The role of eosinophils in our immune system

What Is an Eosinophilic Disease?

Everyone has eosinophils in their body, a type of white blood cell that plays an important role in the immune system, helping to fight off certain infections and accumulating at the site of allergic reactions.1,2 At normal levels, eosinophils form a complex network with other cells to help protect the human body and keep us healthy.

In most healthy people, eosinophils make up less than five percent of the body’s white blood cells. However, too many eosinophils in the bloodstream, tissues or organs may cause health problems for some people. The diagnosis depends on where the eosinophils are found.3

When a person has a higher percentage of eosinophils without a known cause, they may have an eosinophilic disease, which can sometimes cause severe symptoms and significantly impact their life.3

A majority of patients (74-84%) with severe asthma may have an eosinophilic phenotype as determined by routine blood test. Patients with severe eosinophilic asthma are often prone to having recurrent exacerbations.

How Eosinophils Can Contribute to Disease

Asthma is a chronic lung disease where inflammation in the lungs causes the airways to narrow. Not all asthma is the same, and for some people, including those with severe asthma, elevated eosinophil levels can be a key factor.4 Eosinophils become activated during certain immune responses and release granule proteins that can promote inflammation. In people with severe asthma, the increased number of these cells can cause swelling of the airways and reduced airflow, making it very difficult to breathe and increasing the risk of an asthma attack.5

Eosinophilic granulomatosis with polyangiitis (EGPA), previously called Churg-Strauss Syndrome, is a rare chronic condition that causes inflammation of the blood vessels (known as vasculitis) and affects an estimated 5,000 people in the U.S.6,7 EGPA is characterized by the development of asthma as an adult, and an elevated blood eosinophil count. Some patients may also have allergies and growths in the nose called nasal polyps. While almost all EGPA patients have asthma, the symptoms people experience with EGPA may vary greatly and may affect different organ systems such as the lungs, sinuses, and nerves. It can also affect the heart, gastrointestinal tract, reproductive organs, skin, and urinary system. Because the symptoms can be similar to other diseases, EGPA can be very difficult to diagnose and patients may need to see several doctors such as allergists, immunologists, pulmonologists, and rheumatologists, to confirm the diagnosis and ensure proper treatment.8

Hypereosinophilic Syndrome (HES) is another condition connected to increased levels of eosinophils. HES is also a rare and under-diagnosed disease that affects around 5,000 patients in the U.S.2 People with HES often have eosinophil levels three times greater than the normal, which causes inflammation and organ damage, and can significantly impact patients’ ability to function and complete day-to-day activities. Complications can range from fever and gastrointestinal issues to respiratory and cardiac problems and, if left untreated, can be life-threatening. However, it may take people years to reach a diagnosis, as the symptoms are often common in many other medical conditions.

Eosinophil-associated gastrointestinal disorders (EGID) are rare diseases in which the root cause is not known, however, food and environmental allergies may play a role. These include EoE, Eosinophilic Gastritis, EGE, Eosinophilic Duodenitis, Eosinophilic Enteritis and Eosinophilic Colitis.11

Eosinophilic esophagitis (EoE) is a chronic, allergic, inflammatory disease which occurs when eosinophils accumulate in the esophagus, causing injury and inflammation. This damage can make eating difficult or uncomfortable, and pose several symptoms such as poor growth, chronic pain and difficulty swallowing.9

Eosinophilic gastroenteritis (EGE) is a rare disease in which eosinophils cause injury and inflammation to the stomach and small intestine, leading to several gastrointestinal symptoms including malnutrition, abdominal pain, poor growth, weight loss, vomiting, nausea and diarrhea.10

GSK’s Commitment to Improving Life with Eosinophilic Diseases  

GSK has been an established leader in eosinophil research for over 25 years. We are currently supporting more than 26 studies worldwide across 24 countries to progress eosinophil science with a goal of treating more patients and targeting different eosinophil-driven diseases.

At GSK, we’re committed to further exploring the role of eosinophils and the effect they have on our health. Understanding what causes certain people to have higher levels of eosinophils brings us a step closer to earlier and more accurate diagnoses, and ultimately, to treatment options that may help people living with eosinophilic diseases.

Steve Yancey

A leader of medicine development on GSK’s respiratory team


[1] Asthma and Allergy Foundation of America. Eosinophilic asthma. Available online at: [Last accessed: April 2020].

[2] Rothenberg ME. Eosinophillia. N Engl J Med. 1998;338:1592-1600.

[3] American Partnership for Eosinophilic Disorders (APFED). What is an eosinophil-associated disease? Available online at: [Last accessed: April 6, 2020].

[4] Kerkhof M, et al.Thorax. 2018;73:116–124.

[5] Travers J, Rothenberg ME. Eosinophils in mucosal immune responses. Mucosal Immunol. 2015;8(3):464-475.

[6] Data on File DNG#2017N348628_00.

[7] United States Census Bureau. U.S. and World Population Clock. July 2017.

[8] APFED. (2020). APFED EGPA Brochure [Brochure]. Author. Retrieved July 17, 2020, from

[9] EoE. (2020, August 18). Retrieved October 21, 2020, from

[10] Eosinophilic Gastroenteritis Quick Facts. (2015, August 16). Retrieved October 21, 2020, from

[11] EOSINOPHILIC GASTROINTESTINAL DISEASES. (n.d.). Retrieved October 21, 2020, from