Definition of White Blood Cells (WBCs)

Types and Function of White Blood Cells

diagram showing the different types of white blood cells
What are white blood cells?. A.D.A.M. Medical Encyclopedia

Definition: White Blood Cells (WBCs)

White blood cells (WBCs)are a part of the immune system that helps fight infection and defend the body against other foreign materials.

Types of White Blood Cells

There are several different types of white blood cells, including lymphocytes, granulocytes (neutrophils, eosinophils, basophils), and monocytes.

Formation of White Blood Cells

White blood cells begin in the bone marrow in a process called hematopoiesis.

 All blood cells - white blood cell, red blood cells, and platelets, descend from a common hematopoietic stem cell, or "pluripotent" stem cell.  These stem cells evolve (differentiate) in different stages.  

The HSC cell first separates into the lymphoid cell line, via a lymphoid stem or progenitor cell gives rise to lymphocytes - specifically B lymphocytes or "B cells" and T lymphocytes or "T cells.  Progenitor stem cells also give rise to myeloblasts, which further differentiate into the cells that become red blood cells, that agranulocyte white blood cells, and platelets.

The myeloid cell line gives rise to macrophages, monocytes, neutrophils, basophils, and eosinophils.

White Blood Cell Lab Values

A normal white blood cell count is usually between 4,000 and 10,000 cells/mcl

Conditions Involving Elevated White Blood Cell Counts

Though you may think of infections, there are many causes of an elevated white blood cells count.

 These can be increased by overproduction, or rather by the body releasing white blood cells early from the bone marrow.  In severe infections, young appearing white blood cells, called blasts, often appear in the blood due to the body's attempt to get as many white blood cells on the scene as quickly as possible.

 Some causes of an increased white blood cell count include.  Stress of any form can also result in this release of white blood cells.

  • Infections
  • Cancers such as leukemias, lymphomas, and myelomas in which a greater number of white blood cells are manufactured.
  • Inflammation such as inflammatory bowel disease and autoimmune disorders
  • Trauma ranging from fractures to emotional stress
  • Pregnancy - In pregnancy, the number of white cells is "normally" elevated
  • Asthma and Allergies - With allergies, you will often see an increase in the type of white blood cells known as eosinophils
  • Exercise

Conditions With Low White Blood Cell Counts

Conditions which may result in a low white blood cells count include:

  • Severe infections
  • Bone marrow damage or disorders including aplastic anemia, bone marrow "takeover" by blood cancers or metastatic cancer, or drug or chemical related damage to the bone marrow
  • Autoimmune diseases such as lupus
  • Splenic "sequestration" where white blood cells are accumulated in the spleen.

    Symptoms of a Low White Blood Count

    The symptoms of a low white blood count can be understood by knowing the function of white blood cells.  Our white blood cells are our bodies defense against infections.  Some of the cells are part of our innate immune system, meaning they know from birth to attack foreigners, and others are part of our humoral, or learned immune system, and manufacturer antibiodies after "seeing" a germ in order to be prepared for another attack by that germ ahead of time.  Symptoms of infection may include:

    • Fever
    • Cough
    • Pain or frequency of urination
    • Blood in the stools
    • Diarrhea
    • Redness, swelling, or warmth in a region of infection

    White Blood Cells and Lung Cancer

    With lung cancer, chemotherapy can decrease the number of white blood cells produced by the bone marrow and increase the risk of an infection. Oncologists order a complete blood count (CBC) before and after chemotherapy to check on the number of WBCs.

    Also Known As: leukocytes

    Examples: After his chemotherapy treatment, John was told that his white blood cell count was low and that he should try stay away from people that are sick for a few days to reduce his risk of infection.


    U.S. Library of Medicine. MedlinePlus. White Blood Cell Count. Updated 02/02/16.

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