Lymphocytes are mainly divided into three categories: T cells, B cells and natural killer (NK) cells, which are the main immune cells of the body.
Normal reference value of lymphocytes: adults (0.8 to 4) × 10*9/L. The number of lymphocytes is affected by both physiological and pathological factors. Low lymphocytes include both absolute and relative decreases.
Any of the various causes that cause a significant increase in neutrophils can lead to a relative decrease in lymphocytes and a decrease in the lymphocyte ratio, but the absolute number is not reduced. Physiological conditions commonly include late pregnancy, childbirth, after strenuous exercise or labor, after a full meal or shower, and after high temperatures or severe cold, all of which can result in a high neutrophil ratio and a low lymphocyte ratio. Common causes in pathological cases are various infections, especially septic infections such as Staphylococcus aureus, Streptococcus haemolyticus, and Streptococcus pneumoniae infections, where laboratory tests will suggest that the neutrophil ratio will be high and the lymphocyte ratio low. High neutrophil ratios and low lymphocyte ratios are also seen in cases of severe tissue injury and massive blood cell destruction, such as severe trauma, after major surgery, massive burns, acute myocardial infarction, and severe intravascular hemolysis.
Absolute reduction of lymphocytes is common for several reasons: lymphocytopenia during recovery from influenza; HIV infection, which selectively destroys CD4+ cells leading to a marked reduction in CD4+ cells and an inverted CD4+/CD8+ ratio; tuberculosis, with a marked reduction in CD4+ cells in early lymphocytopenia, which can return to normal if treatment is effective; alkylating agents (cyclophosphamide etc.) can cause significant decrease in leukocytes, accompanied by a significant decrease in lymphocytes, and the decrease in lymphocytes can persist for several years after stopping treatment; radiation therapy can destroy lymphocytes, with each low-dose radiation therapy producing stronger destruction than 2 high-dose radiation therapy per week; immune diseases such as systemic lupus erythematosus, rheumatoid arthritis, mixed connective tissue disease, and polymyositis, due to antibodies producing anti-lymphocyte antibodies, resulting in lymphocyte destruction and decrease, and the degree of decrease is related to the titer of the antibody; congenital immunodeficiencies, such as various types of severe combined immunodeficiency, ataxia capillaris, malnutrition or zinc deficiency, can cause lymphocytopenia to varying degrees. Certain drugs can also cause lymphopenia, such as menadione, nitrogen mustard phenylbutyrate, cortisone, epinephrine, lithium, nicotinic acid, steroids, etc.
Therefore, it is not significant to diagnose the disease based on low percentage of lymphocytes in blood routine alone, but needs to be combined with clinical symptoms and other relevant laboratory tests.