However, this means there are only a very few cells floating around or blood system that are able to recognize any one specific antigen. Clearly we need a lot of immune cells to fight off an infection so there needs to be some form of mechanism that will promote the proliferation of just those cells that are capable of responding to a particular infection as and when it occurs. Although they didn't know it, this is what enabled Edward Jenner and Louis Pasteur to develop vaccines. The ability of the adaptive immune system to learn what is dangerous permits its education through vaccination techniques. The adaptive immune system is able to learn from its successes and mistakes unlike the innate immune system.
Innate system is the first line of defense.
The holding barrier while the adaptive forces muster and organize them selves ready for the counter offensive against the pathogenic challenge. The adaptive immune system is comprised of lymphocytes. The lymphocyte population is grouped into two types, T lymphocytes and B cells. At any one time we have around 1,000,000,000,000 lymphocytes either circulating or deposited in our lymphoid organs. There is a high turnover rate of production with 1,000,000,000 new lymphocyte cells being produced every day.