White blood cells, also called leukocytes, are cells that exist in the blood, the lymphatic system, and tissues and are an important part of the body's defense system. They help protect against infections and also have a role in inflammation, allergic responses, and protecting against cancer. The white blood cell (WBC) count totals the number of white blood cells in a person's sample of blood. It is one test among several that is included in a complete blood count (CBC), which is often used in the general evaluation of a person's health