CD4 and T cells are a subset of white blood cells. Known like this thanks to a protein on their surfaces, they play an important role in the immune system.
CD4 T cells and why they are important
CD4 is, in contrast, a type of protein found in certain cells of the immune system. Among them are T cells, macrophages and monocytes.
CD4 T cells are considered “helper” cells because they do not neutralize infections. however, they trigger the immune response to infections. And CD8 T cells - classified as such due to the type of protein on its surface they kill the aggressors, producing antibodies that help to fight invaders.
Role of CD4 T cells in HIV infection
Therefore, one of the puzzles of HIV infection is that the cells destined to initiate an immune defense are the same cells destined for HIV infection. HIV.
Like a retrovirus, HIV needs to infect certain "host" cells to make copies of itself. Thus, CD4 cells are the main targets for this during an infection.
During infection, HIV binds to these helper cells, emptying their genetic material so that the host's genetic code can be changed to produce other HIV virions.
Therefore, in doing so, the host CD4 cell ends up being killed. And the infected person's ability to trigger an immune defense is gradually reduced to the point of leaving his body vulnerable to opportunistic infections.
The dynamics of HIV is such that the “killer” CD8 T cells are increasingly blinded by the spread of infection and eventually become unable to cope with the growing HIV population, measured by viral load.
If an HIV infection is left untreated, the immune system, in all but rare cases, will completely collapse (or be compromised).
Types of CD4 T cells
Most of the time, we tend to think of CD4 T cells as a type of cell. In fact, it was only in the mid-1980s that scientists began to identify several subsets with different functions. Some are important in activating macrophages and dendritic cells during initial infection, while others direct immune defenses when confronted, individually, with parasitic organisms, bacteria or viruses.
These include subtypes called
- T-helper 1,
- T-helper 2,
- T-helper 9,
- T-helper 17,
- regulatory T cell and
The auxiliary follicular T cell has many variables, and each of which secretes different types of substances to help neutralize offending agents.
Diagnostic value of CD4 T cells
By determining how many functioning CD4 cells are circulating in the blood, the doctor can determine the state of a person's immune system. A simple blood test called a CD4 count estimates the number of CD4 cells functioning in one cubic millimeter of blood. The higher the CD4 count, the stronger the immune function.2
In a healthy adult, a normal CD4 count can vary enormously (by population, age group, etc.), but it is typically about 500 to 1500 cells per cubic millimeter of blood (ml).
When it is below 200, however, the disease is technically classified as AIDS (acquired immunodeficiency syndrome).3It is during this period that the most serious opportunistic infections occur, since the immune system is effectively compromised by the infection.
CD4 and CD4 T cells in ART monitoring
Before 2016, CD4 counts were used as a means of determining when to start ART. But in recent years, that role has changed, as global authorities now endorse the immediate start given HIV therapy in diagnosis (instead of waiting until the CD4 count drops below 500 cells / mL, as was the previous guideline).4
The CD4 count is also used to monitor an individual's response to therapy, with early initiation of antiretroviral therapy, in general, capable of restoring a person's immune function.
On the other hand, people who start therapy with very low CD4 counts, below 100, tend to have a harder time restoring their CD4 counts to normal levels, especially after a severe episode of illness.5
It is therefore important to get tested and seek immediate care in the event of an HIV-positive diagnosis. If treatment is started immediately, people living with HIV now have a much better chance of living a normal, healthy life.
Reading suggested by the system
- Luckheeram R. Zhou R, Verma A, et al. CD4 + T cells: differentiation and functions. Clinical and Developmental Immunology. 2012: 2012: 925135. doi: 10.1155 / 2012/925135
- Institute of Medicine (US) Committee on Social Security HIV Disability Criteria. 3, low CD4 count as an indicator of deficiency. HIV and disability: updating social security lists. Washington (DC): National Academies Press (USA); 2010.
- US Department of Veterans Affairs. CD4 count (or T cell count).
- National Institutes of Health (NIH). Early initiation of antiretroviral therapy improves outcomes for HIV-infected individuals. Bethesda, Maryland; issued on May 27, 2015.
- Seng R, Goujard C, Krastinova E.; et al. Lifetime cumulative HIV viremia influence on long-term recovery of CD4 + count and CD4 + / CD8 + ratio among patients on combination antiretroviral therapy. AIDS. 2015; 29(5): 595-607. DOI: 10.1097 / QAD.0000000000000571.