Year : 2003 | Volume
: 7 | Issue : 2 | Page : 31--33
Eosinophils in health and disease: An overview
TR Saraswathi, S Nalinkumar, K Ranganathan, R Umadevi, Joshua Elizabeth
Department of Oral Pathology. Ragas Dental College and Hospital, Chennai, India
Department of OP, Ragas Dental College and Hospital 21102, East coast road Uthandi, Chennai 119
Eosinophils are granulocytes, which are present in a variety of diseases. They perform numerous important functions and play a key role in defense against various diseases. The structure, contents of granules, functions, activation, emigration, infiltration and degranulation of eosinophils are discussed in this article. Eosinophilia and associated oral diseases are also mentioned.
|How to cite this article:|
Saraswathi T R, Nalinkumar S, Ranganathan K, Umadevi R, Elizabeth J. Eosinophils in health and disease: An overview.J Oral Maxillofac Pathol 2003;7:31-33
|How to cite this URL:|
Saraswathi T R, Nalinkumar S, Ranganathan K, Umadevi R, Elizabeth J. Eosinophils in health and disease: An overview. J Oral Maxillofac Pathol [serial online] 2003 [cited 2020 Feb 29 ];7:31-33
Available from: http://www.jomfp.in/text.asp?2003/7/2/31/40933
Eosinophils are bone marrow derived granulocytes and are found in abundance in hypersensitivity reactions and parasitic infections  . They were discovered by Paul Ehrlich in 1879. They can be distinguished from othergranulocytes by the affinity of their cytoplasmic granules for acidic stains like eosin; resulting in intense red staining, which gives them their name  .
Hematopoiesis or generation of blood cells occurs in the bone marrow in adults. All the blood cells originate from a common stem cell, which becomes committed to differentiate along particular lineages. This pluripotent stem cell broadly differentiates into a myeloid progenitor cell or a lymphoid progenitor cell. The lymphoid progenitor cell gives rise to the lymphocytes, whereas the myeloid progenitor cell differentiates along different lineages namely erythroid, megakaryocytic, granulocytic and monocytic. The myeloid progenitor cell differentiates along one particular lineage called eosinophil colony forming unit (CFIJ-Eo) and forms eosinophils  . Bone marrow generation of eosinophils is regulated by interleukin-5 and the release from the circulation into the tissues requires the action of several chcmokines, cytokines and adhesion molecules 
Structure of eosinophils
Eosinophils comprise about 1-3% of white blood cells in the blood. The normal range of eosinophils is 40-450 cells/cu. mm. The diameter of an cosinophil is 10-12 microns. The eosinophil is characterized by its abundant cytoplasm with coarse reflective granules, which stain red  . These granules appear as rod like crystalloid inclusions when viewed by electron microscope. The nucleus is in the shape of two lobes connected by a bridge.
Contents of eosinophil granules
The eosinophil has many proinflammatory mediators with considerable potential to initiate and sustain an inflammatory response. These include cylotoxic granule proteins, cytokines, chemokines, and lipid mediators  . The proteins present in the eosinophil granules include Major Basic Protein (MBP), Eosinophil Cationic Protein (ECP), Eosinophil Derived Neurotoxin (EDN), Eosinophil Peroxidase (EPO), aryl sulfatase and hydrolytic enzymes ,, .
Functions of eosinophils
Eosinophils play a protective role in host immunity to infections by parasitic worms and are involved in the pathophysiology of asthma and other allergic diseases , . The cytoplasmic granules are toxic to parasitic worms and limit the extent of worm infestations  . Eosinophils mediate a special type of Antibody Directed Complement Cytotoxicily (ADCC) against some helminthic parasites  , Eosinophils also contain histaminase that may modulate mast cell mediated inflammation  and collagenase, which may aid in remodelling connective tissue during healing. Eosinophils are also involved in the killing of bacteria through eosinophilic peroxidase activity (3). Synthesis and expression of class II proteins of the major histocompatibility complex (MIIC) may enable eosinophils to serve as antigen-presenting cells 
Eosinophil activation involves chemotactic factors for eosinophils, namely worm extracts, histamine and eosinophilic chemotactic factor A in mast cells. neutrophil peptides, eosinophil stimulator & promoter substances in lymphocytes, C5a complement and eotaxin. Eotaxin is a novel eosinophil-selective chemoattractant, that plays a major role in eosinophil recruitment in allergic inflammation and parasitic diseases  .
There are many methods of eosinophil activation. Eosinophils are activated by phosphorylation of signal transducing proteins within the eosinophils, which will lead to release of granules by exocytosis. Activated eosinophils produce Platelet Activating Factor (PAF), which acts as an autocrine substance to increase the activated state of eosinophils. PAF is also produced by endothelial cells that will result in further activation of eosinophils. In addition, eosinophils also have receptors for IgA that can he activated as a result of cross-linking by antigens. Chemokines such as Regulated and Normal T-lymphocyte Expressed and Secreted (RANTES), cotaxin and Major Inflammatory Protein (MIP-1) are considered to be involved in the pathophysiology of allergic inflammation because of their ability to drive eosinophils through their binding sites, expressed on eosinophils  .
The recruitment of eosinophils to sites of allergic inflammation is a complex process that is mediated by inflammatory cytokines and chcmokines  . These molecules act to stimulate peripheral eosinophilia, and regulate homing of eosinophils to the inflamed site. They also promote eosinophil-vascular endotheliurn interactions, extravasation, chemotaxis, and localization to the site of the inflammatory stimulus . Lymphocytes release cytokines, which recruit and activate eosinophils. These cytokines also generate adhesion molecules on endothelial cell surfaces that promote diapedesis of the eosinophils out of the circulation into the tissues. In the tissues, the eosinophils degranulate, releasing toxic proteins and thus perform their functions , .
Helminthes are too large to be engulfed by phagocytes. IgE coats these helminthes. Once eosinophils have emigrated into the tissues, they bind with this IgE. This is followed by degranulation of the eosinophils leading to the release of the toxic granules. MBP and I. CP present in the granules are responsible for the killing of the parasites  .
Degranulation of eosinophils in target tissues is considered a key pathogenic event in major chronic eosinophilic diseases  . Biopsy specimens tram patients with inflammatory bowel disease, allergic rhinitis, asthma, and nasal polyposis when evaluated with transmission electron microscopy display a similar degree of local tissue eosinophilia. In contrast, marked differences in the mean extent of eosinophil degranulation were observed between the patient groups. Different eosinophilic conditions, despite having similar number of tissue eosinophils, may exhibit markedly different degranulation patterns  .
Eosinophilia is defined as an increase in the number of eosinophils above 450/cu.mm It is not the actual disease process but the response to a disease. Eosinophilia is seen in allergic disorders like asthma, eczema, urticaria, angioneurotic edema, and drug sensitivity  . It is commonly present in parasitic infestations and skin disorders like pemphigus, bullous pemphigoid, erythema multiforme, Kimura's disease and angiolymphoid hyperplasia , . Diseases of haematopoietic system like chronic myeloid leukemia, polycythemia vera, pernicious anaemia, myelofibrosis, and Hodgkin's lymphoma  also may exhibit eosinophilia. Eosinophilia is present in collagen vascular diseases like rheumatoid arthritis, periarteritis and systemic lupus erythematosus  . Eosinophilia can be present in malignant disease of any type especially with metastasis. Miscellaneous causes of eosinophilia include X-ray irradiation, sarcoidosis, eosinophiliamyalgia syndrome and hypereosinophilia syndrome  .
Eosinophils and oral diseases
In the head and neck region, eosinophilia is present in many diseases Eosinophilia is seen in reactive lesions of the oral cavity like allergic gingivitis and lichenoid mucositis. Lichenoid mucositis are lesions that are clinically identical to lichen planes occurring bilaterally or unilaterally. Histopathologically, it differs from lichen planes in that, the subepithelial lymphocytic infiltrate lacks the well-defined "band like appearance," being more diffuse and deep. containing eosinophils and plasma cells. Perivascular infiltration is also seen in sonic cases  . Eosinophilia is present in vesiculobullous lesions like pemphigus, erythema multiforme, and the like  . Patients affected with oral fungal lesions present with eosinophilia  . Eosinophilia is frequently seen in patients suffering from parasitic infections like cysticercosis  , hydatid cyst and filariasis  . A rare oral lesion associated with eosinophilia is Traumatic Ulcerated Granuloma with Stromal Eosinophilia (TUGSE) , . Kimura's disease  and Langerhans cell histiocytosis  are other diseases that stay manifest in the oral cavity having an association with eosinophils.
Eosinophils are granulocytes, which are present in a variety of diseases. They are multi faceted cells, which perform an array of functions. Eosinophilia is seen in wide spectrum of diseases ranging from simple allergy to malignancy with metastasis. In patients with eosinophilia, it is prudent to have a thorough investigation performed to diagnose and rule out any underlying systemic disease.
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