Linfócites: what they are and why they may be altered

Lymphocytes are a type of defense cell in the body, also known as white blood cells, which are produced in greater quantity when there is an infection, being therefore a good indicator of the patient's he alth status. There are two types of lymphocytes, B cells and T cells, which play different roles in the immune system.

The number of lymphocytes can be evaluated by means of a blood test, so that when they are increased it is usually indicative of infection, while the decrease in the number of lymphocytes may be related to some alteration in the bone marrow.

Thus, it is important that the blood test be evaluated by the doctor so that it is possible to assess the general state of he alth of the person and relate the results obtained with the clinical history, so that it is possible to make the diagnosis and start the most appropriate treatment, if necessary.

Altered lymphocytes

The normal reference values for lymphocytes are between 1000 to 3900 lymphocytes per mm³ of blood, which represents 20 to 50% in the relative count, and may vary according to the laboratory where the test is performed. When the values are above or below the reference value, a picture of lymphocytosis or lymphopenia, respectively, is characterized.

1. High lymphocytes

The amount of lymphocytes above the reference values is called lymphocytosis and is usually related to infectious processes. Thus, the main causes of high lymphocytes are:

Acute infections such as mononucleosis, polio, measles, rubella, dengue or whooping cough, for example;
Chronic infections such as tuberculosis, malaria;
Viral hepatitis;
Hyperthyroidism;
Pernicious anemia, which is characterized by deficiency of folic acid and vitamin B12;
Benzene and heavy metal poisoning;
Diabetes;
Obesity;
Allergy.

In addition, the increase in the number of lymphocytes can also happen due to physiological situations, such as pregnant women and infants, in addition to nutritional deficiencies, such as vitamin C, D or calcium deficiency.

2. Low lymphocytes

The amount of lymphocytes below the reference values is called lymphopenia and is usually related to situations involving the bone marrow, such as aplastic anemia or leukemia, for example. In addition, lymphopenia can also be a sign of autoimmune diseases, in which the body itself acts against the immune defense system, such as systemic lupus erythematosus, for example (SLE).

Lymphopenia can still happen due to AIDS, immunosuppressive drug therapy or chemotherapy or radiotherapy treatment, rare genetic diseases, or as a consequence of stressful situations, such as postoperative and body overload, for example.

The decrease in lymphocyte values can also be a consequence of COVID-19, in which the presence of the virus in the body can lead to the destruction of lymphocytes. However, for confirmation of COVID-19, other blood tests are necessary, in addition to a positive result in the molecular test. Understand how the diagnosis of COVID-19 is made.

Types of lymphocytes

There are 2 main types of lymphocytes in the body, B lymphocytes, which are immature cells produced in the bone marrow and released into the bloodstream to produce antibodies against bacteria, viruses and fungi, and T lymphocytes, which are produced in the bone marrow but then develop in the thymus until they are divided into 3 groups:

CD4 T lymphocytes: help B lymphocytes to eliminate infections, being the first alert of the immune system. Usually these are the first cells to be affected by the HIV virus, and in infected patients the blood test indicates a value lower than 100/mm³.
CD8 T lymphocytes: decrease the activity of other types of lymphocytes and, therefore, are increased in cases of HIV;
Cytotoxic T lymphocytes: destroy abnormal cells and cells infected by viruses or bacteria.

However, lymphocyte type tests, especially the CD4 or CD8 type, should always be interpreted by a doctor to assess whether there is a risk of having HIV, for example, since other diseases can also cause the same type of changes.

So, if there is any doubt about being infected with HIV, it is advisable to do a laboratory test that looks for the virus inside the body's cells. Learn more about HIV testing.

What are atypical lymphocytes?

Atypical lymphocytes are lymphocytes that have a varied shape and that normally arise when there are infections, especially viral infections, such as mononucleosis, herpes, AIDS, rubella and chickenpox. In addition to the appearance in viral infections, atypical lymphocytes can be identified in the blood count when there is a bacterial infection, such as tuberculosis and syphilis, infection by protozoa, such as toxoplasmosis, when there is hypersensitivity to drugs or in autoimmune diseases, as in lupus.

Usually the number of these lymphocytes returns to normal (reference value of atypical lymphocytes is 0%) when the agent causing the infection is eliminated.

These lymphocytes are considered activated T lymphocytes that are produced in response to infected type B lymphocytes and perform the same functions as typical lymphocytes in the immune response. Atypical lymphocytes are generally larger than normal lymphocytes and vary in shape.