Eotaxin refers to a subfamily of proteins that are categorized as being eosinophil chemotactic. There are three members of the eotaxin family in humans; eotaxin-1, eotaxin-2, and eotaxin-3. This family is defined as a CC Chemokine family because two of its cysteines are next to their amino terminus.
Eotaxin-1 is encoded by the CC11 gene, and you will find it on chromosome 17. Eotaxin-2 is encoded by the CCL24 gene and will be found on chromosome 7. Finally, eotaxin-3 is encoded by the CCL26 gene and is also found on chromosome 4 in humans.
The structural makeup of eotaxin is easily characterized thanks to its four cysteines. As already mentioned, two of these are found adjacent to the amino terminus. The eotaxin found in humans is said to be an 8.4kDA, 74 aa residue polypeptide.
Mechanism & Interactions
All three members of the eotaxin family are produced by numerous cells throughout the human body. Eotaxin-1 is known for carefully recruiting eosinophils (these are a type of white blood cells) by forcing them to move. It binds to a chemokine receptor - which is a G-protein-linked receptor. This member of the eotaxin family is said to be particularly selective about which chemokine receptors it binds to. Technically speaking, it has the ability to bind to CCR2, CCR3 and CCR5. Nevertheless, it mainly only binds to CCR3. There have been many instances where eotaxin-1 refuses to bind with certain types of white blood cell that does not exhibit the chemokine receptor CCR3.
Eotaxin-2 also interacts with the chemokine receptor CCR3. This is the only receptor it interacts with, but it also helps produce the chemotaxis effect in eosinophils. Furthermore, unlike eotaxin-1, this eotaxin is known to induce major chemotaxis in T lymphocytes, and even a slight bit in neutrophils.
Eotaxin-3 completes the group of eotaxins that has an affinity to bind with chemokine receptor CCR3. It is produced throughout the body by several tissues in major organs such as the heart, ovary, and lung. Furthermore, many endothelial cells express eotaxin-3 if they have been properly stimulated. Eotaxin-3 is considered to be extremely chemotactic for both basophils and eosinophils - this means it induces chemotaxis in both.
The primary function of eotaxin is to work with eosinophils. It can help induce chemotaxis in these white blood cells, which essentially means it gets them to move towards certain areas of the body. In essence, this helps deal with inflammation by swarming the inflamed area with white blood cells to help fight it off. Eotaxins normally function in relation to allergic responses, but there have been various studies involving test subjects with high eotaxin levels.
Most notably, it’s found that patients with asthma tend to have abnormally elevated levels of eotaxin-2 in their blood. It’s considered this is due to the fact that patients with asthma will usually have an allergic reaction to something or suffer from inflammation of some kind. Therefore, the eotaxin family kicks into action in an attempt to recruit eosinophils by forcing chemotaxis in these cells.