Eosinophils are a type of white blood cell that functions within the immune system. They are primarily known for defending the body against multicellular parasites, such as worms. Eosinophils also accumulate at sites of inflammation, especially those related to allergic reactions, where they release cytotoxic proteins and inflammatory mediators. Eosinophilia refers to an unusually high count of these cells, typically defined as an absolute eosinophil count greater than 500 cells per microliter of blood. Elevated counts signal an underlying medical condition that requires identification and treatment to reduce cell numbers and prevent potential tissue damage.
Understanding the Causes of Eosinophilia
Reducing elevated eosinophil counts requires accurately diagnosing the root cause, as treatment depends entirely on the trigger. Eosinophilia commonly results from three major categories of immune system activity. Allergic conditions are the most frequent cause, including asthma, seasonal allergies (allergic rhinitis), and eczema. In these cases, the immune response against a perceived harmless substance drives the overproduction and tissue migration of eosinophils.
Parasitic infections, particularly those caused by helminths (worms), are another significant global cause. The immune system mobilizes these cells specifically to combat these invaders. Certain drug reactions can also trigger a temporary, severe form of eosinophilia. Identifying and discontinuing the causative medication is often sufficient to resolve the high count in these drug-induced cases.
Targeted Pharmacological Treatments
Pharmacological intervention to reduce eosinophil counts is initiated after the underlying cause is identified and requires medical supervision. Corticosteroids are the first-line treatment for many forms of eosinophilia, particularly when the cause is allergic or inflammatory. Systemic corticosteroids, such as oral prednisone, rapidly suppress inflammation and decrease eosinophil production in the bone marrow, leading to a quick reduction in blood counts.
For localized conditions, such as eosinophilic esophagitis (EoE) or asthma, topical or inhaled corticosteroids are preferred to minimize systemic side effects. In EoE, a topical steroid formulation like swallowed fluticasone or budesonide directly targets accumulated eosinophils in the esophageal tissue. For severe forms of eosinophilic asthma or hypereosinophilic syndromes (HES), more targeted therapies known as biologics are available.
These biologic agents are monoclonal antibodies that interrupt the signaling pathways responsible for eosinophil production and survival. Drugs like mepolizumab, reslizumab, and benralizumab target Interleukin-5 (IL-5) or its receptor. IL-5 is a cytokine that governs the growth, differentiation, and release of eosinophils from the bone marrow. By blocking this signal, these therapies achieve a profound reduction in circulating eosinophil levels.
Environmental and Dietary Management Strategies
For eosinophilia associated with allergic diseases, lifestyle changes and environmental control complement medical treatments by reducing exposure to known triggers. Allergen avoidance is a primary strategy. This involves using air purifiers with HEPA filters to reduce airborne pollen and pet dander. Reducing house dust mites requires encasing mattresses and pillows in allergen-proof covers and washing bedding frequently in hot water. Addressing indoor mold exposure necessitates controlling humidity levels and ensuring prompt cleanup of any visible mold.
Dietary adjustments are highly relevant, especially for gastrointestinal forms of eosinophilia like eosinophilic esophagitis (EoE), which is driven by food antigens. Elimination diets, done under medical guidance, involve removing common food triggers to see if counts normalize.
Elimination Diets
The six-food elimination diet removes the most common culprits:
- Milk
- Wheat
- Soy
- Egg
- Nuts
- Fish/shellfish
A less restrictive approach, like the two-food elimination diet, often starts by removing only milk and wheat products. If counts decrease, foods are systematically reintroduced to pinpoint the specific trigger. The most effective dietary intervention focuses on removing the specific food antigen that activates eosinophils.