Understanding eosinophils and eosinophilic asthma

The airways are a series of branching tubes that move air into and out of the lungs. The largest airway is the trachea (commonly called the windpipe).

The trachea branches into two smaller pipes called bronchi, which lead into the left and right lungs. The bronchi branch off into narrower and narrower airways. This structure is sometimes called the bronchial tree—think of the windpipe as the trunk, the bronchi as large branches, and the narrowing airways as thinner branches.

The smallest airways are the bronchioles, which end in small air sacs called alveoli. The walls of the alveoli are surrounded by very small blood vessels and allow oxygen to move into the blood and carbon dioxide to move out of the blood.

Asthma and the airways

Asthma is a condition that causes inflammation, excess mucus production, and narrowing of the airways. This makes it difficult to breathe. During an asthma flare, a person will have a hard time breathing in, but they will often find it more difficult to fully breathe out. Coughing, wheezing, and tightness in the chest are other common symptoms. However, asthma symptoms and severity vary from person to person.

Asthma inflammation can be understood as an overreaction by the immune system. As the body encounters allergens, irritants, emotional stress, or other triggers, the body releases chemicals that promote inflammation.

Keep in mind that this is a simplified explanation. The underlying mechanisms of airway inflammation in asthma are complex. Also, like the symptoms that result from asthma, the processes taking place at the cellular level can vary from one person to another.

Eosinophils and eosinophilic asthma

Eosinophils are one type of immune cell associated with asthma inflammation. Eosinophils are a type of white blood cell that help protect the body from parasitic infections and play an active role in immune responses.

When activated, eosinophils release inflammatory mediators, natural chemicals that control the body’s inflammatory response. This helps the body attack a parasite, but if eosinophils numbers are elevated or the immune response is overactive, problems can occur.

Normally, the body contains a relatively low number of eosinophils, which account for less than 7 percent of the total number of circulating white blood cells in the body. Elevated levels of eosinophils are associated with several health conditions, including atopic dermatitis, allergic rhinitis, and asthma.

While increased eosinophils can be detected in most cases of asthma, some people with asthma have much higher amounts of eosinophils than others. This is known as eosinophilic asthma, also called eos-asthma or e-asthma. This is common in people who are diagnosed with asthma as adults, and it is associated with more severe asthma.

A healthcare provider may determine a person has eosinophilic asthma based on medical history, pulmonary function tests, blood and sputum tests, fractional exhaled nitric oxide (which detects airway inflammation), and biopsies that test airway tissue or fluid in the lungs. A healthcare provider may also order tests to rule out other conditions.

When is asthma severe asthma?

Asthma can be categorized as severe when it is difficult to control with standard medications. Signs that asthma is not under control include frequent daytime and/or nighttime symptoms, the need to limit normal activities, frequent rescue inhaler use, and having to visit an emergency room or urgent care for asthma treatment.

Treating severe asthma often requires higher doses of inhaler medications and medications for long-term control. People with severe asthma may be candidates for biologic therapies, medications that target underlying inflammatory processes in the body associated with asthma. Most biologics are administered as subcutaneous injections.

Before starting any medication, have clear instructions on how to take that medication. You should always discuss precautions, potential drug interactions, and potential side effects with a healthcare provider before starting any medication.