Our immune system depends on interleukin 21 (IL-21), according to a team of scientists. They discovered that this molecule acts as a growth factor for a subset of T cells called T follicular helper (TFH) cells. The researchers say that without IL-21, the TFH cells could neither develop nor survive.
“Without IL-21, we probably wouldn't be completely immunodeficient, just severely compromised,” explains Cecile King, Ph.D., head of the mucosal autoimmunity group at the Garvan Institute of Medical Research in Sydney.
TFH cells have been identified to play a critical role in that they communicate with and help activate B cells. These TFH cells act in specialized areas within lymph organs, called germinal centers, where B cells proliferate to form antibodies.
“We showed that if you take a mouse genetically deficient in IL-21 and immunize it, you don't get TFH cells, and you don't get antibody production,” reports Dr. King. “Conversely, if you put IL-21 receptor sufficient, or normal, T cells into the same mouse, where of course the B cells remain abnormal, you recover the normal immune reaction.”
A paper detailing this finding is published in Immunity.