EOSINOPHILS: CHARACTERISTICS, MORPHOLOGY, FUNCTIONS, DISEASES - GEOGRAFÍA - 2025

An eosinophil is a small and sparse cell of the granulocyte type. They are cells associated with responses to allergies and infections caused by parasites. When cells are stained with eosin, they respond by staining bright red, thanks to the presence of large granules.

Within leukocytes, eosinophils only represent a small percentage of the total number, and their number increases in people with medical conditions such as fever, asthma, or the presence of parasites.

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They are cells with an average diameter of 12 μm and within their morphology the presence of a nucleus composed of two lobes stands out.

These cells can perform phagocytosis, engulfing foreign or foreign particles to the body. In the case of parasites, these are usually larger than the eosinophil, so swallowing it is difficult. Cells can anchor to the surface of the parasite and begin to produce toxic materials.

In general, its main attack mode is by generating toxic compounds on the surface of its targets, such as nitric oxide and enzymes with cytotoxic capacities. These are found inside its granules, and are released during the attack by the parasite or during allergies.

Discovery

The first person to point out the existence of eosinophils was the researcher Paul Ehrlich in the year 1879.

During his research, Ehrlich noticed how a subtype of blood leukocyte reacted avidly to the acid dye eosin, naming this new blood component eosinophils. Later, they were able to identify the enzymes that exist within the granules of the cell.

characteristics

Within the granulocytic cells or granulocytes (cells that have granules inside) we find three types: neutrophils, basophils and eosinophils, which are distinguished from each other by their general morphology and by their response to staining.

Proportionally, neutrophils are very abundant, constituting 50 to 70% of the white blood cells found in circulation, while eosinophils only represent 1 to 3% of these cells.

As with other circulating leukocytes, eosinophils differentiate starting from CD34 ⁺ progenitor cells in the bone marrow. Its formation is induced by a variety of transcription factors and by cytokines. From stem cells, the myeloid cell lineage allows myeloblasts to develop and then they separate into eosinophils.

Eosinophils are cells capable of movement and of phagocytosis. These can move from the blood into the tissue spaces. Although their phagocytic response appears to be overshadowed by neutrophils, eosinophils are involved in defense against parasites and in response to allergies.

In this context, the eosinophil secretes the content of its eosinophilic granules, which manage to damage the membranes of the foreign agent.

Morphology

Eusinophils get their name from the presence of refringent granules of significant size in the cytoplasm of the cell. These granules stain bright red when eosin red acid stain, a normal constituent of Romanowsky and Giemsa stains, is applied.

Dimensions

Its size is between 12 - 17 µm in diameter, comparable (or slightly larger) to that of a neutrophil and approximately 3 times the size of an erythrocyte (red blood cells).

Core

The nucleus has two visible lobes. The chromatin of all nuclei is mainly classified into two types: euchromatin and heterochromatin. The former generally has active and slightly compacted transcription. Heterochromatin, for its part, is compact and is not active in transcription.

In eusinophils, heterochromatin is located mostly near the nuclear envelope, while euchromatin is located more in the center of the nucleus.

Cytoplasm

In the cytoplasm of eosinophils we find the characteristic granules of this cell type. These are classified into two main types: specific granules and azurophilic granules. In the next section we will describe in detail the composition and function of each type of granule.

Eosinophil granules

Specific granules

Specific granules exhibit the crystalloid body, which is surrounded by a less dense matrix. Thanks to the presence of these bodies, the granules have the property of birefringence - the ability to double refraction, splitting a ray of light into two linear and polarized rays.

They are characterized by the presence of four specific proteins: one rich in the arginine amino acid residue called major basic protein (MBP) or main, which is quite abundant and is responsible for acidophilicity of the granule; cationic eosinophil protein (ECP), eosinophil peroxidase (EPO), and eosinophil neurotoxin (EDN).

Only the major basic protein is located in the crystalloid body, while the other typical proteins are dispersed in the matrix of the granule. The aforementioned proteins exhibit toxic properties and are released when infestations by protozoa and parasitic helminths occur.

In addition, they possess phospholipases B and D, histaminase, ribonucleases, B-glucuronidase, cathepsin and collagenase.

Major basic protein (MBP)

MPB is a relatively small protein made up of 117 amino acids, with a molecular weight of 13.8 kD and a high isoelectric point, above 11. The genes that code for this protein are found in two different homologues.

The toxicity of MPB against helminths has been proven. This protein has the ability to increase the permeability of the membrane through ion exchange, resulting in a disruption in the aggregation of lipids.

Cationic Eosinophil Protein (ECP)

ECP is a protein that ranges in size from 16 to 21.4 kD. This range of variation may be influenced by the different levels of glycosylation at which the protein has been found. There are two isoforms of ECP.

It exhibits cytotoxic, helmintotoxic, and ribonuclease activity. In addition, it has been related to the response to the suppression of the proliferation of T cells, synthesis of immunoglobulins by B cells, among others.

Eosinophil peroxidase (EPO)

This enzyme with peroxidase activity is made up of two subunits: a heavy chain of 50 to 57 kD and a light chain of 11 to 15 kD.

The action of this enzyme produces reactive oxygen species, nitrogen-reactive metabolites and other compounds that promote oxidative stress - and consequently apoptosis and necrosis.

Eosinophil neurotoxin (EDN)

This protein has ribonuclease and antiviral activity. EDN has been found to induce dendritic cell maturation and migration. It has also been linked to the adaptive immune system.

Although the four enzymes described have many points in common (in terms of their function), they differ in the way they attack helminth infestations. For example, ECP is almost 10 times more powerful than MBP.

Azurophilic granules

The second type of granule is lysosomes, which contain a range of enzymes of the acid hydrolases type (as is common in organelles) and other hydrolytic enzymes that actively participate in the fight against the pathogen and in the breakdown of antigen-antigen complexes. which phagocytes the eosinophil.

Features

Defense against parasites and response to allergies

Historically, eosinophils have been considered primitive myeloid cells involved in defense against parasites and allergic inflammations. The release of arylsulfatase and histaminase occurs from allergic reactions. Consequently, the eosinophil count is usually elevated in patients with this condition.

Homeostasis and immunoregulation

Currently, research has revealed that this cell also plays a key role in homeostasis and immunoregulation. By performing the genetic treatments necessary to truncate the production of eosinophils in laboratory mice, it was possible to study these eosinophil-deficient rodents.

In these strains of mice, the importance of these granulocyte-like cells was demonstrated in several fundamental processes, such as the production of antibodies, glucose homeostasis and the regeneration of some tissues, such as muscle and liver.

Today, it has been established that the role of eosinophils in humans encompasses broader aspects than responding to allergies and infestations. Among them are:

Cytokine synthesis

Eosinophils have the ability to synthesize a series of cytokines, which are molecules that regulate cellular functions and are involved in communication. Cytokine production by these cells occurs in small amounts.

Role in reproduction

The uterus in an area rich in eosinophils. The evidence suggests that these cells could be involved in the maturation of the uterus and in the development of the mammary glands.

Normal values ​​and associated diseases

Although it can vary between laboratories, it is considered that a healthy person should have a percentage of eosinophils in the blood in the range of 0.0 to 6%. The absolute count should be between 350 to 500 per mm ³ of blood. This means that in healthy individuals the count is not greater than 500.

Normal variations in eosinophil count

The eosinophil count is higher in newborns and infants. As you get older, the number of these cells decreases. Pregnant women are also characterized by a low eosinophil count.

In addition, most eosinophils tend to reside in areas where there are mucous membranes. They are very abundant in the connective tissue located in the proximity of the lining of the intestine, the respiratory tract and the urogenital tract.

Physiologically, eosinophil values ​​vary in peripheral blood throughout the day, the highest value of these cells corresponding to the early hours of the morning where steroid peaks are at their lowest.

Eosinophilia: high eosinophil values

If the patient's count exceeds 500 eosinophils, it is indicative of some pathology and requires further medical analysis. This abnormal count is known in the literature as eosinophilia. The condition usually lacks symptoms.

There are different degrees of eosinophilia, depending on the number of eosinophils found in the sample. It is said to be mild if the count is between 500 and 1500 mm ³, moderate if the count is between 1500 and 5000 mm ³. In the event that the count exceeds 5000 mm ^3, eosinophilia is severe.

If symptoms do occur, they will depend on the area where the alarming levels of eosinophils are found, whether in the lungs, heart, stomach, among other organs.

Children are more likely to present this condition and to acquire multiple infections by parasites - due to their childlike behavior, such as playing on the floor, having direct contact with pets without the necessary hygiene, among other factors.

Hypereosinophilic syndrome

When the eosinophil count is particularly high and no immediate cause is found, call it parasite infestation or allergies, the patient has hypereosinophilic syndrome. This condition is rare and usually appears in male patients over 50 years of age.

The increase in eosinophils without associated parasitosis usually causes damage to some organs, usually the heart, nervous system, and lungs. Severe damage occurs if the hypereosinophilic condition is persistent.

There are two types of the disease: the myeloprofilerative one that is associated with the loss of a DNA segment on chromosome four and the lymphoproliferative variant is associated with an aberrant phenotype of T lymphocytes.

To restore normal values ​​of these cells, your doctor may prescribe certain medications - imatinib is one of the most common.

Low eosinophil values

Low eosinophil count is related to Cushing's syndrome, a medical condition associated with high cortisol values, and is characterized by weight gain in patience thanks to the disproportionate distribution of fat in the body.

Other causes that can decrease the number of eosinophils are infections in the blood and taking steroids. When the doctor optimally addresses these conditions, the number of eosinophils is restored.

A low eosinophil count is not usually very alarming, since other cells of the immune system can compensate for their work.

References

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