A high lymphocyte count is an indicator of infection, autoimmune disorders and some types of cancer, explains Mayo Clinic. Lymphocytes are a type of white blood cell.
The medical term for an elevated lymphocyte count is lymphocytosis, according to the American Association for Clinical Chemistry. Acute viral infection, such as chickenpox, hepatitis and cytomegalovirus, is one of the causes of lymphocytosis. Another cause is bacterial infections such as tuberculosis and whooping cough. Lymphoma and lymphocytic leukemia are two types of cancers that may cause an increased lymphocyte count.
B lymphocytes and T lymphocytes both help the immune system fight infection. Both types of lymphocytes help the immune system recognize and destroy harmful organisms, but each type does so in a different way. B lymphocytes identify invaders and mark them for destruction, while T cells identify targeted organisms and destroy them.
When someone has an infection, B lymphocytes produce antibodies that bind to the foreign substance and mark it for destruction. Once the infection clears, these antibodies remain in the immune system. If a person is exposed to the same organism at a later date, the immune system remembers the organism and may be able to stop a new infection from developing.