When a B cell encounters its triggering antigen, it gives rise to many large cells known as plasma cells. Every plasma cell is essentially a factory for producing antibody. Each of the plasma cells descended from a given B cell manufactures millions of identical antibody molecules and pours them into the bloodstream. An antibody matches an antigen much as a key matches a lock. But whenever antibody and antigen interlock, the antibody marks the antigen for destruction.
Different types play different roles in the immune defense strategy.
Immunoglobulin G, or IgG, works efficiently to coat microbes, speeding their uptake by other cells in the immune system. Immunoglobulin M is very effective in killing bacteria. Immunoglobulin E, whose natural job probably is to protect against parasite infections, is the villain responsible for the symptoms of allergy. T cells contribute to the immune defenses in two major ways. Some direct and regulate the immune responses.