The life span of white blood cells varies depending on the service they have to perform. For example, the life span of B cells ranges from three or four days to up to five weeks. If a T cell has no function other than to travel throughout the body, it can last for months; if it is engaged in a battle with foreign substances, it will last a from a day or two to a week, depending on the circumstances.
White blood cells that are produced by marrow inside the bone are called leukocytes. White blood cells that are produced by lymph nodes in the lymphatic system are called lymphocytes.
There are three types of leukocytes: neutrophils, eosinophils and basophils.
Neutrophils attack and digest bacteria. They can survive three to four days, but after they digest bacteria, they die in about 12 hours.
Eosinophils stain parasites and foreign molecules and digest them. The three-week life span of eosinophils includes maturing, working and reaching their intended target.
Basophils merely stain molecules, but they are multiplied in the presence of leukemia. Basophils mature and perform their duties for a period of from three days to a week and a half.
Lymphocytes can live for as long as a month. Lymphocytes include B cells that produce antibodies and T cells that protect the body on a cellular level.
See Livestrong.com's Difference Between Red & White Blood Cells to learn more.