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

The immune system, made up 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 body's primary biological barriers, the immune system encompasses secondary and tertiary defense.

Our body is not a watertight compartment, since the airways and the mouth, for example, are ideal conduits for the entry of pathogens into 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 data underlines that, of course, our immune system fights against pathogens in practically every moment of our life. Lymphoblasts are the precursors of lymphocytes, the immune cells par excellence. If you want to know everything about them, keep reading.

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

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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.

Anyway, as soon as we start we find a clear terminological conflict, since a lymphoblast it also refers to a lymphocyte that has become enlarged after being stimulated by an antigen. Both events are completely different, but the same word is used to designate them. We detail each one of them in the following lines.

1. The lymphoblast as a precursor

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

In general terms, we can describe the transformation from lymphoblast to functional lymphocyte in the following steps:

The maturation of lymphoblasts or common lymphocytic progenitors in the bone marrow leads to compromise in the B or T lymphocyte lineages.
Immature lymphocytes proliferate in various stages during their maturation. For example, proliferation of prolymphocytes occurs to ensure the provision of an adequate number of cells to later mature.
Lymphocytes are selected through multiple steps during their maturation in order to preserve useful specificities 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 all this process, lymphocytes present receptors for specific antigens, which enables them to produce antibodies. and therefore 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 we have said, they 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 the same. 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 what is described here, but it is enough for us to show a general image of it.

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2. The lymphoblast as a lymphocyte with altered morphology

On the other side of the coin, and confusing as it sounds, a lymphocyte that has become enlarged after being stimulated by an antigen is also called a lymphoblast. In this case, when recognizing the antigen, this type of white blood cell is activated, which causes growth at the cytoplasmic and nuclear levels 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 first activated it instance. Finally, the cells obtained can be differentiated into specific cell types that will fight the pathogen in one way or another.

You may be interested in: "Major Cell Types of the Human Body"

Characteristics of a lymphoblast

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

The lymphoblast is between 10 and 18 microns in size.
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 between 1 and 2 nucleoli, regions of the cell nucleus that are responsible for the production and assembly of ribosomes in cells.

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 an uncontrolled proliferation of lymphoblasts occurs (again, if we conceive lymphoblast as a precursor of a lymphocyte), these invade the bone marrow preventing the manufacture of other cells, such as red blood cells and platelets. This pathology is known as acute lymphoblastic leukemia (ALL) and it is very dangerous to health.

This pathology does not know gender, ethnicity or age, although it is very rare to present it, since foundations calculate that its prevalence is 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 It is caused by the mutation of a single lymphoblast in the bone marrow that triggers the reaction described aboveBut researchers around the world have yet to discover what is really driving 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 promote ALL symptoms:

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

Not everything is bad news at first glance, well survival rates for patients with acute lymphoblastic leukemia 5 years after diagnosis less than 20 years of age is 90%. Unfortunately, if we analyze data from patients over 20 years of age, the 5-year survival rate after diagnosis is less than 40%. All these data are only estimates, since each case depends on the physiological characteristics of the individual and their development of the disease.

A terminological confusion

As indicated by the Chronic Lymphoblastic Leukemia Research Consortium, a lymphoblast is defined as “a lymphocyte that has grown 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 bibliographic sources use the term lymphoblast as a precursor, which is transforms into a prolymphocyte and this will give rise to the well-known B and T lymphocytes responsible for the immune response.

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

Bibliographic references:

What is acute lymphoblastic leukemia?, Spanish Association of People Affected by Lymphoma, Myeloma and Leukemia. Picked up on December 13 in http://www.aeal.es/leucemia-linfoblastica-aguda-espana/2-que-es-la-leucemia-linfoblastica-aguda/
ATLAS OF HEMATOLOGY, collected on December 13 in http://www.qualitat.cc/sitebuildercontent/sitebuilderfiles/atlas.hematologia.pdf
Definition of lymphoblast, National Cancer Institute (NIH). Picked up on December 13 in https://www.cancer.gov/espanol/publicaciones/diccionario/def/linfoblasto
Lymphoblast, the free dictionary. Picked up on December 13 in https://es.thefreedictionary.com/linfoblastos
Immune System, Radyschildren.org. Picked up on December 13 in https://www.rchsd.org/health-articles/sistema-inmunolgico-3/#:~:text=El%20sistema%20inmunol%C3%B3gico%20es%20la, % 20body% 20 and% 20 cause% 20 disease.
Vásquez Palacio, G., Ramírez Castro, J. L., Posada Díaz, A., Sierra, M., Botero, O. L., Durango, N. AND.,... & Tabares, J. G. (2002). Acute lymphoid leukemia: cytogenetic study in children treated at the San Vicente de Paúl University Hospital in Medellín in the period 1998-2001. Iatreia, 15 (4), 217-225.