Lymphocytes are a group of white blood cells (leukocytes) that are produced in the bone marrow. They are present in the blood, lymph, connective tissue and lymphoid organs such as lymph nodes, spleen, tonsils, adenoids and Peyer’s patches. The lymphocytes play a major role in immune responses: humoral immunity response, associated with the production of antibodies; and cellular immunity, associated with proliferation of effector cells – a specific group of cells in the immune system that response to stimulus.
In healthy people, there are 4,500-10,000 white blood cells per microliter (mcL). The number varies depending on age and certain medications. For instance, the number increases in case of infections or inflammation. However, despite the increase of blood cells in a healthy person, lymphocytes represent 20 to 40% of white blood cells. Normally, the number of lymphocytes permilliliter (ml) must be:
- less than 4000 in adults
- less than 7 000 in children
- less than 9 000 in an infant.
All these white cells go through a predictable life cycle – they naturally die (when they become too old) to be replaced by new ones. In the case of Non-Hodgkin’s lymphoma, white blood cells can multiply excessively and, without going through this natural death; this condition causes formation of cancer cells.