Leukocytes: what are they, types and functions in the human body

From a clinical point of view, knowing the different components of the blood and their concentrations is of essential importance. From red blood cells, through leukocytes, platelets or hemoglobin, every substance carried in the blood has an essential function for the body.

In addition to this, knowledge of leukocytes at the evolutionary level should not be underestimated. The immune system of living beings allows us to develop in space and time over the years, since If we did not have such effective defense methods against pathogens, our existence would be much shorter and hard.

For all these reasons, we are especially interested in immersing ourselves in the world of leukocytes. Inside our body we have a true legion of protectors, and today we tell you everything about each one of them.

Related article: "Major Cell Types of the Human Body"

Leukocytes: Protective Cells of Life

From a terminological point of view, a leukocyte or white blood cell is defined as a type of blood cell (blood cell) that is made in the bone marrow and is found in the blood and lymphatic tissue

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. These cell bodies form the human immune system along with many other barriers (such as mucous membranes or the skin, for example), and as a whole, they seek the permanence of the individual in time for the maximum possible period.

Without further ado, and since we have a lot of fabric to cut, we present below the types of leukocytes and their characteristics.

1. Granulocytes

They are the most common type of white blood cell in the blood, representing 70-75% of this protective cell conglomerate. Depending on the type of stain that allows its identification in the patient's blood sample, we can differentiate different types of granulocytes.

1.1 Neutrophils

Within the group of granulocytes, neutrophils are the most common cells, since represent 60-70% of leukocytes in humans. As morphological characteristics, we can note that they measure from 9 to 12 micrometers and that the granules of their cytoplasm are stained light purple with neutral dyes (hence their name).

They mature in the bone marrow and are stored in it before being sent to the bloodstream, a process that lasts a total of 10 days. After this, they travel through the blood vessels and through small pores (diapédesis) are able to enter the tissues affected by pathogens. These agents remain in the blood for about 8-20 hours, but their half-life is increased by several magnitudes when they enter infected or inflamed tissues.

Neutrophils kill 3 to 20 bacteria in their lifetime. Attracted by the toxic compounds synthesized by the pathogen, these white blood cells kill the threat through phagocytosis and release of hydrolytic enzymes. In addition to this, they also promote the local inflammatory process typical of an infection.

1.2 Basophils

On the other side of the coin we have basophils, since are the least common white blood cells, representing 0.5-1% of the total. They are also more "ethereal" than their previously described companions, as they mature in the bone marrow in a total of three days and stay in the blood for a few hours. They measure about 12-15 microns (they are the largest leukocytes), have a bilobed nucleus, and are stained with basic dyes.

These agents have an active response at the immune level, as they have specific granules that release histamine, heparin, bradykinin, serotonin, and other compounds that mediate inflammatory responses. They are an essential cell body in allergic responses.

1.3 Eosinophils

The last within the group of granulocytes, but no less important. Eosinophils are present in a proportion of 2-4% of all white blood cells. Their size is similar to that of a neutrophil, and they are stained orange by acid dyes (eosin).

Despite having a blood half-life of 3 to 4 days, the highest concentration of eosinophils is found within tissues, since the existence of 100 tissue eosinophils for each circulating one has been verified. Its main function is the detection and phagocytosis of larvae and parasites, in addition to modulating the allergic response, since they prevent the exacerbation of it by synthesizing substances that counteract the basophils.

You may be interested in: "Erythrocytes (red blood cells): characteristics and function"

2. Agranulocytes

On the other hand we have agranulocytes, which, as their name indicates, are cells lacking granules of mononuclear nature. We briefly mention the two types within this group.

2.1 Lymphocytes

Of course, no summary paragraph can do justice to the complexity and functionality of these cell bodies. Lymphocytes are more common in the lymphatic system than in blood plasma and they can be divided into two types according to their origin and functionality: B and T.

Although we may be being reductionist, we can summarize the general function of lymphocytes in the following concept: B lymphocytes would become the “body recognition system”, since they unequivocally detect pathogens and immobilize. On the other hand, T lymphocytes are the “workforce”, since their lytic activity neutralizes the pathogenicity of cells infected by microorganisms.

2.2 Monocytes

At the last stop on this trip we have monocytes, the largest leukocytes (18 microns) that represent 2-8% of white blood cells. Their formation process in the bone marrow takes two to three days, but they do not remain in the blood for more than 36 hours, since they migrate rapidly to infected tissues.

Its function is basic: they engulf pathogens, that is, they literally eat them. It is estimated that a monocyte can ingest up to 100 bacteria throughout its life, which is why they are considered the white blood cells with the highest bactericidal capacity on the entire list.

White blood cell functions

Without realizing it, in the previous classification we have described all the essential functions of leukocytes. Anyway, a general review never hurts. As we have already said in previous lines, white blood cells They are responsible for promoting inflammatory responses, phagocytizing pathogens and recognizing and isolating them, among many other functions.

All of this is part of both the innate and acquired immune response, an excellent mechanism for defense that allows us to develop in an environment full of potentially microorganisms harmful.

Defense barrier problems

What happens when these essential cells fail? The leukocyte formula is a type of medical test that allows us to measure the concentration of white blood cells in the blood, and depending on the observed imbalances, various pathologies can be recorded. Among them we find the following:

Neutropenia: a number of disorders can cause a decrease in white blood cells. In this case, the most affected are usually the neutrophils.
Lymphocytopenia: It is defined as a total lymphocyte count less than 1.0x109 / L. Factors such as radiation or chemotherapy can promote this state.
Neutrophilia: an excess of neutrophils in the circulating blood. It can be caused from infections to serious diseases like leukemia.
Eosinophilia: when the presence of eosinophils is greater than 0.65 × 109 / L. It is usually caused by infectious processes.

Notably We are not facing a disease in itself, but it is a sign of an underlying problem. Sporadic events of neutrophilia, for example, are relatively normal, since in the face of an inflammatory process or infection, it is natural for these cells to proliferate to a greater extent.

Of course, abnormal white blood cell values can respond to a series of very diverse pathologies: from infections to genetic diseases, through disorders of the bone marrow, processes cancer, surgeries, and many other events, a sustained erroneous white blood cell count should set off the alarms.

Resume

As we have seen, leukocytes come in various shapes, sizes, and stains. In addition to this, each of them performs a unique and irreplaceable function as far as the immune system is concerned, since from the inflammation to phagocytosis, these cellular agents fight tooth and nail the pathogens that enter our Body.

Of course, it is impressive to know that such an effective and refined defense system is capable of developing within our body. The key to evolution lies in refinement and applies far beyond the immune system, and for this reason, we will never cease to be amazed when describing and discovering processes like these.

Bibliographic references:

Abbas, A. K., Lichtman, A. H., & Pillai, S. (2015). Cellular and molecular immunology. Elsevier.
Arévalo, M., Arredondo, S., Walter, T., & Heresi, G. (1986). Techniques to evaluate the phagocytic, opsonic and bactericidal capacity of the polymorphonuclear leukocyte. Rev. chil. technology Med, 383-388.
Definition of white blood cells, cancer.gov. Picked up on October 16 in https://www.cancer.gov/espanol/publicaciones/diccionario/def/leucocito.
Leukocyte Formula, Medlineplus.gov. Picked up on October 16 in https://medlineplus.gov/spanish/pruebas-de-laboratorio/formula-leucocitaria/.
Unit 23: white blood cells. Effervescente.com. Picked up on October 16 in http://www.enfervescente.com/privado/wp-content/uploads/2013/02/Tema-23.-Gl%C3%B3bulos-blancos-o-leucocitos.pdf.