Lymphocytes are a type of white blood cell and make up between 20 to 40 percent of the total white blood cell count. They play several roles in the immune system, including protection against bacteria, viruses, fungi, and parasites. Lymphocytes occur in three forms: B cells, T cells, and Natural Killer Cells. All three types can be increased in response to infections or cancer but in some cases only a specific type of lymphocyte is increased
Lymphocytes play an important function in the immune system. Too few B cells can lead to a decrease in the number of plasma cells, which produce antibodies. Decreased antibody production can cause an increase in bacterial infections. People who have too few T cells or too few NK cells have problems controlling certain infections, especially viral, fungal, and parasitic infections. Severe lymphocyte deficiencies can result in uncontrolled infections that can be fatal.
Higher than normal levels of lymphocytes is called lymphocytosis. Lymphocytes help fight of disease so can increase in cases of bacterial and viral infection as a normal physiological process. The most common cause of lymphocytosis is a viral infection. They can however, also be raised due to an autoimmune disorder causing chronic inflammation, leukaemia, lymphoma. If you have a high lymphocyte count your doctor may need to perform other tests to determine the cause.
A low lymphocyte count is called lymphocytopenia or lymphopenia. The most common cause of decreased numbers of lymphocytes is viral infections (including AIDS) and undernutrition. Lower levels can also be due to steroid medication, stress, chemotherapy, and malignant disease such as Hodgkin’s and Non-Hodgkins lymphoma.