Eosinophil and Eosinophilic Pneumonia
PKGhatak, MD
Eosinophils are white blood cells (WBCs), belong to cellular immunity and are called immunocytes. Eosinophils are strikingly different from the other WBCs.
The cytoplasm of the eosinophil contains many granules, stained red or pink with an acidic dye, Eosin. The name eosinophil means - love eosin. The nucleus of the cell is bi-lobed. The granules contain preformed enzymes, lysosomes, cytokines, prostaglandins, thromboxane. The cells also supply NO, O, H2O2, and OH groups. Cells exhibit amoeboid movement and phagocytic activities. The surface of cells contains various receptors namely cytokine receptors, active receptors, lipid mediated receptors, pattern recognition receptors, FC fraction immunoglobulin receptors, and adhesion receptors.
In health, the eosinophils are present in the thymus gland, spleen, lymph nodes, entire GI tract with the sole exception of the esophagus, and in the bone marrow and peripheral blood. Eosinophils migrate to tissues when summoned by Interleukin IL-3 and IL-5. They move out of blood vessels by Brownian movement and attach to cells and tissue by adhesion receptors and then release stored chemicals. The chemical paralyzes parasites, stimulates phagocytosis by macrophages, may produce damage to tissues, and participate in inflammation, repair and remodeling and regeneration of organs/ tissues.
In the peripheral blood, the eosinophils count is 2 to 8 % of the total WBC. The actual number is between 500 to 800 per mcL. The life span of eosinophil in the peripheral blood is 2 to 4 days and in the tissues 14 days or longer by the action of interleukin.
Eosinophils produce airway constriction by histamine release from mast cells, increase mucus secretion from goblet cells, and promote the proliferation of intercellular matrix by TGFB.
When the eosinophil count increases over 800 /mcL the condition is known as eosinophilia. In chronic eosinophilic syndrome, the count is over 1,500 /mcL. In chronic eosinophilic leukemia, the count is over 100, 000 /mcL.
Eosinophils are very active in parasitic infestation, allergy, asthma, drug induced allergy, and cancers. There are some special diseases that arise from eosinophil dysfunctions and one of them is Acute eosinophilic pneumonia.
Acute Eosinophilic Pneumonia:
Acute eosinophilic pneumonia is a rare disease but a serious illness. The illness develops most frequently in young males in 20 to 35 yrs. of age who are trying to start smoking cigarettes for the first time or have taken up smoking again after a brief period of quitting. Pneumonia once starts rapidly spreads to both lungs and in 4 to 7 days becomes quite extensive. The distinctive features of this rapidly spreading pneumonia are progressive shortness of breath and quick onset of respiratory failure. Blood count shows no increase in eosinophil count.
The pathological picture is of interstitial pneumonia with extensive infiltration of eosinophils. Other features are rapid loss of weight, night sweats, cough and fever.
The cause of the illness is unknown. Various theories are advanced but none are convincing. And no hereditary predisposition is known.
Clinical signs are typical interstitial pneumonia. Diagnosis is based solely on finding a large percentage of eosinophils in the bronchial lavage fluid obtained at the time of bronchoscopy, and/or demonstrating massive eosinophil infiltration of lung parenchyma in the biopsy specimens.
Treatment.
A marked drop in O2 saturation may develop at any time, so monitoring of patients in the ICU is essential and prompt correction of O2 deficiency is needed. Respiratory failure is treated with non-invasive ventilation or intubation and mechanical ventilation. High dose IV steroid shows quick response; 3 to 5 days later IV steroid is switched to the oral route and gradually completely withdrawn. Once recovered from an acute illness there is no recurrence of pneumonia and the prognosis is excellent.
Acute eosinophilic pneumonia requires to be differentiated from Chronic eosinophilic pneumonia, Churg-Strauss syndrome, Loffler's syndrome and Tropical pulmonary eosinophilia.
Chronic eosinophilic pneumonia is not a disease of the young, the peak incidence is in the 5th decade and both sexes are equally affected. It is chronic and recurrent in nature and often accompanies asthma. Pneumonia does not lead to respiratory failure. Blood count shows high eosinophils in the peripheral blood in contrast to acute eosinophilic pneumonia.
Churg-Struss syndrome is a multisystem eosinophilic vasculitis with granuloma formation. Asthma is often an underlying condition, and blood eosinophil count is high. 50% of cases show the presence of c-ANCA (ANCA= antineutrophilic cytoplasmic antibody).
Loffler's syndrome is recurrent asthmatic episodes due to infiltration of the lungs by eosinophils resulting from larval migration through the lungs. The larvae are Ascaris lumbricoides and also larvae of other parasites. Blood eosinophil count is high.
Tropical eosinophilia is a prevalent disease in coastal areas in India and the Indian subcontinent. Eosinophil count is generally over 3,000 /mcL, serum IgE levels over 1,000 units and a positive filaria antigen test. Symptoms of wheezing, cough and asthma like attacks coincide with the periodic release of microfilaria into the blood by adult filaria worms residing in lymph nodes. The pathological picture varies according to the duration of the disease from simple pulmonary eosinophil infiltrates to pulmonary fibrosis.
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