Specific Immune Response: B Lymphocytes
Maturation of B-lymphocytes
- B-lymphocytes (B cells) remain in the bone marrow until they are mature and then spread through the body, concentrating in lymph nodes and the spleen
- During the process of maturation B cells gain specific cell surface receptors called B cell receptors (BCRs)
- The receptors on the cell surface of B cells are antibodies and are sometimes referred to as antibody receptors
- Part of each antibody molecule forms a glycoprotein receptor that can combine specifically with one type of antigen
- A small number of B cells have the same BCRs, these genetically identical cells are called a clone
Mature B cells have many different types of antibody receptor on their cell surface membranes
B cells in the immune response
- In order to play their role in the immune response B cells need to be activated and increase in number; this occurs as follows:
- Clonal selection and activation
- B cells with complementary antibody receptors bind to antigens on antigen presenting cells; this is clonal selection
- These antigen presenting cells can be phagocytes, infected cells, or the pathogens themselves
- This binding, together with interleukins released by T helper cells activates the B cells
- B cells with complementary antibody receptors bind to antigens on antigen presenting cells; this is clonal selection
- Clonal expansion
- Activated B cells divide by mitosis to produce clones
- This results in large numbers of identical B-lymphocytes being produced over a few weeks
- Some of these B-lymphocytes differentiate into plasma cells
- Plasma cells secrete lots of antibody molecules (specific to the antigen) into the blood, lymph or linings of the lungs and the gut
- The other B-lymphocytes become memory cells that remain circulating in the blood for a long time
Activated B cells differentiate into plasma cells and memory cells
