Eosinophils are a type of white blood cell. Chronic obstructive pulmonary disease (COPD) can lead to a high level of eosinophils in the blood, doctors call this eosinophilia. Also, eosinophils may contribute to inflammation and airway obstruction.

While the primary cause of COPD is smoking, other factors, such as air pollution, genetics, and respiratory infections, can also contribute to developing the disease. Eosinophilic airway inflammation is a common feature of COPD, and it is associated with increased exacerbations, reduced lung function, and a less positive quality of life.

This article explores the relationship between eosinophilia and COPD, including its consequences and potential treatments.

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Eosinophils play a crucial role in the immune system’s response to allergens, parasites, and certain infections. The normal range for eosinophil blood levels is typically between 0 and 500 cells per microliter (cells/µL). Eosinophilia typically means an eosinophil count greater than this, but doctors further classify it as:

  • mild (500 to 1,500 cells/µL)
  • moderate (1,500 to 5000 cells/µL)
  • severe (>5,000 cells/µL)

Lower levels of eosinophilia may still contribute to COPD exacerbation.

Experts also link COPD with eosinophilic inflammation. This refers to an accumulation of eosinophils in the lung tissues, that can lead to the release of inflammatory mediators and airway obstruction.

Doctors do not fully understand how COPD causes high eosinophil levels. However, they believe that the chronic inflammation in the airways of people with COPD stimulates the immune system to produce more eosinophils in an attempt to fight the cause.

Additionally, exposure to environmental pollutants and irritants — such as cigarette smoke — can further exacerbate the inflammation and immune response, leading to higher levels of eosinophils.

What are higher levels of eosinophils in COPD associated with?

Research has shown that higher levels of eosinophils in COPD are associated with various implications, including:

  • increased risk of future exacerbations
  • lower rate of intensive care unit (ICU) admission
  • shorter duration of mechanical ventilation, a type of therapy to treat COPD
  • higher early mortality but no difference in overall mortality

The prevalence of reported eosinophilia in COPD varies widely across studies and depends on the threshold used for evaluation. For example, in the WISDOM trial involving 2,420 people with COPD:

  • 53% of participants had ≥150 cells/µL
  • 20% had ≥300 cells/µL
  • 11% had ≥400 cells/µL

In another study involving nearly 40,000 people with COPD, the authors found that 34.9% had blood eosinophil counts of ≥340 cells/µL compared with 25.8% of people without COPD.

Eosinophilic inflammation

Likewise, the prevalence of eosinophilic inflammation varies depending on the specific population and definitions used. However, around 1 in 3 people with stable COPD have evidence of eosinophilic inflammation, a number that increases during COPD exacerbations states.

Stable COPD refers to mild symptoms that can be managed well with the regular use of inhalers. Exacerbations occur when symptoms intensify, and additional therapy, such as steroids, may become necessary.

Some experts suggest that people with eosinophilia and eosinophilic inflammation form a subtype of COPD.

Elevated eosinophil counts appear to predict how people with COPD might respond to inhaled corticosteroids (ICS). Doctors may therefore use eosinophilia as a biomarker to predict the success of ICS treatment.

Some research shows that in severe exacerbations of COPD requiring hospitalization, people with eosinophilia responded faster to treatment with shorter hospital stays. They also showed a lower rate of ICU admission.

Interestingly, people with high eosinophil blood counts tend to have more ICS withdrawal issues and increases in exacerbations when doctors stop their ICS therapy. However, other research has not confirmed these effects, and it may differ based on:

  • age
  • overall health status
  • smoking status
  • other factors

That said, the Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines recommend using an eosinophilia cutoff of >300 cells/μL as a predictor of ICS effects. Treatment decisions should also consider the benefits and risks of ICS on an individual basis.

Learn more about inhaled steroids here.

According to the GOLD guidelines, doctors should base their COPD treatment recommendations on a person’s respiratory symptom severity and history of exacerbations. They should not factor in pneumonia history or the presence of eosinophilia.

That said, some experts still believe it is important to consider these factors. For example, ICS treatment is traditionally a mainstay of COPD treatment but is becoming controversial. And in someone with COPD who has a high eosinophil count and no history of pneumonia, ICS could be a valuable part of their therapy. The treatment benefits may include:

  • improved lung function
  • reduced symptoms
  • decreased rate of exacerbations

It is unclear if ICS therapy is beneficial in people with COPD and low eosinophil counts with no pneumonia history. Doctors should evaluate the benefits and risks of treatment on a case-by-case basis, especially if the person has a high eosinophil count plus a history of pneumonia.

Treatment with mepolizumab — a monoclonal antibody directed against interleukin-5 (an inflammatory mediator) — may provide some benefit to people with eosinophilic COPD.

COPD is a chronic lung disease involving inflammation in the airways. Studies have shown that some people with COPD may have elevated levels of eosinophils, a type of white blood cell involved in the immune response.

Eosinophils may play a role in inflammation. Specifically, eosinophilic inflammation can lead to increased symptoms, exacerbations, and differing responses to bronchodilator treatment.

Doctors can use elevated eosinophil counts as a biomarker to predict how people with COPD will respond to treatment with inhaled corticosteroids (ICS). Treatment for COPD with eosinophilia may involve using medications that target eosinophilic inflammation and reduce airway inflammation, such as inhaled corticosteroids and biological agents.

However, treatment decisions should be made individually, considering the person’s symptoms, history, and other factors influencing treatment response.