T and B lymphocyte life cycle – effector and memory lymphocytes
In the video on the naïve lymphocyte page, did you hear the activated T cells being referred to as "effector cells" and did you wonder what was meant by that?
Both activated B and T cells develop into either effector cells that actively carry out specific functions or into memory cells. When B cells become activated, they first develop into either plasmablasts or memory B cells. The plasmablasts migrate to the bone marrow where they mature into effector cells called plasma cells and these cells are the antibody producing factories. Effector-helper T cells are the T cells that express the co-receptor CD4 and they help cells live by secreting bucket loads of cytokines, whereas effector killer T cells, which are the CD8 expressing T cells, are assassins ready to kill other cells. Both effector and memory T cells leave the secondary lymphoid organs and migrate to the tissue where the antigen was first picked up by the APCs. This makes sense, as this is the place where the effector function is needed to combat the pathogen that the antigen originated from!
Effector lymphocytes have a life span that ranges from a few days to a few weeks. Memory lymphocytes, however, have a long lifespan providing us with lifelong immunity to infectious agents, which is referred to as immunological memory. These memory lymphocytes tuck away in the tissue where they lie in wait, ready to pounce on the same pathogen should it return. The resulting secondary immune response is therefore faster than the primary immune response because the memory lymphocytes are already in place. The secondary immune response is also stronger because there are a higher number of antigen specific lymphocytes available following the clonal expansion that took place during the primary immune response. Memory lymphocytes are also easier to activate than naive lymphocytes, so less antigen is needed to get the secondary immune response going. Immunological memory is therefore a great mechanism to quickly destroy some very nasty invaders before they kill you!