What do white blood cells do?
General information only. This article explains the basics and is not medical advice. For anything about your own health, talk to a doctor or other qualified professional.
Quick answer
White blood cells (leukocytes) are the blood cells that help the body fight infections and other invaders like bacteria, viruses, fungi and parasites. They’re part of the immune system, are made mainly in the bone marrow, and travel through the blood and lymph to wherever they’re needed.
The three kinds of blood cells
| Cell | Main job |
|---|---|
| Red blood cells | Carry oxygen |
| White blood cells | Fight infection |
| Platelets | Help blood clot |
White blood cells make up less than 1% of your blood, but they’re essential.
The five main types
| Type | Share of white cells (typical) | What it does |
|---|---|---|
| Neutrophils | ~50–70% | First responders; swallow bacteria and fungi |
| Lymphocytes | ~20–40% | B cells make antibodies; T cells destroy infected cells and coordinate defense |
| Monocytes | ~2–8% | Become macrophages that “eat” germs and dead cells |
| Eosinophils | ~1–4% | Fight parasites; involved in allergies |
| Basophils | <1% | Release histamine in allergic reactions |
How they fight
- Eating invaders: Some white cells surround and digest germs, a process called phagocytosis.
- Making antibodies: B cells produce proteins that tag invaders for destruction.
- Remembering: Some lymphocytes become memory cells, which is why you usually don’t catch some illnesses twice and why vaccines work.
- Inflammation: Redness, swelling and pus around a cut are signs white cells are at work.
White blood cell counts
A blood test called a complete blood count (CBC) measures white cells. A count outside the normal range can have many causes, such as infection, stress, medicines or other conditions, so only a doctor can interpret results.
Where they’re made
Most white cells are made in the soft bone marrow inside bones like the hips and spine. Lymphocytes also mature in the thymus, lymph nodes and spleen.
Sleep supports the immune system; see why sleep is important. For a serious complication of infection, read what sepsis is.
Sources
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