Lymphocytes are divided into B-lymphocytes and T-lymphocytes, and mature B-lymphocytes and mature T-lymphocytes have different origins, with mature B-lymphocytes originating from the bone marrow and mature T-lymphocytes originating from the thymus.B-lymphocytes and T-lymphocytes become larger after antigen activation and then proliferate and differentiate, with B-lymphocytes differentiating into plasma cells that secrete antibodies, which perform the function of immunity, enabling T lymphocytes can be divided according to their function into cytotoxic T cells and regulatory T cells, which are able to exert a killing effect on virus-infected cells and tumor cells.