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How does HIV damage the immune system over time?

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HIV damages the immune system by specifically targeting and depleting helper T cells (also known as CD4+ T cells). These cells are essential for a healthy immune response because they produce factors that activate other immune cells, including B lymphocytes, which create antibodies, and cytotoxic T lymphocytes, which destroy infected cells.12

The virus functions as a retrovirus, using the host cell's machinery to replicate. It binds to the CD4 protein on the surface of helper T cells to gain entry, where it integrates its genetic material into the host's DNA. As the virus replicates, it destroys the infected helper T cells. Over time, the rate at which these cells are lost exceeds the body's ability to produce new ones, leading to a progressive decline in the CD4 count.123

As the immune system weakens, the body loses its ability to defend against pathogens. When the CD4 count drops below 200 cells per microlitre of blood, the patient is diagnosed with AIDS, leaving them vulnerable to life-threatening opportunistic infections and certain cancers.234