These cells also produce substances that modulate inflammation . These cells contain numerous granules that contain heparin and histamine and may mediate hypersensitivity reactions. Lymphocytes Lymphocytes are spherical cells with a diameter of 6-18 microns with a spherical nucleus and very little cytoplasm. Some large lymphocytes are thought to be memory cells that differentiate into effector T cells or B lymphocytes having specific antigen receptors on the cell surface. T cells participate in cellular immunity while B cells are involved in humoral immunity as they differentiate into plasma cells that make specific antibodies.
Lymphocytes vary in life span with some living only a few days while others ciculate for many years.
These cells are the only white blood cells that return to the blood stream after migrating to the tissues. These agranulocytes vary in diameter from 12-20 microns and have an oval, horseshoe or kidney shaped nucleus with more cytoplasm than lymphocytes. The nucleus does not stain as darkly as that of lymphocytes in blood smears. After leaving the ciculatory system, monocytes differentiate into macrophages in connective tissues . Platelets These cell fragments originate from large cells in the bone marrow called megakaryocytes, have a lifespan of about 10 days and are nonnucleated.