One of the main types of cells involved in the humoral immune response is the B cell. These lymphocytes, or white blood cells, are designed to provide immunity in the body by developing antibodies when they are exposed to antigens, or foreign bodies that invoke an immune response. B cells are produced in the bone marrow, which provides a steady supply of them to the body. They later mature into one of two types of cells: plasma B cells and memory B cells.
As they are generated continuously, millions of B cells are made in the human body each day, making them the most common type of lymphocyte. These immature cells are activated when they come into contact with an antigen, which forces them to mature, and then released into the bloodstream and lymphatic system. A mature B cell is then capable of creating antibodies specific to that antigen. This adaptive nature of B cells makes them a critical part of the immune system's ability to fight off infection.
An immature B cell can mature in one of two ways. Some become plasma B cells, which produce large amounts of antibodies to fight the antigen that first triggered their development. These cells tend to be relatively short-lived, responding strongly to fight a particular infection but then dying off once it is gone. Memory B cells, on the other hand, remain in the body for a longer period. They are also formed when an antigen first invades the body, but they continue to travel in the bloodstream and will respond to the antigen if it enters the body a second time.
B cells that develop from other, mature cells are clones of the original. This means that they will respond to the same antigen that the original cell does. This is important for a healthy immune response to an invading disease, as the original B cell can divide many times and all of the resulting lymphocytes will be capable of attacking the infection. The ability to clone is true for both plasma cells and memory cells.
Sometimes a B cell may mutate and become cancerous. This can lead to a type of cancer known as a lymphoma. Like normal B cells, the cancerous cells will clone themselves, which then leads to the spread of cancer through the body as the mutated lymphocytes proliferate in the bloodstream.