Eosinophils high

What are Eosinophils ?

Eosinophils are a kind of kind of white blood cells that are manufactured in the bone marrow and later migrate into the blood. The eosinophils consist of approximately one to six percent of the total count of white blood cells in healthy individuals. They can be found circulating in the blood and are also present outside the blood vessels in different tissues and organs of the body. As compared to other organs, the largest percentage or concentration of eosinophils can be typically found in the gastrointestinal tract. In addition to the mast cells, the eosinophils also play a role in the regulation of mechanisms related to asthma and allergies.

Eosinophils defend the body by killing parasites, bacteria and other microorganisms. However, they can also cause problems when they incorrectly and mistakenly react, leading to the development of inflammatory reactions and other allergies in the body. For example, the presence of food allergies can result in the collection of excessive number of eosinophils in the digestive tract, eventually causing different symptoms ranging from diarrhea to destruction of the cells that line the gastrointestinal tract.

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Eosinophils are considered to be a constituent of the innate immune system, which signifies that they have the ability to ‘non-specifically’ destroy any foreign bodies that they may come across in the body, like parasites and bacteria. Here, the term ‘non-specifically’ indicates that eosinophils do not need distinguish a particular invader exclusively, but can instead simply determine the attacker as something that need not occur in the body and hence has to be destroyed.

Eosinophils are generally around 12 to 17 micrometers in size. They can be observed to be present in the junction between the medulla of the thymus and the cortex, the medulla, ovary, the lower GI tract, spleen, uterus and spleen. However, in normal conditions, eosinophils may not be found in the esophagus skin, and lungs. When eosinophils are found to occur in these organs then it signifies that there may be an underlying disease causing it.

Eosinophils can be found in the circulatory system for eight to twelve hours and can live for an extra eight to twelve days, when there is no stimulation. The initial work conducted on eosinophils in the early eighties suggested that they were distinct granulocytes, which had the ability to live for prolonged durations post maturation. The various ex-vivo culture experiments demonstrated this observation.

Eosinophils Function

Once the eosinophils are stimulated and activated, they perform the function of:

  • Producing cationic granule proteins  which are then released via degranulation
  • Producing lipid mediators such as the eicosanoids from the prostaglandin (like PGE2) and leukotriene (like LTE4 and LTC4) families
  • Producing cytokines like IL-1, IL-4, IL-2, IL-5, IL-8, IL-6, TNF alpha and IL-13
  • Producing reactive oxygen species like peroxide, superoxide, and hypobromite, which is hypobromous acid, that is manufactured preferentially by eosinophil peroxidase
  • Producing different growth factors like VEGF, TGF beta, and PDGF
  • Producing various enzymes, like elastase, etc.


  • Eosinophils have a vital role to play in defending the body against viral infections. This can be identified from the fact that large quantities of RNases can be found to be present inside their granules.
  • They are responsible for fibrin elimination at the time of inflammation
  • Recent studies have indicated that eosinophils play a role in antigen presentation to T cells
  • Eosinophils in association with mast cells and basophils are vital mediators of asthma pathogenesis and allergic responses, and are also related to the severity of the disease.
  • They efficiently tackle helminth or worm colonization and the levels of eosinophils may be somewhat elevated when certain parasites are present
  • They are involved in a number of biological process, which include oestrus cycling, mammary gland development post puberty, neoplasia and allograft rejection.

Eosinophils Normal Range

The Normal range in adults is 0 – 5 and an optimal adult reading should be 2.5

Eosinophils High and Low

Anything above 5 percent is considered high and can denote allergies. A low Eosinophils count  is not a problem and is found mostly due to administration of steroids.  Secondly, it is not considered because the reference range of normal eosinophils range starts from 0

Eosinophilia –  Causes

When eosinophils present in the blood increase substantially and measure more than 500 eosinophils/microlitre of blood, then the resultant condition is referred to as eosinophilia.

The condition can be generally observed in individuals who have:

  • An infection of the intestines by parasites
  • Addison’s disease
  • Malignant diseases like the Hodgkin’s disease,
  • A collagen vascular disorder such as rheumatoid arthritis
  • Widespread skin diseases like exfoliative dermatitis, etc.

It can also occur due to intake of certain drugs like penicillin or can be found in the squamous epithelium section of the esophagus, during conditions like eosinophilic esophagitis and reflux esophagitis

It may be noted that in the year 1989, use of contaminated L-tryptophan supplements resulted in a dangerous type of eosinophilia called eosinophilia-myalgia syndrome, which was similar to the Toxic Oil Syndrome that occurred in Spain in the year 1981

Treatment for Eosinophilia

Some of the treatment methods used to overcome autoimmune disorders and diseases caused due to eosinophils are as follows:

  • Monoclonal antibody therapy. For example, reslizumab or mepoluzimab against IL-5, can prevent eosinophilopoiesis
  • Corticosteroids. It promotes apoptosis and the eosinophils count in blood are quickly reduced
  • Gleevec (STI571) which restrains PDGF-BB in hypereosinophilic leukemia
  • Antagonists of receptors or leukotriene synthesis


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