Pathology
Pathology/A/42
AIDS
後天性免疫不全症候群（AIDS）
- タグ
- High-yield / ポイント
1. Definition
AIDS is a retroviral disease caused by HIV. Infection and progressive depletion of CD4⁺ T cells → severe immunosuppression → opportunistic infections, neoplasms, and neurological disease.
Transmission: sexual; parenteral (IV drug use, transfusion, needlestick); transplacental/perinatal (in utero, delivery, breast milk).
2. Virus structure & entry
- Cone-shaped core: capsid protein p24 (diagnostic antigen), nucleocapsid p7/p9, 2 RNA copies (genes gag, pol, env), enzymes reverse transcriptase, integrase, protease.
- Envelope glycoproteins gp120 and gp41.
- Entry: gp120 binds CD4 (high-affinity receptor) + a co-receptor (CCR5 early/macrophage-tropic; CXCR4 late/T-tropic) → conformational change → gp41 mediates membrane fusion.
- Life cycle: reverse transcription → cDNA → integration as provirus → latency or transcription → new virions bud.
3. Clinical course
| Phase | Features |
|---|---|
| Primary / prodrome (2–4 wk) | Infects macrophages + CD4 T cells (CCR5); flu-like illness, lymphadenopathy, fever |
| Latent (up to ~10 yr) | Ongoing replication in lymph nodes; asymptomatic |
| AIDS | Steep CD4 decline; diagnosed when CD4 <200; CXCR4 switch; opportunistic infections + cancers |
Monitoring: HIV Ag/Ab test → confirmation; CD4 count predicts OI risk; viral load tracks treatment response.
4. Opportunistic infections (by CD4 count)
| CD4 | Infection |
|---|---|
| <200 | Pneumocystis jirovecii pneumonia; oral/esophageal candidiasis |
| <100 | Toxoplasma encephalitis; Cryptococcus meningitis |
| <50 | MAC (atypical mycobacteria); CMV retinitis |
Also TB, HSV, disseminated CMV.
5. AIDS-defining malignancies & CNS
- Kaposi sarcoma (HHV-8), non-Hodgkin lymphoma (EBV — Burkitt, DLBCL), invasive cervical/anal cancer (HPV).
- CNS: aseptic meningitis, viral meningoencephalitis, AIDS dementia complex.
- Treatment: antiretroviral therapy (ART) + OI prophylaxis.
💡 High-yield: HIV uses gp120–CD4 + CCR5 (early) / CXCR4 (late); gp41 fusion; p24 antigen. AIDS = CD4 <200. OIs by count: PCP <200, Toxo <100, MAC/CMV <50. Cancers: Kaposi (HHV-8), NHL (EBV), cervical (HPV). Treat with ART.