Eosinophils are a specific type of white blood cell produced in the bone marrow that circulates in the bloodstream and is part of the immune system. They defend against certain pathogens and are involved in allergic reactions. When a routine blood test, such as a complete blood count, reveals an elevated number of these cells, the condition is called eosinophilia. This elevated count signals that the immune system is actively responding to an underlying health disturbance. Lowering the eosinophil count requires identifying and addressing the root cause through targeted medical treatment and supportive lifestyle adjustments.
Understanding Eosinophils and Eosinophilia
Eosinophils perform a specialized function, primarily targeting large, multicellular invaders like parasitic worms (helminths). They accomplish this by releasing toxic proteins and reactive oxygen species stored in their granules directly onto the parasite’s surface. Eosinophils also contribute to allergic inflammation by releasing mediators, such as cytokines and chemokines, which recruit other immune cells to the reaction site.
In a healthy adult, the absolute eosinophil count typically ranges between 100 and 500 cells per microliter (µL). Eosinophilia is defined as a persistent count exceeding 500 cells/µL in the peripheral blood. This elevation is categorized by severity: mild (500–1,500 cells/µL), moderate (1,500–5,000 cells/µL), and severe (exceeding 5,000 cells/µL). High accumulation of these cells in organs and tissues can release toxic contents, leading to chronic inflammation and potential tissue damage, which characterizes eosinophilic disorders.
Identifying and Treating the Underlying Cause
Since eosinophils respond to a stimulus, the most direct way to lower their count is to diagnose and eliminate the underlying trigger. Diagnosis starts with a detailed medical history, including travel, medication use, and allergy symptoms, followed by targeted laboratory testing. Identifying the source of immune activation is the primary focus of medical management.
Allergic Conditions
Allergic conditions are a common reason for elevated eosinophils. Conditions like asthma, allergic rhinitis (hay fever), and atopic dermatitis (eczema) mobilize eosinophils in response to allergens such as pollen, dust mites, or pet dander. Treatment focuses on managing the allergy with antihistamines, inhaled corticosteroids, and allergen avoidance, which reduces the inflammatory signal prompting eosinophil production.
Parasitic Infections
Parasitic infection, especially by helminths (worms), is another major cause globally, particularly in areas with poor sanitation. Eosinophils combat these large organisms, and their numbers rise dramatically in response to infection. Diagnosis involves stool sample analysis to identify parasite eggs or larvae. Treatment consists of specific antiparasitic medications that eradicate the organism, leading to a rapid decrease in the eosinophil count.
Drug Reactions
Drug reactions, known as drug-induced eosinophilia, occur when the body mistakenly recognizes a medication as a foreign invader. Many drug classes, including certain antibiotics, non-steroidal anti-inflammatory drugs, and anti-seizure medications, can trigger this hypersensitivity response. Management requires discontinuing the offending medication under a doctor’s supervision, often resulting in a prompt resolution of the eosinophilia.
Serious Underlying Diseases
Less common, but more serious, causes include certain autoimmune disorders, such as inflammatory bowel disease, and specific hematologic malignancies like leukemia or lymphoma. These underlying diseases require specialized diagnostic procedures, such as bone marrow biopsy or advanced imaging. Treating these complex conditions with chemotherapy or immunosuppressive therapies subsequently lowers the eosinophil count.
Medical Interventions to Reduce High Levels
When eosinophilia is severe, persistent, or causing organ damage, specific medical interventions are necessary to directly reduce the cell count and mitigate inflammatory effects.
Corticosteroids
Corticosteroids, such as prednisone, are frequently the first-line treatment for rapidly lowering elevated eosinophil levels and controlling severe inflammation. These powerful anti-inflammatory medications suppress the immune system’s production and activation of eosinophils. They provide swift relief in conditions like acute asthma exacerbations or severe hypereosinophilic syndromes.
Biologics (Targeted Therapies)
For chronic or severe eosinophilic disorders, such as hypereosinophilic syndrome (HES) or severe eosinophilic asthma, targeted therapies known as biologics are increasingly utilized. A prominent class of these treatments includes Interleukin-5 (IL-5) inhibitors, which are monoclonal antibodies. IL-5 is a cytokine responsible for the growth, maturation, and survival of eosinophils in the bone marrow.
IL-5 Inhibitors
- Mepolizumab and reslizumab bind directly to the circulating IL-5 cytokine, preventing it from signaling to eosinophils.
- Benralizumab targets the IL-5 receptor located on the surface of the eosinophil itself.
By interrupting this signaling pathway, these biologics effectively stop the production and activation of new eosinophils, leading to a profound reduction in blood and tissue counts.
IL-4/IL-13 Inhibitors
Another biologic, dupilumab, targets the shared receptor component for Interleukin-4 (IL-4) and Interleukin-13 (IL-13), two other cytokines involved in Type 2 inflammation. Dupilumab is highly effective in treating conditions like eosinophilic asthma and eosinophilic esophagitis by inhibiting the migration of eosinophils into inflamed tissues. Blocking the entry of eosinophils into tissues can sometimes cause a temporary rise in the blood eosinophil count, known as transient blood eosinophilia.
Lifestyle and Environmental Management
Self-managed strategies complement medical treatment and help sustain lower eosinophil counts.
Environmental Control
Environmental control is particularly important when the underlying cause is an allergy, such as to inhaled allergens. Minimizing exposure to known triggers like dust mites, mold, and pet dander reduces the chronic immune activation that drives eosinophil production. This often involves using high-efficiency particulate air (HEPA) filters, maintaining low indoor humidity, and frequent cleaning of bedding.
Dietary Adjustments
Dietary modifications may be advised, especially if food allergies or eosinophilic gastrointestinal disorders are suspected. Elimination diets, where common food allergens are systematically removed and reintroduced, can help pinpoint triggers contributing to gut inflammation. While anti-inflammatory foods are beneficial for overall health, major dietary changes should be made in consultation with a physician or registered dietitian.
Stress Management
Chronic stress can influence the immune response and potentially contribute to inflammatory conditions. Stress management techniques are supportive, as they help regulate the body’s inflammatory signals. Engaging in mind-body practices like yoga, meditation, or deep breathing exercises works synergistically with medical treatments to promote overall immune balance.