The protein, which scientists call Lck, is essential for immune system T cells – white blood cells that attack virus-infected cells, foreign cells and cancer cells… Lck is important in helping “naive” T cells – those cells that have never been exposed to a particular pathogen – capture the receptor template of the invading agent and store it for future reference… Following infection or vaccination, Lck initiates a biochemical chain of events that vastly increases the number of T cells that march off to combat the invader.

After the infection subsides, the number of T cells marshaled to fight that agent decreases dramatically. But a smaller subset, known as “memory” cells, retains the imprint of its previous encounter should the pathogen make a return appearance. According to the study, while Lck primes naive cells to fight a pathogen, it is not required by memory cells, which initiate the fast and furious response when that same pathogen comes calling again years later. Unlike naive T cells, which are confined to the lymphatic system, memory T cells are found everywhere in the body, enabling them to sense and react more quickly when an infectious agent is reencountered.