What is CD4 lymphocytes and why is their number so important, every HIV-positive patient knows. For most of us, this concept is unknown. In the article we will talk about white blood cells, CD4 and CD8 lymphocytes, their value and normal values.
Our main defenders
Lymphocytes are one of the varieties of white blood cells and our most important immune cells, which protect the body from viral, bacterial, fungal infections, produce antibodies, fight cancer cells and coordinate the work of other immune response agents.
Lymphocytes come in 3 types:
- B-lymphocytes are “spies” of the immune system. Once they met with the pathogen, they remember it. It is thanks to them that we develop immunity to the diseases that we have been ill with. They are about 10-15%.
- NK-lymphocytes - "KGB" of our body. They track "traitors" - infected body cells or cancer cells. They are about 5-10%.
- T-lymphocytes are the “soldiers” of our immunity. There are many of them - about 80%, they detect and destroy pathogens that enter our body.
general characteristics
All lymphocytes have sizes from 15 to 20 microns in diameter. The volume of the cytoplasm is large, and the nucleus is irregular in shape with light chromatin. T-lymphocytes and B-lymphocytes can be distinguished only when using immunomorphological methods.
All of them are capable of phagocytosis and can penetrate through blood vessels into the intercellular and interstitial fluids.
On the surface of the membranes of T-lymphocytes are protein receptors that are associated with the molecules of the main histocompatibility complex of a person. It is these coreceptors that determine the functions and tasks that solve various types of white blood cells.
The average life expectancy of 3-5 days, they die either at the site of the inflammatory process, or in the liver and spleen. And everything is formed in the bone marrow from hematopoietic precursors.
T-lymphocytes: directions of protection
This large army works for the benefit of us in several directions:
- T-killers directly destroy viruses, bacteria, fungi that enter the body. On their membrane are special CD8 coreceptor proteins.
- T-helpers enhance the body's defensive response and transmit information about a foreign agent to B-lymphocytes so that they produce the necessary antibodies. On the surface of their membranes is CD4 glycoprotein.
- T-suppressors regulate the strength of the body's immune response.
We are interested in the work and significance of CD4 helper T cells. It is about the specifics of these assistants that we will talk in detail.
A little more about lymphocytes
All lymphocytes are formed in the bone marrow from specific hematopoietic stem cells (hematopoietic stem cell, from the Greek words haima - blood, poiesis - creation). B-lymphocytes undergo maturation in the bone marrow, but T-lymphocytes in the thymus or thymus, which is why they got their name.
The abbreviation CD stands for cluster of differentiation - clusters of differentiation. These are specific proteins on the surface of cell membranes, of which there are several dozen species. But CD4 and CD8 are most often investigated, as they are of significant diagnostic value.
HIV and CD4 lymphocytes
It is the T-helpers that are the target for the attack of the human immunodeficiency virus. In these cells of the immune system, the virus invades and embeds its DNA into the lymphocyte DNA. Lymphocyte cd4 dies and gives a signal to increase the production of new T-helpers. This is exactly what the virus needs - it immediately penetrates into young lymphocytes. As a result, we have a vicious circle with which our immunity cannot cope, like all modern medicine.
Norm and tasks
Having data on the number of CD4 T-lymphocytes in the patient’s blood, it can be concluded that the immune system is healthy. If there are few of them, the immune system is not in order.
The normal number of CD4 lymphocytes in a cubic millimeter of blood is from 500 to 1500 units. Counting them is especially important for HIV-positive people. It is precisely by the number of CD4 lymphocytes in the patient’s blood that the doctor decides to start antiretroviral therapy.
In patients with HIV, if untreated, the number of helpers in the blood decreases by 50-100 cells per year. When the number of CD4 lymphocytes in the blood is less than 200 units, patients begin to develop AIDS-associated diseases (for example, pneumocystis pneumonia).
Helper share in blood test
For an ordinary person, it is not the number of these cells that matters, but their proportion in the blood, and it is precisely such a graph that is more common in the results of a blood test. In a healthy person, the proportion of CD4 lymphocytes in the blood is 32-68% of the total number of all white blood cells.
It is the indicator of the share of T-helpers that is often more accurate than their direct calculation. For example, the number of helpers in the blood can vary over the course of several months from 200 to 400, but their proportion is 21%. And while this indicator does not change, we can assume that the immune system is normal.
If the proportion of CD4 T-lymphocytes decreases to 13%, regardless of their number, this means that significant damage has appeared in the functioning of the human immune system.
Immune status
The results of the analysis can also indicate the ratio of T-helpers to T-killers - CD4 + / CD8 + (the number of CD4 lymphocytes divided by the number of cd8 lymphocytes). HIV-positive people are characterized by low CD4 counts and high CD8 counts, and, accordingly, their ratio will be low. Moreover, if in the process of treatment this indicator increases, then this indicates that drug therapy is working.
The normal ratio of CD4 to CD8 lymphocytes is from 0.9 to 1.9 in the general analysis of human blood.
Clinical diagnostic value
Determination of the number and content of the main groups and subpopulations of lymphocytes in the patient’s blood is important for immunodeficiency conditions, lymphoproliferative pathologies, and HIV infection.
CD4 lymphocyte counts may increase with other immune activations, such as infections or transplant rejection.
Data on the number and ratios of these subpopulations of lymphocytes are used to confirm or refute the diagnosis, to monitor the functioning of the immune system, to predict the severity and duration of the disease and evaluate the effectiveness of therapy.
When is analysis necessary?
The main indications for a blood test for the number of CD4 lymphocytes are as follows:
- Infectious diseases with a chronic and protracted course, frequent relapses.
- Suspicion of congenital or acquired immunodeficiency.
- Autoimmune diseases.
- Oncological pathologies.
- Allergic diseases.
- Examination before and after transplantation.
- Examination of patients before major abdominal surgery.
- Complications in the postoperative period.
- Monitoring of antiretroviral therapy, the effectiveness of cytostatics, immunosuppressants and immunomodulators.
Preparation and analysis
The biomaterial for clinical diagnostic analysis is the venous blood of the patient. Before donating blood for the determination of CD4 + / CD8 +, smoking and exercise must be excluded. Blood is taken on an empty stomach, the last meal - at least 8 hours before analysis.
Children under five years of age and patients who are contraindicated in fasting are allowed to eat light food two hours before the analysis.
Interpretation of the result
The CD4 + / CD8 + ratio is higher than normal in diseases such as lymphocytic leukemia, thymoma, Wegener's disease, and Cesari's syndrome. An increase in the number of cells may indicate a significant viral load and autoimmune reactions.
This indicator increases with mononucleosis, which is caused by the Epstein-Barr virus, chronic lymphocytic leukemia, myasthenia gravis, multiple sclerosis, and HIV infection.
Ratios in the region of three are often observed during the acute phase of various infectious diseases. In the middle of the inflammatory process, a decrease in the number of T-helpers and an increase in the number of T-suppressors are more often observed.
A decrease in this indicator due to an increase in the number of suppressors is characteristic of some tumors (Kaposi's sarcoma) and systemic lupus erythematosus (a congenital defect in the immune system).