14 DAY TRIAL // The vertebrates have a sophisticated immune system, called adaptive immune system, which is capable of reacting and developing defenses against novel microbes and viruses. The genes responsible for this system are called Rag genes and it was previously thought that they have appeared in jawed vertebrates. Their appearance is known as the "big bang" of immunology and it is thought to have happened around 450 million years ago.
In fact, both types of vertebrates, jawed (like us) and unjawed (like the lampreys), have adaptive immune systems but they are significantly different. The Rag genes are responsible for our type of adaptive immune system.
More precisely, they create two enzymes, called Rag1 and Rag2, which cut apart and rearrange the DNA inside the body's immune cells. This produces a large variability among these immune cells (the T cells) and a large variability of antibodies which is necessary for putting together a quick response to a novel intruder (virus or microbe). The organism simply randomly generates a large bulk of different antibodies until some of them fit the intruders. The Rag genes are thus the ones that make possible this random generation of different antibodies and the adaptive immune system.
But researchers from the University of Toronto (UoT) and from the National Institute on Aging (NIA) in Baltimore have now discovered that the purple sea urchin, which is only a humble invertebrate, also has the Rag genes.
According to immunologist Sebastian Fugmann from NIA, the genes inside the sea urchin produce enzymes which are similar to the vertebrates' Rag1 and Rag2, but it is yet unknown what function they play inside the invertebrates.
Immunologist Jonathan Rast from UoT has said that this discovery "allows for a longer, multistep process for the [immune] system to evolve". Thus, there was no "big bang" of immunology but only a gradual evolution.
The evolutionary process at work here is in fact a very widespread process. It often happened that some feature was good for something and at certain point in time it was "snatched" by some other function. In this case the adaptive immune system has "snatched" the Rag1 and Rag2 enzymes from whatever use they might have had in invertebrates. Other more spectacular examples include how in case of the tetrapodes emerging out of the water the function of hearing "snatched" the ears from the function of breathing.
Photo Credit: Jonathan Rast