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How does HIV cause acquired immune deficiency syndrome?

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immune system disorder False-color scanning electron micrograph of a T cell infected with HIV (human immunodeficiency virus), the agent that causes AIDS (acquired immunodeficiency syndrome).

HIV causes acquired immunodeficiency syndrome (AIDS) by systematically destroying the body's immune system, specifically targeting helper T cells (also known as CD4+ T cells).12

These cells are critical for coordinating immune responses, including the activation of B lymphocytes and other effector cells. HIV infects these cells by binding its gp120 protein to the CD4 receptor on the T cell surface, often utilizing coreceptors like CCR5 or CXCR4 to enter the cell. Once inside, the virus integrates its genetic material into the host cell's DNA, hijacking the cell to produce new viral particles.2

As the virus replicates, it kills the infected helper T cells. When the number of these cells drops below 200 cells per microlitre of blood, the immune system is considered severely compromised. This depletion leaves the body unable to defend itself against opportunistic infections—microbes that a healthy immune system would typically eliminate—which characterizes the onset of AIDS. While there is no cure, antiretroviral therapy can suppress viral replication and prevent this progression.2341