White blood cells have a nucleus, but red blood cells do not. White blood cells play protect the body from disease and infection.
There are five types of white blood cells, which are divided into two main classes. Granulocytes make up the first class and are made up of neutrophils, eosinophils and basophils. Neutrophils have a multilobed nucleus, which means it has more than two lobes. Eosinophils are bi-lobed, which means they have only two lobes, and basophils can have either a bi-lobed or tri-lobed nucleus. Granulocytes are characterized by the presence of granules in the cell's cytoplasm, which is the substance that surrounds the nucleus.
Agranulocytes, or mononuclear leukocytes, make up the second class of white blood cells. This class consists of lymphocytes and monocytes. A lymphocyte has an eccentric nucleus while a monocyte has a kidney-shaped nucleus. Agranulocytes do not have granules in the cytoplasm, and the nucleus rarely has lobes.
The nucleus in white blood cells plays an important role, primarily because it contains important genetic information. Since these cells do not have hemoglobin, the red protein found in red blood cells, they are considered "white" and that is how the name was coined. White blood cells come in all different sizes, and the size is dependent on the size and function of the nucleus.