Leukocytes

What are they

Leukocytes are the so-called white blood cells, defined as such as they lack the typical pigmentation, visible under a microscope, which instead characterizes red blood cells (or erythrocytes).

Unlike the latter and other elements circulating in the blood (platelets), leukocytes are also real cells with a nucleus (the cellular organelle that contains most of the genetic material).

The term “leukocytes” indicates the entire population of white blood cells, which includes at least five different cell types, for morphology and function, only among those circulating, in addition to some cell types that differ within the tissues.

From a functional point of view, leukocytes are the protagonists of the immune system, within which the different cell types each play a specific and exclusive role. Although leukocytes together represent only about 1% of circulating blood volume and are numerically much lower than erythrocytes (4,000-11,000 per cubic millimeter compared to 4-6 million), on them the complex network of the body’s defense mechanisms against microorganisms and foreign agents is based.

White blood cells, in fact, are the main protagonists of our immune system, which every day takes care of defending the body, not only from the aggression of foreign bodies, but also from bacteria, viruses and invaders, which could constitute a risk for the development of even serious diseases. The immune response is the first reaction that the body implements to fight pathogens, which could cause an infection.

The body’s defenses are not only extremely efficient, but also coordinated: white blood cells can communicate through specific proteins, such as cytokines.

In the absence of a healthy and strong immune system, even drug therapies, such as corticosteroids and antibiotics, would not be able to defeat a serious infection. The first weapon of prevention against disorders and diseases, therefore, is to take care of leukocytes and their immune defenses, limiting the risks of infections as much as possible. Starting from the skin, it is always good to disinfect cuts and wounds, which constitute an open door for the entry of dirt and microorganisms.

Leukocytes, as well as other corpuscular elements of the blood, are all generated in the bone marrow from a single type of progenitor stem cell, called hemocytoblast, through a process of differentiation of the different cell lines that is called hematopoiesis.

Unfortunately, the immune system can also experience disorders that undermine its effectiveness and functioning. Among the most well-known pathologies are, for example, leukemias: blood cancers that cause uncontrolled production of leukocytes. In this case, a white blood cell count test can help diagnose this type of disorder in time. If a condition of leukocytosis (increased number of white blood cells) is confirmed, this could be an indication of the presence of a form of leukemia.

Different and specialized

The five types of leukocytes found in the blood are:

• neutrophil granulocytes;
• eosinophilic granulocytes;
• basophilic granulocytes;
• lymphocytes;
• monocytes;

In turn, the subpopulation of lymphocytes can be divided into three distinct groups based on their immune skills: B lymphocytes, T lymphocytes and NK (natural killer) lymphocytes.

Neutrophil granulocytes are the most numerous among circulating leukocytes, of which they constitute a share that is normally equal to 50-70% of the total. They implement the first response against bacterial and fungal infections and are the immune cells most present in inflammatory foci that form in tissues in the presence of foreign agents to the body.

Eosinophilic granulocytes, present in low numbers in circulating blood (<4%), are instead widely distributed at the level of the mucous membranes that can be exposed to germs, allergens and foreign substances, such as digestive, genital, urinary and upper airways. They perform a defense function against parasitic infections and are involved in allergic reactions.

Basophilic granulocytes are the rarest among circulating leukocytes (<2%). They are the main actors of allergic reactions, as they release histamine and heparin, and cooperate in defense against infections by producing chemical mediators that attract other leukocytes.

Lymphocytes are well represented in the blood (20-50%), but even more widely in the lymphatic system. They are responsible for acquired immunitya (or adaptive), that is, the most specialized and specific immune responses, which are defined cell-mediated, in the case of T and NK lymphocytes, or humoral, in the case of B lymphotics, the only ones to produce and put antibodies into circulation.

Monocytes are the most voluminous among leukocytes. Present in the blood in fair quantities (5-8%), they have the ability to migrate, crossing the walls of blood vessels, into the tissues where inflammatory processes are taking place. From monocytes derive macrophages, which have the ability to engulf microorganisms or foreign particles. Phagocytosis helps in the process of recovery from infections, allowing to dispose of the waste of pathogens that died during the immune response.

The wide variety of white blood cells within the body allows it to respond quickly to numerous infections. However, the effectiveness of the immune system can be compromised even without a change in the number of leukocytes. For example, in a patient suffering from diabetes, the immune response may be weaker. In addition, high blood sugar levels create an environment conducive to the reproduction of pathogens and for the onset of a bacterial infection.

In other cases, a syndrome could lead the immune system to attack organs and systems of the body for no reason, causing damage. This is the case of Crohn’s disease: a disease that causes white blood cells to attack the intestinal walls, triggering a strong inflammation.

Values in the blood

For diagnostic purposes, the leukocytes that are usually considered to be those present in the blood, of which the quantity, overall and for the individual subpopulations, and the morphological characteristics of the cellular elements are evaluated.

The laboratory analysis that provides the quantitative data is the blood count accompanied by the leukocyte formula, i.e. the determination of the percentage and number per unit of measurement of blood (liter / microliter / cubic millimeter) of the various types of white blood cells.

Qualitative data, on the other hand, are collected through microscopic observation of the structural characteristics of individual cells.

The reference values may vary depending on the laboratory performing the analysis, which may use different units of measurement.

Below is an example of the values of the leukocyte formula (percentage and number per cubic millimeter) that in adults are considered normal:

As mentioned above, an excessive number of white blood cells could make you suspect the presence of a bone marrow disorder, and therefore a form of leukemia.

At the same time, a situation of leukopenia (lower than normal white blood cell count) could be the clue to other forms of disease. Among these, we always find leukemias, such as myeloid, but also the effect of treatments and cures for cancer, such as chemotherapy.

Inflammation of the apparatus responsible for the production of white blood cells could also lead to a condition of leukopenia. One organ to pay special attention to is the spleen, as well as the lymph nodes, tonsils and thymus.

Obviously, before taking precautions, it is of fundamental importance to seek the advice of your doctor. This will be able to prescribe a sample, to check the levels of leukocytes in the blood and detect the possible presence of immune system disorders. In case of symptoms, the specialist can define the cause, and provide useful advice to start a specific therapy.