Becoming alert to a pathogen requires massing troops to eliminate a rapidly reproducing infection. Because a body can make a hundred million or more different antibodies, carrying inventory is infeasible. The only way to combat an infection is to reproduce the right antibody for lymphocytes quickly and massively.
This multiplication miracle is accomplished by clonal selection: lymphocytes that come into contact with an antigen are triggered to undergo successive waves of self-cloning. This is how the immune system solves the problem of allowing many different antibody-specific lymphocytes to cruise the body, yet effectively counter an invasion by massive response.
Infection counteraction usually takes several days to produce a large enough concentration of antibodies. At the same time, the bug is rapidly reproducing.
Let’s go back to the point that the body can remember a 100 million antibody patterns. The actionable implication is that a 2nd or subsequent attack by the same infectious agent produces a quicker response than initial exposure. That is why vaccines work. A 1st-time reaction may take several days to have an effect, but a subsequent adaptive reaction can happen in a very few days.
The immune system functions as a network of shared information, regulated by interactions between lymphocytes and their secreted molecules. The immune system is not only a breakneck munitions factory, it’s a voluminous library. This knowledge is acquired through the education of the lymphatic system during early development, reaching back to the fetal stage.