Eosinophilia (eosinophilic leukocytosis) is an increase in the blood level of eosinophils more than 500 in 1 μl of blood or more than 5%. Most often occurs in allergic reactions, parasitic invasions, may indicate severe lung diseases, oncological hematological pathologies. There are no specific manifestations. The clinical picture depends on the disease in which there is an increased content of eosinophils. The level of eosinophils is examined in venous or capillary blood by counting the leukocyte count in the general blood test. To correct eosinophilia, it is necessary to treat the disease that caused it.
To date, there are two main classifications of eosinophilia - according to the level of increase in eosinophils and according to the etiopathogenetic factor. The following eosinophilias are distinguished by the number of cells:
Moderate and severe eosinophilia are combined by the term hypereosinophilia. According to the pathophysiological mechanism, eosinophilia is divided into:
Separately, transient (short-term) eosinophilia is isolated, which is not directly associated with specific diseases. The number of eosinophils may increase with the use of certain drugs (antibiotics, anti-tuberculosis drugs), the introduction of a vaccine against hepatitis A, during hemodialysis, exposure to local radiation therapy. The exact pathophysiological mechanism for the increase in eosinophils under these circumstances is unknown.
This is the most common cause of eosinophilia. Any hypersensitivity reactions are accompanied by an increase in the production of eosinophils by the bone marrow. The pathogenesis of eosinophilia in allergies is well understood. When an allergen enters the body (by inhalation, through the skin or mucous membranes), it interacts with IgE on the basophil membrane. This leads to their degranulation of the latter and the release of histamine, leukotrienes and other mediators, as a result of which allergic inflammation develops in the tissues, which causes symptoms from the skin (atopic dermatitis, urticaria), mucous membranes (allergic rhinitis, conjunctivitis), as well as respiratory systems (bronchial asthma).
In parallel with this, eosinophilic chemotactic anaphylaxis factor is released by basophils, which stimulates the migration of eosinophils from the peripheral blood to the site of inflammation. Eosinophils, in turn, suppress the production of allergy mediators. During the height of an allergic reaction (exacerbation), the level of eosinophilia is maximum; as symptoms resolve, it gradually decreases and normalizes into remission.
With a pronounced exacerbation, the content of eosinophils, on the contrary, can be reduced (eosinopenia) or even equal to zero (aneosinophilia). This happens when there has been a massive migration of eosinophils to the focus of allergic inflammation, and new eosinophils have not yet had time to be synthesized in the bone marrow. Also, if a secondary bacterial infection (bronchitis) joins during a relapse of bronchial asthma, then the eosinophil counts may remain within the normal range.
Mostly with allergies, a mild degree of eosinophilia occurs. For bronchial asthma, especially atopic and aspirin forms, moderate eosinophilia is characteristic. In allergic pathologies, an increased content of eosinophils is observed not only in the blood, but also in other biological fluids (in sputum and bronchoalveolar fluid - with bronchial asthma, in nasal mucus - with rhinitis, in scrapings from the conjunctiva - with conjunctivitis).
Another common cause of eosinophilia (especially among children) is helminth infestation. Eosinophilia in this case is due to two pathogenetic mechanisms. Firstly, eosinophils have antiparasitic activity - they secrete eosinophilic cationic protein and reactive oxygen species, which are detrimental to helminths. Secondly, the products of helminth metabolism can induce hypersensitivity reactions. That is why helminthic invasions are often accompanied by allergic symptoms.
The most common helminthiases associated with high eosinophilia among children are ascariasis, toxocariasis, among adults - hookworm, opisthorchiasis. In strongyloidiasis, eosinophilic leukocytosis may be the only manifestation for a long time. Eosinophilia is detected as early as 4-5 days of infection. Then it increases very quickly and reaches a maximum by about 30-4 days, and then slowly begins to decrease, but continues to remain at high numbers for a long time. The level of eosinophils is very high (can range from 20% to 70-80%). A sharp increase in eosinophilia occurs during the stage of larval migration through the body and penetration into tissues.
There is a group of lung diseases called pulmonary eosinophilia, which combines a high content of eosinophils in the blood, in the bronchoalveolar fluid and the formation of eosinophilic infiltrates in the lung tissue. The exact pathogenesis of peripheral blood eosinophilia and eosinophil infiltration of lung tissue in most of these diseases is unknown. The following pulmonary eosinophilias are distinguished:
Eosinophilia can occur with lung disease
During some malignant hematological diseases, an increased level of eosinophils with a different pathogenetic mechanism is observed in the blood. In myeloproliferative pathologies (acute and chronic eosinophilic leukemia, chronic myeloid leukemia), aggressive systemic mastocytosis, eosinophilia is caused by tumor (clonal) proliferation of an eosinophilic hematopoietic germ.
Eosinophilia increases slowly over several years. With mastocytosis, it reaches moderate values, with leukemia - pronounced (up to 60-70%). Decreases very slowly, under the influence of chemotherapy. In addition to peripheral blood, eosinophilia is also observed in the myelogram (smear of bone marrow punctate). For leukemia, there is a specific laboratory sign - a simultaneous increase in eosinophils and basophils (basophilic-eosinophilic association).
With lymphogranulomatosis and non-Hodgkin's lymphomas, eosinophilia occurs due to the production of cytokines by lymphatic cells (including interleukin-5), which stimulate the proliferation of normal eosinophils. Eosinophilic leukocytosis is moderate, slowly increasing.
Eosinophilia accompanies some diseases of the digestive system. These include eosinophilic esophagitis, gastritis and enterocolitis. The morphological substrate is the infiltration of the walls of the esophagus, stomach, and intestines by eosinophils. The pathogenesis is still a matter of debate.
It is assumed that in hereditarily predisposed individuals, exposure to food allergens on the mucous membrane causes the activation of antigen-presenting cells (T-lymphocytes) that produce interleukins and eotaxin-3. As a result, eosinophils migrate and infiltrate the mucous membrane of the digestive tract. Eosinophilic leukocytosis is usually mild and occurs only during a severe exacerbation of the disease. A high concentration of eosinophils in the mucosal biopsy, on the contrary, occurs constantly.
Some hormones, such as glucocorticosteroids (hormones of the adrenal cortex), stimulate apoptosis (programmed cell death) of eosinophils. Therefore, diseases accompanied by a decrease in the level of glucocorticosteroids are accompanied by eosinophilia. These pathologies include primary adrenal insufficiency (Addison's disease), congenital dysfunction of the adrenal cortex, as well as multiple endocrinopathies, such as Schmidt's syndrome, panhypopituitarism. The degree of eosinophilia is mild. The number of eosinophils quickly normalizes after the introduction of glucocorticoids.
Eosinophilia occurs in the so-called primary immunodeficiencies - severe diseases with high mortality due to a genetic defect in one or more components of the immune system (cellular, humoral reactions, phagocytosis, etc.). Such diseases are Wiskott-Aldrich syndrome and Job's syndrome (hyper-IgE syndrome). Eosinophilia is probably associated with abnormal overproduction of immunoglobulin E. The level of eosinophils in tissues and blood is very high (up to 60%) and cannot be corrected.
Some tumors, especially adenocarcinomas of the lungs, organs of the digestive and genitourinary systems, have the ability to produce an eosinophilic chemotactic factor that stimulates bone marrow production of eosinophils. With such diseases, eosinophilic leukocytosis increases slowly, reaches high values (up to 20-40%). The concentration of peripheral blood eosinophils returns to normal after long-term chemotherapy or surgical removal of the malignancy.
Eosinophilia is detected by counting the leukocyte formula of a clinical blood test. Since the range of pathologies accompanied by eosinophilia is quite wide, with the first detected changes in the analyzes, it is necessary to consult a general practitioner. To confirm the disease that caused eosinophilia, taking into account clinical and anamnestic data, an examination is prescribed, which may include:
Eosinophilia on a peripheral blood smear
Self-correction of eosinophilia is not possible. To normalize the level of eosinophils, it is necessary to fight the cause. If eosinophilia is mild, associated with the use of drugs or vaccination, or occurs during the period of convalescence, then there is no need to worry. It is necessary to observe the blood dynamics in 7-1 days. If persistent or high eosinophilia is detected in a blood test, you should contact a specialist so that, based on the examination, complaints, anamnesis, he conducts a diagnostic search for the etiological factor and prescribes the appropriate treatment. For the treatment of most diseases accompanied by eosinophilia, drugs from the group of antihistamines or glucocorticosteroids are used.
Only by eosinophilic leukocytosis in the blood alone it is impossible to predict the risk of certain consequences for human health and life. The prognosis is always determined by the underlying disease and the timeliness of its diagnosis - it can vary from favorable in allergic conjunctivitis to a high probability of death in malignant neoplasms or myeloproliferative pathologies. Therefore, any excess of the reference values of eosinophils in a clinical blood test requires a thorough examination to determine the cause.