 Welcome to White Blood Cells. Leucocytes, or white blood cells, protect the body in various ways against disease. The red bone marrow stem cells, the hemocytoblasts, give rise to almost all the white blood cells. Some lymphocytes are formed in lymphatic organs. Five types of white blood cells are carried in the blood to sites of infection. These types are grouped mainly by cytoplasmic contents into two groups, granulocytes and agranulocytes. Granulocytes, the red blood cell-sized granulocytes, are short-lived about 12 hours and develop in the red marrow. Neutrophils, the most common white blood cell, the neutrophils comprise 54 to 62% of the leukocytes and are the first to arrive at an infection site to ingest bacteria, virus particles, fungi, or protozoa. The neutrophil nuclei may have 2 to 5 lobes. The cytoplasmic granules are usually very fine and too faint to observe. Acenophils, comprising only about 3% of the leukocytes, the acenophils have bilobed nuclei and uniform-sized cytoplasmic granules. They moderate allergic reactions and defend against parasitic worm infestations. Basophils, comprising less than 1% of the circulating white blood cells, the basophils are smaller than other granulocytes. They are easy to identify because of the numerous granules in the cytoplasm. They discharge their granules containing histamine and heparin into damaged tissue spaces to promote inflammation and blood flow to damaged areas. Agranulocytes, the agranulocytes lack granules in their cytoplasm. The two types of agranulocytes are monocytes and lymphocytes. Monocytes, comprising 2 to 8% of circulating white blood cells, monocytes are twice the size of red blood cells. Monocytes have oval or kidney bean shaped nuclei. They travel in the blood for about a day before exiting. The migrating monocytes are big eaters. They develop into macrophages that phagocytose, bacteria and debris in the tissues. Lymphocytes, these cells of immunity are only slightly bigger than red blood cells. They are easy to recognize due to the large nucleus that occupies most of the cell. These cells may live for years and comprise 25 to 33% of the white blood cell population. T cells may directly attack foreign and tumor cells. B cells produce antibodies to attack foreign cells or proteins. NK or natural killer cells are important in cancer prevention. In order for leukocytes to perform phagocytosis, they must be able to leave the circulation system. They move like amoebas in a process of cytoplasmic streaming called diapidesis. The normal white blood cell count is 5,000 to 10,000 per cubic millimeter. Acute infections may elevate the white blood cell count above 10,000. This is called leukocytosis. The flu and other viral infections and various poisonings may cause leukopenia, where the white blood cell count falls below 5,000. Congratulations! You have completed this learning activity.