCL16 expression can be detected in tissue samples and cell lines of various lymphomas (including B cell, T cell lymphoma as well as HL), and the expression of CXCL16 in H/RS cells of Hodgkin's lymphoma is negatively correlated with the expression of CD99. More and more studies have shown that CXCL16 is involved in tumor formation, cancer progression, metastasis, cell proliferation and migration.

Chemokines and their receptors have a wide range of cellular sources and biological effects and play an important role in the occurrence and development of a variety of diseases. Chemokine networks in human tumors are complex and their effects are only partially reported. There is still a great deal of unknown information to be studied. With the in-depth research on cytokines and their receptors, it may open up new ways for the treatment of some human diseases, such as atherosclerosis, autoimmune diseases, organ transplantation, HIV infection and tumors, and would open up new prospects for the clinical treatment.