Neutrophils: Function, Anatomy, Structure, Immune System, Counts and Importance

They are white blood cells that protect us against bacterial infections, among other functions.

About 40 to 60 percent of white blood cells are neutrophils. These cells are the first to arrive on the scene when we experience bacterial infections.

Damage to cells results in the release of ” chemokines ” that attract neutrophils to the site in chemotaxis. Neutrophils may be best known to the casual observer as the main component of pus.


Neutrophils make up the most significant fraction of blood cells produced by the bone marrow. They are our “first responders” who play the role of the first line of defense against infectious organisms that enter our bodies.

They target foreign invaders by “eating” them, a process known as phagocytosis, or by bringing them into the cell in a process called endocytosis.

Once the foreign organism is inside the neutrophil, it is “treated” with enzymes that destroy the organism. Neutrophils also help regulate the immune response in general.

These cells have a very short lifespan, averaging only 8 hours, but our bodies produce approximately 100 billion of these cells each day.


After being released from the bone marrow, about half of these cells are present along the lining of the blood vessels, and the other half is found in the body’s tissues.

Anatomy and structure

Neutrophils can be seen under the microscope as cells, with a characteristic 2 to 5 lobes in the nucleus and staining pink or purple with neutral tints. The term “PMN” or polymorphonuclear leukocyte refers to this finding.

Neutrophils, White Blood Cells, and the Immune System

It can be confusing if you hear about white blood cells and neutrophils. If neutrophils are just one type of white blood cell, why do oncologists talk about a low white blood cell count and a low neutrophil count interchangeably with chemotherapy?

A simple answer is that low neutrophils, in particular, can be more dangerous in predisposing people to infections.

All blood cells (white blood cells, red blood cells, and platelets) form in the bone marrow, the spongy tissue in the central area of ​​the bones, such as the hips.

All of these cells originate in the bone marrow as a type of cell known as a hematopoietic stem cell.

These stem cells then differentiate from the different types of cells in a process known as hematopoiesis.

Since all of these cells start with a standard stem cell, processes that damage the bone marrow, such as chemotherapy, often affect all the different types of blood cells. This is known as chemotherapy bone marrow suppression.

In addition to red blood cells and platelets, there are several types of white blood cells. White blood cells develop along two different lines.

A stem cell can develop along the lymphoid line, resulting in the eventual formation of T and B lymphocytes or the myeloid line.

A cell in the myeloid line can become a neutrophil, an eosinophil, a monocyte, or a basophil.

Neutrophils start as myeloblasts, mature into promyelocytes, myelocytes, metamyelocytes, bands, and then mature neutrophils.

Neutrophil count

An average or absolute ANC neutrophil count is usually between 2,500 and 7,500 neutrophils per microliter.

Neutrophil levels below 2500 are known as neutropenia, although the degree of decline is significant. A count less than 1000 is the most serious and can predispose someone to infections.

Your blood count report can break down neutrophils into two categories which can be segmented (also known as mature) neutrophils and immature neutrophils, known as banding.

In severe infections, the bone marrow is stimulated to release more banded neutrophils (immature neutrophils), resulting in a high number of bands in your report.

Conditions with an abnormal number of neutrophils

When doctors monitor a complete blood count (CBC) or a white blood cell count (WBC), the most common abnormality increases or decreases in the expected number of neutrophils.

Neutrophil testing is, therefore, an essential part of evaluating the disease in the laboratory.

Causes of neutrophilia

Thinking about the function of neutrophils makes an increase in the number easier to understand. Mechanisms that can increase the number of these white blood cells include:

  • Reactive: With reactive neutrophilia, there is an increase in these blood cells in response to infection or stress. The stress hormones in our body cause more than expected amounts of these cells to be released from the bone marrow.
  • Proliferative (increased production in the bone marrow): This type refers to an increase in the number of neutrophils caused by their production in the bone marrow. This is most commonly seen with cancers, such as acute myeloid leukemia.
  • Demargination: Neutrophils often “live” attached to the lining of blood vessels. These neutrophils can become “demarcated” and circulate in the bloodstream due to stress, infection, and sometimes exercise.
Conditions that can cause neutrophilia

Some specific causes of an increased neutrophil count (neutrophilia) include:

  • Infections
  • Stress .
  • Blood cell-related cancers such as leukemia.
  • Autoimmune disorders such as rheumatoid arthritis.
  • Trauma and burns.
  • Of smoking.
  • The pregnancy.
  • Thyroiditis.
  • Eclampsia.

Immature neutrophils in the blood

Most of the neutrophils in our blood are mature. Immature neutrophils can be found in a blood smear if the body is stressed and there is a great need for more neutrophils.

When this occurs, a more significant number of immature neutrophils can reach the blood of the bone marrow before reaching maturity. Your doctor may mention that you have a more substantial number of bands, or even less mature neutrophils, in your blood count.

Alternatively, increased production of immature neutrophils may occur with leukemia, such as acute promyelocytic disease.

Causes of neutropenia

Your neutrophil count may be lowered on its own or reduced instead, along with other types of blood cells.

The term pancytopenia refers to a reduction in blood cells in three main types of blood cells; red blood cells (called anemia), platelets (called thrombocytopenia), and white blood cells.

Mechanisms that can result in a low neutrophil count can include:

  • Decreased or absent bone marrow production: for example, when the bone marrow is damaged as with chemotherapy, or there is a vitamin deficiency causing inadequate production.
  • Bone marrow infiltration: when the bone marrow is “taken up” by cells such as cancer cells.
  • Demand for more neutrophils: for example, fighting infection or responding to trauma. Initially, with most bacterial infections, the neutrophil count increases. However, with severe conditions, a low neutrophil count can occur because the disease can overwhelm the immune system.
  • Decreased Neutrophil Survival: While infections generally lead to increased neutrophil count, overwhelming infection, as well as infections with some viruses and rickettsial diseases, can lead to reduced neutrophil survival and a low count.
  • Neutrophils can also face immune destruction due to antibodies directed against themselves in conditions like lupus.
  • Destruction of neutrophils already produced.
  • Neutropenia cíclica.

Conditions that can cause neutropenia

Through the above mechanisms, a reduced neutrophil count could be due to:

  • Chemotherapy.
  • Aplastic anemia.
  • Radiation exposure.
  • Myelodysplasia.
  • Blood-related cancers that infiltrate the bone marrow, such as leukemia.
  • Viral infections
  • Overwhelming infections (sepsis).
  • Rickettsial Infections.
  • Typhoid fever.
  • Hypersplenism
  • Drug reactions, for example, to penicillin, ibuprofen, and phenytoin.
  • Hyperglycemia
  • Vitamin B12 deficiency (megaloblastic anemia) and folic acid deficiency.
  • Kostmann’s neutropenia (a genetic condition that affects young children).
  • Idiosyncratic (meaning that no one knows why the neutrophil count is low).

Importance of a low neutrophil count

The severity of a low neutrophil count depends on several factors, especially the degree of neutropenia. You are probably familiar with “bubble babies” stories – children born with severely compromised immune systems, but there are many grades in between.

A low neutrophil count is one of the severe side effects of chemotherapy. When these cells are limited in number or function or both, our bodies are less able to fight infections, even with bacteria that generally do not cause serious infections.

Examples:  Olivia’s neutrophil count was low after her chemotherapy treatment, so her oncologist recommended that she start antibiotics to prevent infection.