Plasma cells are B lymphocytes that secrete immunoglobulins (antibodies). The type of antibodies that these plasma cells produce depend on the cytokine that influences the secretion of these immunoglobulins. Their appearance (on light microscopy) is quite characteristic: they have basophil cytoplasm and an excentric nucleus, in addition to a pale zone in the cytoplasm that (on electron microscopy) contains an extensive Golgi apparatus. After dividing for around five days, mature B cells develop into plasma cells or an other type, Memory B cells. Memory B cells are formed specific to the antigen(s) encountered during the primary immune response; able to live for a long time, these cells can respond quickly upon second exposure to the antigen for which they are specific.