White blood cells

What are white blood cells (WBCs)?

Red blood cells, white blood cells (WBCs), platelets and plasma make up your blood.  Your blood contains only about 1% WBCs, but they play a critical role.

WBCs, or leukocytes, are immune system cells that protect the body against illness and disease.  Most people produce around 100 billion WBCs every day.

Bone marrow makes WBCs; blood and lymph tissues then store the WBCs.  Because some WBCs have a short life of 1 to 3 days, your bone marrow is constantly making them.  When an infection or inflammatory condition occurs, the body releases WBCs to help fight the infection.

There are several different types of WBCs.  Each type of WBC has a specific function in defending the body against infections.

Types of white blood cells

Among your WBCs are:

Lymphocytes: They create antibodies to fight against bacteria, viruses and other potentially harmful material.

Neutrophils: They kill and digest bacteria and fungi.  They are the most numerous of the WBCs and are the first line of defence against infections.

Basophils: They alert the body to infections by secreting chemicals into the bloodstream, mostly to combat allergies.  They secrete chemicals such as histamine, a marker of allergic disease, that help control the body’s immune response.

Eosinophils: They attack and kill parasites and cancer cells and help with allergic responses.

Monocytes: They have a longer lifespan than many white blood cells and help to break down bacteria.  When needed, monocytes travel to other organs, such as the spleen, liver, lungs and bone marrow where they transform into a cell called a macrophage.  A macrophage is responsible for many functions, including removing dead or damaged tissue, destroying cancer cells and regulating the immune response.

High and low white blood cell count

A high WBC count usually indicates that the immune system is working.  It indicates an allergic response, an inflammatory condition or fighting off an infection.  It can also be a sign of physical or emotional stress.  People with certain blood cancers may also have high WBC counts.  Surgical procedures that cause cells to die can also cause a high WBC count.

Your WBC count can be low for a number of reasons.  This includes when something destroys the cells more quickly than the body can replenish them.  Or, when the bone marrow stops making enough WBCs to keep you healthy.  When your WBC count is low, you are at great risk for any illness or infection.