White Blood Cells (Leukocytes) Types and Functions

What are white blood cells?

White blood cells or leukocytes are immune cells, which help protect against infections and foreign bodies. They appear in the blood and lymphatic system: the lymph, lymph nodes, liver, spleen and thymus. In the blood, they represent one of the three main blood cell types; the other two being red blood cells (erythrocytes) and platelets (thrombocytes).

Leukocyte word origin: from the Greek leukos = white and cyte, which refers to the cell.

White Blood Cells Functions and Types

White blood cells develop from the blood stem cells, which are produced in the bone marrow.

White blood cells produce antibodies, cytotoxins and enzymes, which destroy microbes, cancer cells, cellular debris and foreign bodies and thus help to keep the body clean ^[1]. The end result of leukocytes’ action is often the formation of pus — oozing from a wound, coughed up as mucus, leaked into the urine or collected in the body tissues as an abscess. Pus contains mainly leukocytes, microbes and dead body cells.

Chart 1 references: Emedicine ^[2]. Neutrophils, basophils and eosinophils are collectively known as granulocytes. Lymphocytes and monocytes are collectively known as mononuclear cells.

1. Neutrophils

Neutrophils fight against infections by ingesting microbes, mainly bacteria and fungi ^[2].

High neutrophil count (neutrophilia) occurs in most acute bacterial infections ^[3].

Low neutrophil count (neutropenia) can occur in typhoid fever, staph infections and tuberculosis ^[3].

2. Eosinophils

Eosinophils fight against large parasites, like intestinal worms. During allergic reactions, they secrete IgE antibodies, which attack allergens.

High eosinophil count (eosinophilia) occurs in infestations with intestinal worms, in allergic reactions, asthma, hypereosinophylic syndrome and connective tissue diseases (SLE) and Hodgkin lymphoma ^[3].

3. Basophils

During allergic reactions, basophils secrete histamine, which dilates the blood vessels.

High basophil count (basophilia) occurs in chronic myelogenous leukemia ^[3].

4. Lymphocytes

Lymphocytes fight mainly against viruses and cancer cells. Types of lymphocytes:

• B cells recognize viruses and then transform into plasma cells, which release antibodies against viruses.
• T cells and natural killer (NK) fight against cells infected by viruses and cancer cells by releasing toxins.

High lypmhocite count (lymphocytosis) occurs in certain types of leukemia, in viral infections, such as infectious mononucleosis, citomegalovirus (CMV) infection and hepatitis, and in whooping cough (pertussis) ^[3].

5. Monocytes

Monocytes move from the blood to the body tissues–mainly to the liver, lymph nodes and lungs–where they become macrophages, which ingest cell debris.

High monocyte count (monocytosis) occurs in infectious mononucleosis and in chronic infections, such as tuberculosis, bacterial endocarditis, brucellosis and syphilis, in malaria and in certain cancers ^[2,3].

Normal Blood White Cell Count (WBC)

Normal white blood cell count (WBC) = 4-11 x 10⁹/L or 4,000-11,000/µL ^[2]. (L = liter, µL = microliter)

High White Blood Cell Count (Leukocytosis)

High WBC is called leukocytosis. WBC is considered high when it exceeds 11 x 10⁹/L or >11,000/µL ^[2].

There are 4 main reasons for high WBC: infections, inflammation, adverse reactions to drugs and allergic reactions.

Causes of high WBC (in a rough order from mild to severe) ^[3,5]:

• Strenuous exercise
• Emotional stress
• Cigarette smoking
• Pregnancy and labour
• The absence of spleen after spleen removal
• Tissue death due to burns, severe trauma, surgery or myocardial infarction (heart attack), epileptic attack (seizures)
• Allergic reaction, asthma, hay fever
• Sickle cell disease
• Lymphoma (Hodgkin disease)
• Inflammation (rheumatoid arthritis, inflammatory bowel disease–Crohn’s disease and ulcerative colitis–, vasculitis); high WBC triggered by an inflammation is called reactive leukocytosis
• Bacterial infections, such as pneumonia, pertussis
• Hypersensitivity reaction to drugs ^[3]: antibiotics (minocycline), antiepileptic drugs (carbamazepine, phenobarbital, phenytoin), beta adrenergic agonists (albuterol), epinephrine (adrenaline), granulocyte colony stimulating factor, heparin, lithium, steroids (prednisone, prednisolone)
• The infection with the bacterium Clostridium difficile, sepsis, organ rejection after transplantation, solid tumors (WBC 50,000-100,000/µL, called leukemoid reaction)
• Leukemia, polycythemia vera, essential thrombocytosis, myelofibrosis (WBC > 100,000/µL, called hyperleukocytosis)

Low White Blood Cell Count (Leukopenia)

Leukopenia means low WBC, that is <4 x 10⁹/liter or <4,000/µL.

Lack of leukocytes in the body, such as in HIV/AIDS or during chemotherapy, increases the risk of infections.

Causes of leukopenia (in a rough order from mild to severe) ^[1,2]:

• Hyperthyroidism ^[6]
• Malnutrition, including vitamin B12 and folate deficiency, common in alcoholism
• Drugs: antibiotics, anticonvulsants, anti-thyroid drugs, captopril, chlorpromazine, clozapine, diuretics, H2 blockers (cimetidine, ranitidine), quinidine, terbinafine, ticlopidine
• Autoimmune disorders, such as systemic lupus erythematosus (SLE)
• Enlarged liver (hepatomegaly) or spleen (splenomegaly)
• HIV/AIDS
• Aplastic anemia
• Severe bacterial infections
• Severe allergic reaction (anaphylaxis)
• Bone marrow deficiency due to infection or cancer (leukemia, multiple myeloma, cancer metastases into the bones)
• Chemotherapy or radiation therapy for cancer

Symptoms of High or Low WBC

High or low white blood cell count can be associated with ^[4]:

• Fever
• Chills
• Malaise
• Fatigue
• Paleness
• Increased susceptibility for bleeding, bruising
• Weight loss (in cancer)