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

From a clinical point of view, knowledge of the different components of blood and their concentrations is of paramount importance. From red blood cells to white blood cells, platelets and hemoglobin, every substance carried in the blood has an essential function for the body.

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

For all these reasons, we see that it is particularly interesting to delve into the world of leukocytes. Inside our body we have a veritable legion of protectors, and today we tell you all about each of them.

    Leukocytes: protective cells for life

    From a terminological point of view, a leukocyte or a white blood cell is defined as a type of blood cell (blood cell) that occurs in the bone marrow and is found in the blood and lymphatic tissue. These cell bodies form the human immune system along with many other barriers (such as mucous membranes or skin, for example), and as a whole seek the permanence of the individual over time for as long as possible.

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

    1. Granulocytes

    They are the most common type of white blood cell, Representing 70 to 75% of this protective cell conglomerate. Depending on the type of staining that allows its identification in the patient’s blood sample, the different types of granulocytes can be differentiated.

    1.1 Neutrophils

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

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

    neutrophils they kill 3 to 20 bacteria in their lifetime. Attracted by toxic compounds synthesized by the pathogen, these white blood cells end the threat by phagocytosis and the 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 the basophils, so these are the least common white blood cells, accounting for 0.5 to 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 their permanence in the blood is a few hours. They are around 12-15 microns in size (the largest leukocytes), have a bilobed nucleus, and are stained with basic dyes.

    These agents have an active immune responseAs they have specific granules that release histamine, heparin, bradykinin, serotonin and other compounds that are involved in inflammatory responses. They are an essential cell body in allergic responses.

    1.3 Eosinophils

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

    Despite a blood half-life of 3 to 4 days, the highest concentration of eosinophils is found in the tissues, Since the existence of 100 tissue eosinophils for each in circulation has been established. Its main function is the detection and phagocytosis of larvae and parasites, as well as the modulation of the allergic response, since they prevent the exacerbation of these by synthesizing substances that neutralize basophils.

      2. Agranulocytes

      On the other hand, we have the agranulocytes, which, as the name suggests, are cells devoid of mononuclear granules. We briefly mention both 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 they are more common in the lymphatic system than in blood plasma and can be divided into two types according to their origin and functionality: B and T.

      Although perhaps sinful for reductionists, we can summarize the general function of lymphocytes in the following concept: B lymphocytes would become the “body recognition system” because they unequivocally detect pathogens and immobilize them. On the other hand, T lymphocytes are the “labor force” because their lytic activity neutralizes the pathogenicity of cells infected with microorganisms.

      2.2 Monocytes

      At the last stop of this trip we have to monocytes, the largest leukocytes (18 micrometers) which represent 2 to 8% of white blood cells. Their formation process in the bone marrow takes two to three days, but they do not stay in the blood for more than 36 hours, as they quickly migrate to infected tissue.

      Its function is basic: they phagocytose pathogens, that is, they are literally eaten. It is estimated that a monocyte can ingest up to 100 bacteria in its lifetime, so they are considered the white blood cells with the highest bactericidal capacity on the entire list.

      Functions of white blood cells

      Without realizing it, in the above classification we have described all the essential functions of leukocytes. Either way, a general exam never goes badly. As we said in the previous lines, white blood cells are responsible for promoting inflammatory responses, phagocytation of pathogens, their recognition and isolation, among many other functions.

      It’s all part of the innate and acquired immune response, an excellent defense mechanism that allows us to thrive in an environment filled with potentially harmful microorganisms.

      Problems in defense barriers

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

      • Neutropenia: There are a number of conditions that can lead to low white blood cells. In this case, the most affected are usually the neutrophils.
      • Lymphocytopenia: It is defined as a total number of lymphocytes less than 1.0×109 / L. Factors such as radiation therapy or chemotherapy can promote this condition.
      • Neutrophilia: excess neutrophils in the circulating blood. It can be caused by infections with serious illnesses such as leukemia.
      • Eosinophilia: When the presence of eosinophils is greater than 0.65 × 109 / L. It is usually caused by infectious processes.

      It should be noted that we are not dealing with a disease per se, but it is a sign of an underlying problem. Sporadic neutrophilia events, for example, are relatively normal, because in the face of an inflammatory process or infection, it is natural that these cells proliferate more.

      Of course, abnormal leukocyte values they can respond to a number of very diverse pathologies: From infections and genetic diseases, to bone marrow disorders, cancerous processes, surgeries and many other events, an erroneous white blood cell count continues to sound the alarm bells.


      As we have been able to observe, leukocytes come in different shapes, sizes and colors. In addition to this, each of them performs a unique and irreplaceable function with regard to the immune system, therefore from inflammation to phagocytosis, these motive agents fiercely fight the pathogens that enter our body.

      Of course, it is impressive to know that our body is able to develop such an efficient and refined defense system. The key to evolution lies in refinement and it applies far beyond the immune system, and for this reason we will never cease to be surprised to describe and discover processes like these.

      Bibliographical references:

      • Abbas, AK, Lichtman, AH and Pillai, S. (2015). Cellular and molecular immunology. Elsevier.
      • Arevalo, M., Arredondo, S., Walter, T., and Heresi, G. (1986). Techniques for evaluating the phagocytic, opsonic and bactericidal capacity of polymorphonuclear leukocytes. Tower. chil. tecnol. medium, 383-388.
      • Definition of white blood cells, cancer.gov. Retrieved October 16, from https://www.cancer.gov/espanol/publicaciones/diccionario/def/leucocito.
      • Leukocyte Formula, Medlineplus.gov. Retrieved October 16, from https://medlineplus.gov/spanish/pruebas-de-laboratorio/formula-leucocitaria/.
      • Point 23: white blood cells. Efervescente.com. Collected October 16 at http://www.enfervescente.com/privado/wp-content/uploads/2013/02/Tema-23.-Gl%C3%B3bulos-blancos-o-leucocitos.pdf.

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