The causes of a low lymphocyte count include leukemia, steroid use, HIV infection and sepsis, according to MedlinePlus. Chemotherapy and radiation exposure also affect lymphocyte levels. A lymphocyte is a type of white blood cell.
The medical term for a low lymphocyte count is lymphocytopenia, reports the National Heart, Lung, and Blood Institute. Some people with lymphocytopenia do not produce enough lymphocytes. In some cases, the body manufactures the right number of lymphocytes but some of them are destroyed. Low lymphocyte count also occurs when lymphocytes get stuck in the lymph nodes or spleen instead of circulating in the blood.
Lymphocytopenia makes it difficult for the immune system to fight infections, states the National Heart, Lung, and Blood Institute. Someone with a low lymphocyte count may have repeated bacterial, fungal, parasitic or viral infections. These infections must be treated to prevent them from causing serious complications.
B lymphocytes and T lymphocytes help the immune system fight infection, according to the Cancer Alliance for Research, Education and Survivorship. B lymphocytes manufacture antibodies that attach to foreign substances called antigens. When an antigen and an antibody come together, the antibody tells T lymphocytes to destroy the antigen. T lymphocytes recognize and respond to antigens. These cells have the ability to destroy targeted cells and regulate the body's immune response.