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How does HIV invade the human body? The secrets of CD4 and virus attack revealed!
In our immune system, the term CD4 is no stranger. This is a glycoprotein expressed on the surface of T lymphocytes and is essential for our body's immune defense function. In this article, we will explore the structure and function of CD4, and how HIV uses this protein to invade the human body.
Structure and function of CD4
CD4 is a member of the immunoglobulin superfamily and has four immunoglobulin domains, namely D1 to D4. These structures on the outside of the cell are open to the external environment and help CD4 interact with the MHC II molecules of the antigen-presenting cell.
The D1 domain of CD4 binds to the β2 region of MHC II. This tight binding promotes signaling between the T cell receptor (TCR) and antigen-presenting cells.
Through this process, CD4 can not only increase the affinity of TCR, but also help recruit and activate other signal transduction proteins, such as ZAP70, ultimately promoting T cell activation.
HIV Invasion Strategy
When it comes to the HIV virus, CD4's role is even more obvious. HIV-1 initiates the invasion process through the binding of its envelope protein gp120 to CD4. This binding triggers a conformational change in gp120, allowing it to bind to a co-receptor on the surface of the host cell, usually CCR5 or CXCR4.
Once gp41 undergoes structural changes, HIV can insert the fusion peptide into the host cell and fuse with its cell membrane to complete invasion.
After this series of reactions, HIV begins to replicate itself in the host cells, causing the number of CD4+ T cells to gradually decrease, ultimately damaging the host's immune system.
The pathology of HIV and its effects
The process of HIV infection will gradually reduce the number of CD4+ T cells. Medical professionals often use CD4 counts to decide when to start treatment. According to the latest medical guidelines, treatment needs to be initiated as soon as HIV infection is diagnosed, regardless of CD4 count.
The normal CD4 cell count range is about 500 to 1200 cells per microliter (cells/mm3). When this value is lower than 200, the patient is at high risk and susceptible to the disease defined by AIDS.
The CD4 count not only reflects the health of the immune system, but can also be used to evaluate the effectiveness of treatment. Generally speaking, during the first two years of receiving anti-HIV treatment, doctors will regularly check the CD4 count to observe changes in the condition.
Other potential diseases and effects
In addition to HIV, CD4 also plays an important role in some other autoimmune diseases, such as type 1 diabetes and vitiligo. In addition, CD4 is also expressed in many tumors derived from T helper cells and can therefore be used for tumor diagnosis.
When testing the efficacy of drugs or studying disease, quantifying T cells and using CD4+, CD8+, CD3+ T cell markers can help medical professionals understand disease progression.
Conclusion
The function of CD4 is not only crucial to understanding the immune system, but also the key to revealing the HIV invasion mechanism. As we gain a better understanding of these mechanisms, we may be able to develop more effective treatment strategies. However, faced with such a complex virus, can we find a way to completely eradicate HIV?
