White blood cells (leukocytes) are types of blood cells that are a critical part of your immune system. Your immune system protects you from infections ad diseases. There are several types of leukocytes and your blood can be low in any one of them. Neutrophils, lymphocytes, and eosinophils are some of the most common.
You usually do not have to worry about your white blood cell count because your body naturally regulates it. However, if you have certain medical conditions, your leukocyte count can fall and you need to increase it. Most people show no symptoms until their leukocyte count is dangerously low.
This article discusses the treatments used to increase white blood cell count.