Neutrophils

Neutrophils (also neutrophil granulocytes) are white blood cells (leukocytes) – and thus a central component of the immune system in dogs. They are practically the body’s first response team: even before other defence mechanisms kick in, neutrophils react to infections and inflammations and attack bacteria, viruses and fungi. As part of the innate immune response, they simultaneously make up the largest proportion of all white blood cells in the blood – making them one of the most important cell groups overall.

What neutrophils do in the body

Neutrophils defend the body against pathogens in several ways:

1. Phagocytosis: Neutrophils take up pathogens into their cells and break them down. This process eliminates microorganisms quickly.
2. Release of enzymes and toxins: Special granules in neutrophils release toxic enzymes and proteins that kill pathogens and prevent their spread.
3. Neutrophil Extracellular Traps (NETs): Neutrophils release nets made of DNA and proteins that bind and immobilise bacteria. This prevents their multiplication and makes them susceptible to attack by other immune cells.
4. Recruitment of other immune cells: Neutrophils release chemical signals that attract further immune cells to the site of infection and strengthen the defence response.

Neutrophils in blood tests – what the values indicate

The blood count shows how many neutrophils are currently circulating. The neutrophil level is not an end in itself: it provides clear indications of inflammation, infections or other conditions that might otherwise remain hidden.

Neutrophilia – too many neutrophils in the blood:

• An elevated value usually means that the immune system is currently working at full capacity – whether due to an infection, an inflammation, but also through stress or, in the worst case, due to cancer (for example leukaemia).
• Typical triggers: bacterial infections, injuries, persistent stress, tumours and inflammatory diseases of various kinds.

Neutropenia – too few neutrophils in the blood:

• If the level drops too low, the dog loses a significant part of its infection defence. It becomes more sensitive to germs that would hardly affect a healthy animal. Often, a bone marrow disease, a severe infection or a specific medication is the cause.
• Known causes: viral infections, chemotherapy, autoimmune diseases or severe sepsis.

Neutrophils in infections and inflammations

As soon as an infection or injury occurs anywhere in the body, neutrophils migrate there as the first immune cells. To do this, they actively leave the bloodstream, penetrate the surrounding tissue and attack pathogens directly. The well-known picture – redness, swelling, warmth – arises precisely when neutrophils and other immune cells gather in large numbers at one location. You can see it when they are working.

The role neutrophils play in diseases

• Bacterial infections: Neutrophils are particularly effective here. A strong rise in values (neutrophilia) is therefore often a clear signal of a bacterial infection – vets use this specifically for diagnosis.
• Immunodeficiency diseases: Reduced neutrophil counts (neutropenia) indicate a weakened immune system. Affected dogs fall ill more frequently, struggle with recurrent infections and require particularly intensive care.
• Bone marrow diseases: Neutrophils are produced in the bone marrow. If this is affected – for example by leukaemia or other forms of blood cancer – production slows down, and mature, functional neutrophils become scarce.

Diagnostic significance

The differential blood count shows how many neutrophils are circulating in the blood – a test that is standard practice if there is suspicion of infections, inflammation or immune disorders. Altered values give the vet important clues: not only for diagnosis, but also for determining how treatment should proceed and whether it is effective.

Treatment for abnormal values

What is done depends directly on the cause – there are no blanket prescriptions here.

• Neutrophilia: If an infection is present in the background, antibiotics or anti-inflammatory medications are usually central to treatment. If cancer is the underlying cause, chemotherapy or another targeted therapy may be required.
• Neutropenia: To reduce the risk of infection, agents such as immunostimulants are used, supplemented by careful monitoring of the health status. For bone marrow diseases, therapy is based on the specific findings.