White blood cells (WBCs), also called leukocytes, are cells that circulate in the blood and the lymphatic system that help protect the body against infections. They are an important part of the body's immune system and also have a role in inflammation, allergic responses, and protection against cancer. There are five types of white blood cells, each with different functions. A WBC differential totals the number of each of the different types of WBCs in a person's sample of blood