Antibodies are not constantly being produced. Their production begins during an .
T-lymphocytes interact with a pathogen's antigen, typically in the blood. They mature into either killer cells, which begin to destroy the pathogen, or helper cells, which produce cytokines that signal to B-lymphocytes.
When they receive the signal, they mature into plasma cells and begin to produce antibodies. They are specific to the pathogen's antigen and can target and destroy it.