Single nucleated cells are cells with a single nucleus in the peripheral blood. Single nucleated cells include two types of cells, one is lymphocytes and the other is monocytes. The lymphocytes are divided into two types, one is B lymphocytes and the other is T lymphocytes. B lymphocytes mature in the bone marrow, which have humoral immune function, and under the stimulation of antigen, B lymphocytes morphologically deformed will be transformed into plasma cells, which can produce secreted antibodies and thus perform humoral immune function; T lymphocytes mature in the thymus, which have strong cellular immune function and can directly kill pathogenic microorganisms or senescent cells that enter the body. Monocytes are a type of human leukocytes that escape from the blood to the tissues and become phagocytes, which can engulf senescent cells and cell debris, as well as various pathogenic microorganisms that enter the body.