There are several reasons for the increase of lymphocytes in patients: First, physiological factors: at the age of 4-6 days to 4-6 years, lymphocytes are mostly physiologically increased, which is normal. Second, infectious diseases: such as viral infections, like measles, rubella, varicella virus, hepatitis virus, coxsackie virus, adenovirus, cytomegalovirus, etc., as well as infections like whooping cough, Mycobacterium tuberculosis, brucella, etc., may cause lymphocytosis. Third, leukemia and neoplastic diseases: acute or chronic lymphocytic leukemia, lymphoma, etc., can cause lymphocytosis. Fourth, other: recovery from acute infectious diseases and rejection of transplantation may see lymphocytosis. In cases of aplastic anemia and granulocytopenia, the proportion of lymphocytes may also increase accordingly, but the absolute value of lymphocytes is usually not significantly increased.