Lymphoblasts: what are they, characteristics and functions in the human body?

What type of cells are lymphoblasts? What role do they play in the lymphatic system? Let's take a look.

The immune system, composed of cells, proteins, tissues and organs, defends the human species and other complex living beings against germs and microorganisms on a daily basis. If the skin, saliva and mucous membranes are the primary biological barriers of the organism, the immune system encompasses secondary and tertiary defense.

Our body is not a watertight compartment, as the airways and the mouth, for example, are ideal conduits for pathogens to enter our body. Beyond the skin and mucous membranes, therefore, there must be an intricate defense system that protects us once the germ is already inside us.

To give you an idea, approximately 20% of the world's population has the flu at the time you are reading these lines. This fact underscores the fact that our immune system fights pathogens at virtually every moment of our lives. Lymphoblasts are the precursors of lymphocytes, the immune cells par excellence.. If you want to know all about them, read on.

What is a lymphoblast?

According to the National Cancer Institute (NIH), a lymphoblast is defined as an immature cell that serves as a precursor to lymphocytes, the cell bodies responsible for tertiary immune barriers..

However, right from the start we encounter a clear terminological conflict, because a lymphoblast also refers to a lymphocyte that has enlarged after having been stimulated by an antigen. Both events are completely different, but the same word is used to designate them. We will describe each of them in detail in the following lines.

1. The lymphoblast as a precursor

Under normal circumstances, the lymphoblasts (assumed to be the cells that give rise to lymphocytes) are found in the bone marrow of the long bones of healthy people.. If we take the meaning of the term "lymphoblast" as a progenitor, this could be interchangeable with that of "common lymphocytic progenitor", since both give rise to the prolymphocyte, the intermediate form that finally leads to the cell type sought.

Broadly speaking, we can describe the transformation from lymphoblast to functional lymphocyte in the following steps:

• Maturation of lymphoblasts or common lymphocytic progenitors in the bone marrow results in commitment to B or T lymphocyte lineages.
• Immature lymphocytes proliferate at various stages during maturation. For example, proliferation of prolymphocytes occurs to ensure the availability of an adequate number of cells to mature later.
• Lymphocytes are selected through multiple steps during their maturation in order to retain the specificities useful for each occasion.

Without going into overly complex terminology, we will say that this last step refers to the fact that the selection of one lymphocyte or another is based on the expression of intact components of the receptor for the antigen and what they recognize.

At the end of this whole process, the lymphocytes present receptors for specific antigens, which enables them to produce antibodies and thus to destroy abnormal cells (ideally germs and other pathogens). and thus for the destruction of abnormal cells (ideally germs and other pathogens). These cell bodies represent 30% of the total leukocytes in the peripheral Blood and, as mentioned above, represent the tertiary immune barriers.

T lymphocytes act directly on the pathogen and destroy it, while B lymphocytes detect the antigen (a foreign substance, presumably produced by a pathogen) and generate specific antibodies to it. When an antibody binds with its antigen, the invading microorganism loses its pathogenicity. As you can imagine, this whole process is much more complex than described here, but it suffices to show a general picture of it.

2. The lymphoblast as a lymphocyte with altered morphology.

On the other side of the coin, and as confusing as it may sound, a lymphoblast is also called a lymphocyte, a lymphocyte that has enlarged after being stimulated by an antigen is also called a lymphoblast.. In this case, upon recognition of the antigen, this type of white blood cell is activated, causing growth at the cytoplasmic and nuclear level and in the production of messenger RNA and certain proteins.

Thus, the large lymphoblast begins to divide 2-4 times every 24 hours for 3-4 days, giving rise to 1000 clones of the original lymphocyte, with each of the clones presenting specificity for the same antigen that activated it in the first instance. Finally, the cells obtained can be differentiated into specific cell types that will fight the pathogen in one way or another.

Characteristics of a lymphoblast

We have already shown you what a lymphoblast is, but in order to get a general idea of this peculiar cell body, we still need to to describe it at the morphological level. These are some of the most relevant facts about its physiology:

• The lymphoblast ranges in size from 10 to 18 micrometers.
• Its shape is rounded and oval.
• It has a single cell nucleus and a bluish cytoplasm with granulations.
• The nucleus-cytoplasm ratio is between 5:1 and 7:1.
• It also usually has 1 to 2 nucleoli, regions of the cell nucleus that are involved in the production and assembly of the cell's ribosomes.

Acute lymphoblastic leukemia

Leukemias are cancers that occur in cells that would normally differentiate into different types of blood cells, in this case B and T lymphocytes.. When there is an uncontrolled proliferation of lymphoblasts (again, if we think of lymphoblast as a precursor of a lymphocyte), they invade the bone marrow, preventing the production of other cells, such as red blood cells and platelets. This pathology is known as acute lymphoblastic leukemia (ALL) and is very dangerous to health.

This pathology knows no gender, ethnicity or age, although it is very uncommon, as foundations estimate its prevalence to be 1.29 patients per 100,000 inhabitants. Despite being a very rare disease, ALL is the most common type of cancer in children under 20 years of age (almost 60% of leukemias occur in this age group).

Acute lymphoblastic leukemia is caused by the mutation of a single lymphoblast in the bone marrow that triggers the reaction described above.However, researchers around the world have not yet been able to discover what really causes this event. According to the Spanish Association of People Affected by Lymphoma, Myeloma and Leukemia (AEAL), these are some of the risk factors that can favor a case of ALL:

• Genetic factors, i.e., individual chromosomal alterations determined from the time of the patient's birth.
• Being exposed to X-rays or ionizing radiation before or after birth.
• Having had a treatment based on chemotherapy.
• Infections by some types of viruses (specifically some types of retroviruses).
• Being in contact with certain chemicals, such as benzene and certain alkylating compounds.

It is not all bad news at first glance. survival rates for patients with acute lymphoblastic leukemia under 20 years of age 5 years after diagnosis is 90%.. Unfortunately, if we analyze the data of patients older than 20 years, the survival rate 5 years after diagnosis is less than 40%. All these data are only estimates, as each case depends on the physiological characteristics of the individual and the development of the disease.

Terminological confusion

As indicated by the Chronic Lymphoblastic Leukemia Research Consortium, a lymphoblast is defined as "a lymphocyte that has become larger after being stimulated by an antigen. Lymphoblasts look like immature lymphocytes, and were once thought to be precursor cells." So what are we left with? Multiple literature sources use the term lymphoblast as a precursor, which transforms into a prolymphocyte and this will give rise to the well-known B and T lymphocytes in charge of the immune response.

On the other hand, for other sources such as the one just cited, a lymphoblast is a stimulated lymphocyte, not a precursor. Of course, spaces like this make it clear that, in some specific cases, the medical terminology of a particular event does not necessarily have to be the same in all the sources consulted.

Bibliographic references:

• What is acute lymphoblastic leukemia, Asociación Española de Afectados por Linfoma, Mieloma y Leucemia. Retrieved on December 13 from http://www.aeal.es/leucemia-linfoblastica-aguda-espana/2-que-es-la-leucemia-linfoblastica-aguda/
• ATLAS DE HEMATOLOGÍA, retrieved on December 13 from http://www.qualitat.cc/sitebuildercontent/sitebuilderfiles/atlas.hematologia.pdf
• Definition of lymphoblast, National Cancer Institute (NIH). Retrieved December 13 from https://www.cancer.gov/espanol/publicaciones/diccionario/def/linfoblasto
• Lymphoblast, the free dictionary. Retrieved Dec. 13 from https://es.thefreedictionary.com/linfoblastos.
• Immune system, Radyschildren.org. Retrieved 13 December from https://www.rchsd.org/health-articles/sistema-inmunolgico-3/#:~:text=The%20immune%20system%20immune%20C3%B3gic%20is%20it%20the%20body%20and%20causes%20diseases.
• Vásquez Palacio, G., Ramírez Castro, J. L., Posada Díaz, A., Sierra, M., Botero, O. L., Durango, N. E., ... & Tabares, J. G. (2002). Acute lymphoid leukemia: cytogenetic study in children attended at the Hospital Universitario San Vicente de Paúl de Medellín in the period 1998-2001. Iatreia, 15(4), 217-225.