What leukocytes reveal about your immune system
Leukocytes, also known as white blood cells, are important cells of the immune system. Without these cells, our body would be defenseless against bacteria, viruses, and other harmful intruders, as they play a central role in defending against infections and foreign substances. But what happens when the number of white blood cells is not within a healthy range? Deviations in the number of white blood cells can indicate various health problems, such as a weakened immune system, bone marrow issues, autoimmune diseases, or even certain types of cancer. In this blog, we will inform you about what white blood cells are, the specific functions they perform, and what abnormalities in these values can mean. We will also provide insights into treatment options and practical everyday tips on how you can support your immune system.
Table of contents
- What are leukocytes?
- What functions do leukocytes perform?
- Measurement and normal values of leukocytes
- Symptoms of leukocyte abnormalities
- Leukocytes and diseases
- Treatment of leukocyte abnormalities
What are leukocytes?
Leukocytes are cells of the immune system found in the blood and tissues. They are referred to as white blood cells because, unlike red blood cells, they do not contain the red pigment hemoglobin and therefore appear white under the microscope. They are produced in the bone marrow.
They are responsible for protecting the body against infections and foreign substances. Unlike red blood cells, which transport oxygen through our blood, and platelets, which are responsible for blood clotting, white blood cells specialize in identifying and combating pathogens. There are different types of white blood cells, each with specific functions such as defending against bacteria, viruses, and other harmful substances (Britannica, 2024).
What types of leukocytes are there?
The following table provides an overview of the different types of white blood cells and their functions.
| Type | Functions |
|---|---|
| Neutrophils | Make up about 60–70% of leukocytes. Engulf and digest bacteria and fungi to protect the body. This process is called phagocytosis. |
| Eosinophils | Make up about 2–4% of white blood cells. Combat parasites and are involved in allergic reactions. |
| Basophils | Less than 1% of white blood cells. Release histamine and play a role in allergic reactions. |
| Lymphocytes | Make up about 20–40% of leukocytes. Include various cell types such as B cells, T cells, and natural killer cells, which respond specifically to certain pathogens and combat them. |
| Monocytes | Make up about 2–8% of leukocytes. Develop into macrophages that phagocytose foreign substances and support the immune system. |
Source: Nall, 2020
What functions do leukocytes perform?
As illustrated in the table above, the different types of white blood cells have highly specialized functions. Below are six key functions summarized:
- Detecting and combating pathogens: Leukocytes identify and destroy harmful invaders such as bacteria and viruses, thereby preventing infections and diseases.
- Supporting inflammatory responses: White blood cells help regulate inflammation by releasing substances that attract other immune cells. Acute inflammation plays an important role in the healing of damaged tissue.
- Production of antibodies: Some white blood cells, such as B cells (a type of lymphocyte), produce antibodies (e.g., immunoglobulin G or immunoglobulin E) that specifically target certain pathogens. These antibodies help protect the body from future infections.
- Destruction of infected cells: Some leukocytes detect and kill cells that have already been infected with viruses or other pathogens. This prevents the infection from spreading throughout the body.
- Removal of dead cells: Some white blood cells engulf and digest already dead cells and cell debris, keeping the tissue clean and promoting more efficient healing processes.
- Monitoring the body for signs of infection or abnormal cells: White blood cells scan the body for signs of infections or abnormal cells, such as cancer cells. If anything unusual is detected, they respond quickly and trigger an immune reaction.
Sources: Britannica, 2024
Measurement and normal values of leukocytes
White blood cells are measured using a complete blood count (CBC), which provides both the total number of white blood cells and a differential count, i.e., the percentage and absolute count for each type of white blood cell.
Normal values for white blood cells
The number of leukocytes can vary depending on age, sex, and general health status and typically ranges between 4,000 and 11,000 cells per microliter of blood. The body produces nearly 100 billion white blood cells every day (MedlinePlus, 2021).
Symptoms of leukocyte abnormalities
Abnormalities in the number of white blood cells may indicate health problems. While high leukocyte levels (leukocytosis) often point to infections, inflammation, or stress, low leukocyte levels (leukopenia) may signal a weakened immune system or bone marrow issues. Here are the main symptoms that may occur with such changes:
- Fever
- Fatigue and weakness
- Frequent infections
- Night sweats
- Weight loss
- Swollen lymph nodes
- Mouth ulcers and skin infections
These symptoms may suggest disorders of the immune system. If such symptoms occur, a doctor should be consulted to determine the exact cause (Cleveland Clinic, 2021).
Leukocytes and diseases
The number of white blood cells in the blood may be elevated or decreased in various diseases. The following conditions can cause such changes:
Conditions and diseases that lead to low leukocyte levels (leukopenia):
-
Bone marrow cancers:
Cancers such as leukemia—particularly acute myeloid leukemia—and lymphomas affect the bone marrow, where white blood cells are produced. As a result, the bone marrow produces immature or defective cells in excessive amounts, reducing the number of functional white blood cells. -
Infectious diseases:
Certain infections, especially viral ones like HIV and hepatitis, can reduce white blood cell counts because the viruses attack the bone marrow and inhibit leukocyte production, severely weakening the immune system. -
Bone marrow disorders:
Diseases such as aplastic anemia impair the bone marrow’s ability to produce enough white blood cells. In aplastic anemia, the bone marrow fails to produce sufficient blood cells, resulting in an overall decrease in all types of blood cells. -
Vitamin B12 deficiency:
Since vitamin B12 is involved in DNA synthesis and cell division, a deficiency can impair the production of white blood cells in the bone marrow, leading to a reduced leukocyte count. This may cause a general weakening of the immune system. -
Medications:
Chemotherapy drugs used in cancer treatment can impair the bone marrow, as they target rapidly dividing cells such as cancer cells as well as healthy cells in the bone marrow, leading to a reduction in leukocyte production.
Diseases that lead to high leukocyte levels (leukocytosis):
-
Infections:
Bacterial and viral infections are common causes of elevated leukocyte levels, as the immune system produces more white blood cells to fight off pathogens. Examples include pneumonia and urinary tract infections. -
Stress:
Physical or emotional stress can temporarily increase leukocyte counts. The body prepares for potential threats by activating the immune system. This response is part of the "fight-or-flight" reaction and can temporarily elevate leukocyte levels. -
Autoimmune diseases:
Autoimmune conditions such as rheumatoid arthritis and inflammatory bowel diseases (Crohn’s disease, ulcerative colitis) cause chronic inflammation. These inflammations continuously activate the immune system, which increases leukocyte levels. In rheumatoid arthritis, the immune system is constantly active to combat inflammation in the joints.
Sources: Tvedten & Raskin, 2011; Cleveland Clinic, 2021; MedlinePlus, 2021
Treatment of leukocyte abnormalities
The treatment of deviations in leukocyte levels strongly depends on the underlying cause and severity of the condition. Low levels (leukopenia) are treated with medications that stimulate the bone marrow to produce more leukocytes, such as growth factors (e.g., G-CSF). Infections require antibiotics or antiviral agents, while autoimmune diseases are treated with immunosuppressants or corticosteroids. High leukocyte levels (leukocytosis) are also treated according to the cause: infections are managed with antibiotics, and chronic inflammations and autoimmune conditions are treated with anti-inflammatory drugs and immunosuppressants. The specific treatment is always tailored to the individual and carried out in close cooperation with a physician (Cleveland Clinic, 2022; Smith, 2024).
Everyday advice
There are also various aspects in daily life that you should consider to support your immune system, with a healthy lifestyle playing a central role:
- A balanced, vitamin-rich diet, including foods high in vitamin B12 and essential minerals
- Regular, moderate physical activity
- Use of stress management techniques such as meditation, yoga, or breathing exercises
- Good hygiene practices, such as regular hand washing, can reduce the risk of infection
- Regular medical check-ups and blood tests can help detect and treat abnormalities in leukocyte count early
- Avoid smoking and consume alcohol in moderation
Source: Harvard Health, 2024
