Neutrophils and Neutropenia

Neutrophils are a type of white blood cell that is central to our immune system. As part of our innate immune defense, neutrophils act as the first-line responders to infection, attacking bacteria, viruses, and other pathogens.

Neutrophils can also be referred to as phagocytes (phago- meaning to eat, and -cyte meaning cell), since they protect the body by ingesting invading organisms. They are produced in the bone marrow and account for around 50 to 70 percent of your total white blood cells.

What Neutrophils Do

As a defensive immune cell, neutrophils have high motility (meaning the ability to move spontaneously) and are able to surround an infective agent to neutralize it. In addition to ingesting the pathogen, neutrophils can release cytotoxic (cell-killing) substances that directly destroy a foreign organism.

Neutrophils are able to find their prey through a process called chemotaxis wherein they recognize the chemicals released by a cut or scrape and move toward that "scent" automatically.

This is unlike second-line adaptive immunity, which produces cells tailored to kill a specific pathogen and that pathogen alone. Innate immunity, by contrast, kills non-specifically, attacking anything that doesn't "smell" right.

Neutrophils respond to infections both inside the body and on the surface of the skin. Pus, one of the byproducts of a skin infection, is mainly comprised of dead neutrophils, bacteria, and skin cells.

What Neutrophil Counts Tell Us

Neutrophils are counted as part of a complete blood count test (CBC). Another test, called the WBC differential, outlines the percentage of each type of white blood cell in a sample of blood, including neutrophils, lymphocytes, monocytes, basophils, and eosinophils.

Meanwhile, the absolute neutrophil count (ANC) tells us how many of these cells are in the blood. The test has a "normal" reference range of between 1,800 and 7,800 cells per microliter (μL).

A high neutrophil count, known as neutrophilia, can be caused by any infection, trauma, or inflammation that spurs the immune system to action. Neutrophilia is common with appendicitis, serious burns, certain types of leukemia, or any condition that causes acute inflammation (such as a heart attack).

By contrast, a low count, known as neutropenia, may be caused by sepsis, chemotherapy, radiation treatment, and certain autoimmune disorders. In some people, neutropenia can be chronic (ongoing and persistent), while for others it will be transient (usually in response to a disease or drug exposure).

Monitoring Neutrophils in Cancer Treatment

During cancer treatment, the absolute neutrophil count is routinely checked to determine how the immune system is responding to the pressure of radiation or chemotherapy. Neutropenia is relatively common in these circumstances and can be classified as:

• Mild neutropenia (ANC under 1,500 cells/μL), which carries a minimal risk of infection.
• Moderate neutropenia (ANC between 1,000 and 500 cells/μL), which poses a moderate risk of infection.
• Severe neutropenia (ANC under 500 cells/μL), which poses a severe risk of infection.

If the ANC drops below about 500 cells/μL, your doctor will likely prescribe medications to better normalize neutrophil levels and may also give you a course of antibiotics to prevent serious infection.