White blood cells (WBCs) are categorized into five distinct types: neutrophils, monocytes, lymphocytes, eosinophils and basophils. Each type plays its own role in fighting viral, fungal, bacterial and parasitic infections. A low count of white blood cells in the body, called leukopenia, reduces immunity and leaves the body vulnerable to diseases.
According to the 'Oxford Handbook of Clinical Medicine," neutrophils are the most abundant white blood cells, ranging between 2,000 and 7,500 per cubic mm of blood. About 55 to 75 percent of the total WBC count in the blood is made up of neutrophils. They play a crucial role in fighting infection. They have a "C" shaped, segmented nucleus. Neutrophils have a tendency to stick to the blood vessel walls and block any germs that attempt to enter the bloodstream through an infection or a wound.
Lymphocytes produce antibodies as a part of the immune system response. The antibodies are secreted into the blood plasma to act against harmful bacteria and toxins. The antibodies induce the germs to join together in clusters, enabling the phagocytes to consume them. The limitation of lymphocytes is that they are able to identify only certain specific antigens in the bloodstream. The number of lymphocytes ranges between 1,300 and 4,000 per cubic mm of blood, which makes them the second most largely present cells after the neutrophils.
Monocytes are the biggest in size among the five types of white blood cells. Their numbers in blood fall between 200 and 800 per cubic mm of blood, accounting for about 5 to 8 percent of the total WBC count. Monocytes perform the role of tissue macrophages that eliminate foreign particles and act against the multiplication of germs that cannot be successfully combated by the neutrophils.
Eosinophils range between 40 and 400 per cubic mm of blood, forming about 2 to 5 percent of the total blood count. The key function of eosinophils is to act against parasites and any antigen complex present in the bloodstream. These cells are also known to be the cause of many types of allergic responses within the blood.
As per the Department of Immunology, the Lerner Institute in Cleveland, the functions of basophils are poorly understood. They are the least numbered white blood cells, ranging between 0 and 100 per cubic mm of blood, and constitute less than 1 percent of the total white blood count. Basophils secrete antibodies and anticoagulants. This limits any hypersensitive reactions within the blood. Basophils are commonly associated with immediate immune reaction against foreign particles in the bloodstream.