Lymphocytes are smaller than phagocytes and their nucleus fills most of the cell. They are produced before birth in the bone marrow.
- Remain in the bone marrow until they are mature.
- Spread through the body but concentrate in lymph nodes, spleen and liver.
- Are specific to one antigen (only make one type of antibody molecule).
- Circulate between blood and lymph.
- Divide in bone marrow (mitosis) to form clones with the same genetic code for the same antibody. Part of each antibody forms antibody receptors - found in plasma membrane.
- During infection, only cells with the right antibody receptor which fits invading antigen divide rapidly.
There are 2 main types of B lymphocytes: plasma cells and memory cells.
- Plasma cells produce antibodies which are released into the blood, lymph, linings of lungs and gut. They are released at several 1000 per second.
- Memory cells remain in circulation for a long time. If there is a second infection, they divide rapidly and produce more plasma and memory cells.
The primary response is slow as few B cells are specific to the antigen. The secondary response is faster as there are many memory cells which divide rapidly and make plasma cells. Secondary response is not only faster but more antibodies are produced. Memory cells are the basis of immunological memory.