The J Chain Enigma: Evolutionary Origin of Mysterious Immune System Molecule

The human immune system appears to have evolutionarily co-opted a molecule from another biological process.
Researchers discovered that a protein called the J chain, which helps the immune system function properly, originally came from a different family of genes known as CXCL chemokines. Published in the Proceedings of the National Academy of Sciences, their findings help us better understand how the immune system works and could lead to new ways to treat diseases.

Evolution and Adaptation in Immune Proteins
In several ways, biological systems can behave as siblings, including by borrowing something and never giving it back. That appears to be what the human immune system did with a protein that now helps bind and regulate the subunits that make up antibodies, according to a multi-institute research collaboration. They found that, before the immune system evolutionarily co-opted it, the protein originally belonged to the gene family responsible for directing cells to move to the right location at the right time to address specific functional needs.