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How does HIV make people with AIDS vulnerable to opportunistic infections?

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Tuberculosis — disease A doctor examining chest X-rays of patients infected with tuberculosis, which remains one of the world's deadliest diseases.

Human immunodeficiency virus (HIV) causes AIDS by systematically attacking and destroying the immune system, specifically targeting helper T cells (also known as CD4+ T cells).123

These cells are critical to the immune response because they produce factors that activate other essential immune cells, including B lymphocytes, which produce antibodies, and cytotoxic T lymphocytes, which destroy infected cells. As HIV replicates, it depletes the number of helper T cells.2

AIDS is diagnosed when this count drops below 200 cells per microlitre of blood. At this stage, the immune system is so severely compromised that it can no longer defend the body against pathogens that a healthy immune system would typically suppress. This vulnerability allows opportunistic infections—such as tuberculosis, toxoplasmosis, and cytomegalovirus—to arise and devastate the body. Ultimately, individuals with AIDS often succumb to these infections or to malignancies like Kaposi sarcoma that the body can no longer fight.435