CCL21 is often referred to as Exodus-2 and is considered to be a minor cytokine of the CC chemokine family. All cytokines are small proteins that play a significant role in the signalling of various cells. When they’re released into the bloodstream, it has an immediate and noticeable effect on how the cells around them behave.
The CC chemokine family - which CCL21 is a member of - is known for having the power to directly induce chemotaxis in cells that are close by. As well as being referred to as Exodus-2 by some people, CCL21 has also been called 6Ckine by many scientists and researchers.
Typically, all chemokines follow a similar structural makeup. They’re noticeable for having four cysteines. However, CCL21 doesn’t follow this trend as it has six cysteines instead of the normal four. This is what led to it being referred to as 6Ckine. Having said that, it does follow the typical structural feature of other cytokines in the CC chemokine family by having two adjacent cysteines.
It is considered to be an antimicrobial gene and is one of many that are located on chromosome 9. More specifically, CCL21 can be found on the p-arm of this chromosome.
Mechanism & Interactions
CCL21 is known for having a very high affinity for chemokine receptor 7 (CCR7). It binds to this receptor in order to give off its desired effects. The main producers of CCL21 are endothelial cells (the cells that line the inside surface of blood vessels) which are present all over the body. Primarily, endothelial cells in the lymph nodes, appendix and spleen, will produce the most CCL21.
When secreted by these cells, CCL21 binds to CCR7 and will then attract T cells and other mature dendritic cells. A T Cell is a particular type of white blood cell that is mainly present in immunity within cells. They mainly help with the natural immune function of the body. Dendritic cells are found all throughout the body and are described as antigen-presenting cells. They help provide antigen material to the surface of T-Cells. So, when CCL21 is secreted, it helps bring both of these things together.
Therefore, the main function of CCL21 is to attract both dendritic and T cells to a particular part of the body. Here, these two cells can work together to help with cell maintained immunity. The dendritic cells flood the scene where they find plenty of T Cells that were brought there by the CCL21 chemokine. From here, the dendritic cells produce even more CCL21 (along with CCL19) which helps call more mature dendritic cells to the area. There has also been research that suggests a secondary function of CCL21 is to slow down and prevent the process of hematopoiesis.
CCL21 has been used in various studies, many of which relate to tumours. It has been found that some test subjects that were given an injection of CCL21 - to help produce more of it than normal - saw a decrease in their tumour growth. The overexpression of CCL21 also helped to flood the tumour with more T cells and dendritic cells.