B cells are a type of white blood cell that play a crucial role in the body’s immune system. There are two main types of B cells: naïve B cells and memory B cells. Naïve B cells are created in the bone marrow and have never been exposed to an antigen, while memory B cells are created in response to an antigen and can remember it for a long time.
B cells are important for the development of immunity against infection. They produce antibodies, which are proteins that help fight infection. When a foreign antigen is encountered, B cells produce specific antibodies that bind to the antigen and help destroy it.
B cells can also play a role in autoimmunity. In autoimmune diseases, the body’s own immune system attacks its own tissues. There is evidence that B cells can contribute to the development of autoimmune diseases by producing antibodies that target the body’s own tissues.
B cells make up between 5 and 15% of the lymphocytes that are found in the blood; they are also found in the bone marrow, the spleen, the lymph nodes, and the mucosa-associated lymphoid tissues.
B cells can present antigen to T cells and release cytokines, but their primary function is to develop into plasma cells, which manufacture and secrete antibodies.
The primary purpose of B cells is to grow into plasma cells, which are responsible for the production and secretion of antibodies. B cells can also release cytokines and present antigen to T cells.
The two stages of B cell response to antigen
Primary immune response:
When mature, naive B cells are exposed to antigen for the first time, they transform into lymphoblasts, go through clonal proliferation, and differentiate into memory cells. These memory record the instructions which enable the cell to react to the same antigen in the future, or develop into mature plasma cells that secrete antibodies.
This is known as the primary immune response.
There are several days of inactivity after an initial exposure to an antigen before the production of antibodies begins. After this point, only IgM will be generated.
Following this, with the assistance of T cells, B cells are able to perform additional rearrangement of their Ig genes and can then flip to the production of IgG, IgA, or IgE.
Because of this, the immune response following the first exposure is sluggish and initially only provides minimal protection.
The secondary immune response, also known as the anamnestic or booster reaction, occurs when memory B and Th cells are reexposed to the antigen. At this point, the memory B cells rapidly expand in number, develop into mature plasma cells, and release huge quantities of antibody (chiefly IgG because of a T cell–induced isotype switch). After being secreted into the blood and other tissues, the antibody is now in a position to interact with the offending antigen. Therefore, the immune response is both quicker and more effective after being reexposed to the pathogen.