Lymphocytes can enter mitosis when they are activated by mitogens or antigens. B cells specifically can divide when they encounter an antigen matching their immunoglobulin. T cells undergo mitosis when stimulated by mitogens to produce small lymphocytes that are then responsible for the production of lymphokines, which are substances that modify the host organism to improve its immunity. B cells, on the other hand, divide to produce plasma cells when stimulated by mitogens, which then produce immunoglobulins, or antibodies.  Mitogens are often used to stimulate lymphocytes and thereby assess immune function. The most commonly used mitogens in clinical laboratory medicine are:
Lipopolysaccharide toxin from gram-negative bacteria is thymus-independent. They may directly activate B cells, regardless of their antigenic specificity. Plasma cells are terminally differentiated and, therefore, cannot undergo mitosis.  Memory B cells can proliferate to produce more memory cells or plasma B cells.  This is how the mitogen works, that is, by inducing mitosis in memory B cells to cause them to divide, with some becoming plasma cells.