330 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. Eosinophils Eosinophils make up only a small portion of the white blood cell count—about 1% to 3%. Eosinophils participate in many inflammatory processes, especially allergic reactions, and are capable of phagocytosis. They are particularly active in the presence of parasites and worms. Basophils Basophils are the least abundant type of white blood cells. They produce histamine, which induces an inflammatory response and summons more infection- fighting WBCs to a site of injury or infection. Basophils also produce heparin, an anticoagulant that prevents blood clotting. Basophils are often associated with allergic reactions and asthma. They also play an important role in T cell adaptive immune responses. Lymphocytes Lymphocytes are the second most abundant type of white blood cells in the body. There are three types of lymphocytes: T cells, B cells, and natural killer cells. More than 80% of lymphocytes are T cells. T cells and B cells have special protein receptors on their surfaces that allow them to recognize and form antibodies Neutrophils, eosinophils, and basophils are classified as granulocytes because they have granules in their cytoplasm. Lymphocytes and monocytes are classified as agranulocytes because their cytoplasm lacks granules. Generally, WBCs have a lifetime of 13–20 days. Unlike RBCs, WBCs have a nucleus. The nucleus of a WBC is visible under a microscope when exposed to Wright’s stain, a staining solution that scientists use to differentiate blood cell types. Staining can also reveal the presence of any granules. WBCs are classified by size, nucleus shape and color, and the color of any granules (Figure 11.8). Neutrophils Neutrophils are the most abundant type of white blood cells. They are also the most important component of the body’s immune system because they are the “first responders.” Neutrophils are active phagocytes and kill foreign invaders such as bacteria, viruses, and fungi. Neutrophils are vital to fighting infection therefore, a neutrophil deficiency is a potentially life-threatening condition. Bioengineering Red Blood Cells Since Roman times, scientists have been looking for viable substitutes for blood. Doctors and scientists have experimented with animal blood and animal milk. Even wine has been suggested as a possible alternative to blood. Researchers at the Université Pierre et Marie Curie in Paris, France, have been studying the possibility of manufacturing red blood cells from stem cells. These researchers were able to generate billions of RBCs from a single stem cell. The RBCs were then injected into the stem cell donor. The stem cells were treated with several different growth factors to stimulate them to develop into mature RBCs. After 5 days, the survival rate of the human-engineered RBCs was 94% to 100%. Of these RBCs, 41% to 63% were still alive after 26 days. This is similar to the survival rate of a normal RBC. This research is critical, especially when you consider how these engineered RBCs might be used. Each year, the American Red Cross alone distributes about 6 million units of RBCs. According to the World Health Organization (WHO), each year more than 90 million blood donations are made at hospitals, clinics, blood banks, and donation centers around the world. However, some of these donations come from paid donors. In addition, the majority of blood donations are made in high-income countries. Successful engineering of RBCs would limit dependence on paid donors, especially in low-income nations where voluntary donation is less common. Research continues, but this fi rst successful attempt holds promise for a new way to achieve an unlimited blood supply. Research Notes sit/Shutt erstock.com People who need blood replacement today are largely dependent on blood obtained from volunteers and paid donors.