Why People with AIDS Develop Opportunistic Infections

HIV selectively infects and destroys CD4⁺ T-helper lymphocytes, the orchestrators of adaptive immunity. As CD4 count falls (<200 cells/µL = AIDS), cell-mediated immunity collapses, permitting opportunistic pathogens—normally controlled by intact immunity—to cause disease.

Major Opportunistic Infections (OIs) by CD4 Threshold

CD4 Count	Typical OIs
<200	Pneumocystis jirovecii pneumonia (PCP), Kaposi sarcoma, esophageal candidiasis
<100	Toxoplasma encephalitis, cryptococcal meningitis, CMV retinitis, disseminated MAC
<50	Disseminated CMV, MAC, progressive multifocal leukoencephalopathy (JCV)

Other Complications

• Malignancies: Kaposi sarcoma (HHV-8), non-Hodgkin lymphoma (EBV), cervical/anal cancer (HPV).
• Wasting syndrome, HIV-associated nephropathy, neurocognitive disorder.

Impact of Antiretroviral Therapy (ART)

• Suppresses HIV replication → CD4 recovery → immune reconstitution.
• OI incidence dropped >90% since combination ART (1996).
• Prophylaxis guidelines (e.g., TMP-SMX for PCP if CD4<200) can be discontinued after sustained CD4>200 on ART.

Key Message

Early HIV diagnosis, prompt ART initiation, and adherence transform AIDS from a fatal immunodeficiency to a manageable chronic condition.