Neutrophils Explained: What They Are and How They Function

Neutrophils are the most abundant type of white blood cells in the bloodstream, serving as the body's first line of defense against invading pathogens. These cells play a crucial role in the immune system, performing various actions to protect the body from foreign agents, particularly infectious ones.

Neutrophils: What Are They?

Neutrophils, often called polymorphonuclear leukocytes, are unique white blood cells recognizable by their distinctly segmented nucleus. This nucleus is typically divided into three to five lobes, connected by thin strands of nucleic material. Interestingly, the number of lobes in the nucleus increases as the neutrophil ages – young neutrophils may have only two lobes, but this can grow to five in older cells.

Like all blood cells, neutrophils are produced in the bone marrow. They play a crucial role in our immune system due to their strong phagocytic activity, which means they can engulf and destroy between five to twenty bacteria throughout their lifespan. This lifespan is usually short, lasting just one to two days. Neutrophils function similarly to tissue macrophages, primarily acting in the bloodstream. However, they can also move to areas outside the blood vessels, particularly those damaged or infected, to combat infections.

One of their key mechanisms is digesting cellular or molecular antigens. They achieve this by releasing lytic enzymes from their granules. Beyond engulfing and digesting microorganisms, debris, and cells that are old, infected, or transformed, neutrophils also secrete specific chemicals. These include pyrogens, which are responsible for causing fever, and various mediators that contribute to the inflammatory response. This multifaceted function makes neutrophils a vital component of our body's defense system.

How Neutrophils Function

Neutrophils perform their protective function through a series of steps:

  1. Chemotaxis: Neutrophils swiftly move towards the site of an infection. This is a key feature of their function in the immune response.
  2. Phagocytosis: Upon reaching, they engulf harmful invaders like bacteria. This is a critical step in neutralizing threats to the body.
  3. Microbicidal Activity: These cells then break down and destroy the engulfed pathogens. This process is crucial for eliminating the infection.

These activities are made possible thanks to the enzymes contained in their primary and secondary granules, the unique structure of the cytoplasmic membrane, and the presence of receptors for immunoglobulins G (IgG antibodies) and complement proteins.

Under normal conditions, mature neutrophils migrate into the bloodstream, where they remain for a relatively short time (6-12 hours), depending on various needs of the body (fever, stress, infections, etc.). After this period, these white blood cells become confined in the tissues, where they stay for a few days before dying.

Neutrophil Alterations

Alterations in neutrophils can involve either excess or defective numerical changes and can be primary or acquired.

  • Primary forms can result from genetic mutations causing a defect in the production, distribution, or function of neutrophils.
  • Acquired or secondary forms can result from infections, parasitosis, necrosis and tissue damage, allergic manifestations, and the intake of certain drugs.

Neutrophil Analysis

Examining neutrophils is a key part of a comprehensive blood test, which includes a white blood cell count. This test is commonly used to check a patient's overall health. By counting and examining the shape and structure of neutrophils, doctors can help diagnose various health issues that may impact these white blood cells. These issues include:

  1. Infections from bacteria, viruses, fungi, or parasites.
  2. Inflammatory conditions.
  3. Allergic reactions.
  4. Cancerous growths (neoplasms).
  5. Factors affecting their production and lifespan, such as immune disorders, autoimmune diseases, or exposure to harmful drugs or chemicals.

Furthermore, monitoring neutrophils is essential for tracking the progression of certain diseases and evaluating how well the body is responding to treatments. This is particularly important in treatments that might harm white blood cells or affect the bone marrow's function.

Normal Values and Abnormalities

Under usual circumstances, neutrophils make up about 40% to 75% of the nucleated cells in our circulating blood. When their count falls outside the normal range, which is between 1,500 and 7,000 per cubic millimeter of blood, it's considered atypical.

An elevated count of neutrophils, known as neutrophilia, happens when their numbers surpass this standard limit. Various conditions can lead to neutrophilia, such as bacterial infections, inflammation, surgeries, tissue death, allergies, and certain inflammatory disorders.

A low neutrophil count, on the other hand, termed neutropenia, is when these cells are fewer in the bloodstream. This decrease can be due to inherited conditions, diseases acquired over time like aplastic anemia, or specific infections. Neutropenia is also a common adverse effect of certain medications, notably those used in chemotherapy for cancer. This problem can originate from two main sources: either an issue with the production or a change in the synthesis of neutrophils in the bone marrow (upstream), or an increased breakdown of these cells (downstream). A lower count of neutrophils weakens the body's defense against infections, particularly those caused by bacteria.


Neutrophils are an essential component of the immune system, serving as the first line of defense against pathogens. Understanding their function, normal values, and possible abnormalities can provide valuable insights into the body's immune response and overall health. It's important to remember that any abnormalities in neutrophil count should be evaluated by a healthcare professional to identify and address any underlying health conditions.

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