Antibody Production and Memory Cells
When an infection begins, some of the B cells circulating throughout the body will recognize and present antigens which are produced by the invading pathogen. B cells which present antigens on their surfaces will then receive an activating signal from a helper T cell, along with cytokines secreted by type 2 helper cells. When this happens, those B cells become activated, and will divide continuously for four or five days. After this point, one of several things may happen.
Depending on the specific type of pathogen involved, the B cells may receive chemical signals from other immune cells and molecules, which cause the cells to respond in certain ways. Depending on the chemical instructions received, the B cell might become an antibody-producing plasma cell, or become a memory cell. It may also undergo a process called isotype switching, in which it becomes programmed to produce a particular class of antibody.
Plasma B cells are more or less antibody factories, doing little else but producing and secreting huge amounts of antibody. There are five different types of antibody: the kind produced by B cells typically depends on the specific type of pathogen which has invaded the body (the next part of this series will focus on these different types of antibodies, and their specific functions and effects).
Memory cells, on the other hand, do not produce antibody during an initial infection. Instead, they remain in the body for years—possibly an entire lifetime—dividing and persisting, ready to be activated if the same type of pathogen causes a subsequent infection.