Acquired Immune Deficiency Syndrome (AIDS) | 获得性免疫缺陷综合征（艾滋病）

📚 Acquired Immune Deficiency Syndrome (AIDS) | 获得性免疫缺陷综合征（艾滋病）

Acquired immune deficiency syndrome (AIDS) is the most serious clinical consequence of infection by the human immunodeficiency virus (HIV). In Cambridge International A Level Biology, HIV is studied as an example of a retrovirus that attacks the immune system, especially CD4⁺ T helper lymphocytes. Understanding its structure, replication cycle and diagnosis illustrates key principles of virology, immunology and public health.

获得性免疫缺陷综合征（AIDS，艾滋病）是人类免疫缺陷病毒（HIV）感染后最严重的临床结局。在剑桥国际 A Level 生物课程中，HIV 被作为一种攻击免疫系统（尤其是 CD4⁺ 辅助性 T 淋巴细胞）的逆转录病毒实例来学习。理解其结构、复制周期和诊断方法有助于说明病毒学、免疫学和公共卫生的核心原理。

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1. HIV and AIDS: Definitions and Relationship | HIV 与 AIDS 的定义及关系

HIV is a retrovirus whose genetic material is RNA. Once inside a host cell, it converts its RNA into DNA using the enzyme reverse transcriptase. AIDS is the late stage of untreated HIV infection, defined by a very low CD4⁺ T cell count and/or the appearance of opportunistic infections or certain cancers.

HIV 是一种遗传物质为 RNA 的逆转录病毒。进入宿主细胞后，它利用逆转录酶将 RNA 转化为 DNA。AIDS 是未经治疗的 HIV 感染的晚期阶段，定义为 CD4⁺ T 细胞计数极低和/或出现机会性感染或某些肿瘤。

Being HIV-positive means the person carries the virus; it does not automatically mean the person has AIDS. With modern treatment, an HIV-positive individual may never develop AIDS.

HIV 阳性意味着携带病毒，但并不意味着已患艾滋病。通过现代治疗，HIV 阳性者可能终身不会发展为艾滋病。

Feature 特征	HIV infection HIV 感染	AIDS 艾滋病
Nature 性质	Viral infection by HIV 由 HIV 引起的病毒感染	Syndrome of severe immune failure 严重免疫衰竭综合征
CD4⁺ count 计数	May remain within normal range 可保持正常范围	Usually below 200 cells/µL 通常低于 200 个/µL
Symptoms 症状	May be asymptomatic 可能无症状	Opportunistic infections and cancers 机会性感染和肿瘤

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2. Structure of HIV | HIV 的结构

The HIV particle is approximately 100 nm in diameter. Its outer envelope is derived from the host cell membrane and contains viral glycoproteins gp120 and gp41. Inside, a protein capsid encloses two copies of single-stranded RNA and the enzymes reverse transcriptase, integrase and protease.

HIV 病毒颗粒直径约 100 nm。其外层包膜来自宿主细胞膜，含有病毒糖蛋白 gp120 和 gp41。内部蛋白质衣壳包裹着两条单链 RNA 拷贝以及逆转录酶、整合酶和蛋白酶。

The gp120 glycoprotein binds to the CD4 receptor on host T helper cells, while gp41 facilitates fusion of the viral envelope with the host cell membrane. The viral enzymes are essential for replication.

糖蛋白 gp120 与宿主辅助性 T 细胞表面的 CD4 受体结合，而 gp41 促进病毒包膜与宿主细胞膜融合。这些病毒酶对复制至关重要。

Component 成分	Function 功能
gp120	Binds CD4 receptor on T helper cells 结合辅助性 T 细胞的 CD4 受体
gp41	Mediates membrane fusion 介导膜融合
Reverse transcriptase 逆转录酶	Synthesises DNA from viral RNA 从病毒 RNA 合成 DNA
Integrase 整合酶	Inserts viral DNA into host genome 将病毒 DNA 插入宿主基因组
Protease 蛋白酶	Cleaves viral polyproteins during maturation 在成熟过程中切割病毒多聚蛋白

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3. Transmission of HIV | HIV 的传播途径

HIV is transmitted through direct exchange of infected body fluids, mainly blood, semen, vaginal secretions and breast milk. The main routes are unprotected sexual intercourse, sharing contaminated needles, transfusion of unscreened blood, and mother-to-child transmission during pregnancy, delivery or breastfeeding.

HIV 通过直接交换受感染的体液传播，主要是血液、精液、阴道分泌物和乳汁。主要传播途径为无保护性交、共用污染针具、输入未经筛查的血液，以及妊娠、分娩或哺乳期间的母婴传播。

HIV is not transmitted through casual contact such as shaking hands, sharing utensils, coughing, sneezing, or insect bites. Saliva, tears and urine contain very low amounts of virus and are not considered transmission routes.

HIV 不会通过日常接触传播，如握手、共用餐具、咳嗽、打喷嚏或昆虫叮咬。唾液、泪液和尿液中病毒含量极低，不被视为传播途径。

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4. Replication Cycle of HIV | HIV 的复制周期

HIV replicates inside T helper lymphocytes. The key stages are attachment, fusion, reverse transcription, integration, transcription, translation, assembly and budding.

HIV 在辅助性 T 淋巴细胞内复制。关键阶段包括吸附、融合、逆转录、整合、转录、翻译、组装和出芽。

Step 步骤	Events 事件
Attachment 吸附	gp120 binds CD4 and a co-receptor (CCR5 or CXCR4) on the T helper cell. gp120 结合辅助性 T 细胞上的 CD4 和共受体（CCR5 或 CXCR4）。
Fusion 融合	gp41 fuses viral envelope with host cell membrane; capsid enters cytoplasm. gp41 使病毒包膜与宿主细胞膜融合；衣壳进入细胞质。
Reverse transcription 逆转录	Viral RNA is used as a template to make double-stranded DNA by reverse transcriptase. 逆转录酶以病毒 RNA 为模板合成双链 DNA。
Integration 整合	Viral DNA enters the nucleus; integrase inserts it into host DNA as a provirus. 病毒 DNA 进入细胞核；整合酶将其插入宿主 DNA 形成前病毒。
Transcription 转录	Host RNA polymerase produces viral mRNA from the integrated provirus. 宿主 RNA 聚合酶从整合的前病毒转录出病毒 mRNA。
Translation 翻译	Host ribosomes translate viral mRNA into viral proteins and enzymes. 宿主核糖体将病毒 mRNA 翻译为病毒蛋白质和酶。
Assembly and budding 组装与出芽	New virions assemble and bud from the cell, acquiring an envelope. Protease cleaves polyproteins to make mature infectious particles. 新病毒颗粒组装并从细胞出芽，获得包膜。蛋白酶切割多聚蛋白，形成成熟的感染性颗粒。

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5. Damage to the Immune System | 对免疫系统的损害

HIV mainly infects CD4⁺ T helper lymphocytes because gp120 recognises the CD4 protein on their surface. These cells normally coordinate both cell-mediated and humoral immune responses, so their loss causes severe generalised immunodeficiency.

HIV 主要感染 CD4⁺ 辅助性 T 淋巴细胞，因为 gp120 能识别其表面的 CD4 蛋白。这些细胞通常协调细胞免疫和体液免疫，因此其丧失会导致严重的全身性免疫缺陷。

Infected T helper cells are destroyed directly by viral budding and lysis. In addition, the host immune system may destroy infected and uninfected CD4⁺ cells through cytotoxic T cells and apoptosis. Over time, the CD4⁺ count falls, and the immune system can no longer mount effective responses against pathogens.

被感染的辅助性 T 细胞会因病毒出芽和裂解而被直接破坏。此外，宿主免疫系统可能通过细胞毒性 T 细胞和细胞凋亡破坏感染及未感染的 CD4⁺ 细胞。随着时间推移，CD4⁺ 计数下降，免疫系统无法再对病原体产生有效应答。

Macrophages and dendritic cells can also be infected and act as reservoirs, contributing to persistent infection and viral spread to lymphoid tissues.

巨噬细胞和树突细胞也可能被感染并充当病毒储存库，导致持续感染并促进病毒向淋巴组织扩散。

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6. Clinical Stages and Symptoms | 临床分期与症状

The natural course of untreated HIV infection can be divided into several stages. The first is acute seroconversion illness, which occurs within a few weeks of infection and resembles influenza, with fever, sore throat, rash and lymphadenopathy.

未经治疗的 HIV 感染自然病程可分为若干阶段。首先是急性血清转化期，发生在感染后数周内，类似流感，表现为发热、咽痛、皮疹和淋巴结肿大。

This is followed by a long asymptomatic or clinical latency stage, during which the virus continues to replicate at a low level and CD4⁺ cells gradually decline. The symptomatic stage then appears with persistent swollen lymph nodes, weight loss, chronic diarrhoea and fever.

随后是较长的无症状期或临床潜伏期，病毒继续以低水平复制，CD4⁺ 细胞逐渐减少。之后进入症状期，出现持续性淋巴结肿大、体重下降、慢性腹泻和发热。

Finally, when the CD4⁺ count falls below about 200 cells/µL, the patient develops AIDS. This stage is characterised by opportunistic infections such as Pneumocystis pneumonia, tuberculosis and oesophageal candidiasis, and cancers such as Kaposi’s sarcoma.

最后，当 CD4⁺ 计数降至约 200 个/µL 以下时，患者发展为艾滋病。该阶段以机会性感染为特征，如肺孢子菌肺炎、结核病和食管念珠菌病，以及卡波西肉瘤等肿瘤。

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7. Laboratory Diagnosis | 实验室诊断

HIV infection is most commonly diagnosed by detecting antibodies against viral proteins in the blood. The initial screening test is usually an enzyme-linked immunosorbent assay (ELISA). A positive ELISA result is confirmed by Western blot or a second, different immunoassay to rule out false positives.

HIV 感染最常用的诊断方法是检测血液中针对病毒蛋白的抗体。初筛试验通常为酶联免疫吸附试验（ELISA）。ELISA 阳性结果需通过 Western blot 或第二种不同的免疫测定确证，以排除假阳性。

Rapid tests can detect HIV antibodies or the p24 capsid antigen. Nucleic acid tests detect viral RNA and are useful in early infection. During the window period of about 2 to 8 weeks after infection, antibody tests may still be negative even though the person is infected.

快速检测可检测 HIV 抗体或 p24 衣壳抗原。核酸检测可检出病毒 RNA，在感染早期很有用。在感染后约 2 至 8 周的窗口期内，即使已经感染，抗体检测仍可能为阴性。

Test 检测方法	Detects 检测目标	Notes 说明
ELISA	Anti-HIV antibodies 抗 HIV 抗体	Screening test 初筛试验
Western blot	Antibodies to specific viral proteins 针对特定病毒蛋白的抗体	Confirmation 确证试验
Rapid test 快速检测	Antibodies or p24 antigen 抗体或 p24 抗原	Quick result 结果快速
Nucleic acid test 核酸检测	Viral RNA 病毒 RNA	Early detection 早期检测

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8. Antiretroviral Therapy | 抗逆转录病毒治疗

There is no cure for HIV infection, but combination antiretroviral therapy (ART), also called highly active antiretroviral therapy (HAART), can suppress viral replication for many years. The drugs target different stages of the viral life cycle, including reverse transcriptase, integrase, protease, and viral entry or fusion.

HIV 感染目前无法治愈，但联合抗逆转录病毒治疗（ART），又称高效抗逆转录病毒治疗（HAART），可以多年抑制病毒复制。药物靶向病毒生命周期的不同阶段，包括逆转录酶、整合酶、蛋白酶以及病毒进入或融合过程。

Successful ART reduces the viral load to undetectable levels, allows the CD4⁺ cell count to recover, and prevents progression to AIDS. Strict adherence is essential because HIV has a high mutation rate and can rapidly develop drug resistance if doses are missed.

成功的 ART 可将病毒载量降至检测不到的水平，使 CD4⁺ 细胞计数恢复，并防止进展为 AIDS。严格依从治疗至关重要，因为 HIV 突变率高，若漏服药物可迅速产生耐药性。

Drug target 药物靶点	Example class 示例类别
Reverse transcriptase 逆转录酶	Nucleoside reverse transcriptase inhibitors (NRTIs) 核苷类逆转录酶抑制剂
Integrase 整合酶	Integrase strand transfer inhibitors (INSTIs) 整合酶链转移抑制剂
Protease 蛋白酶	Protease inhibitors (PIs) 蛋白酶抑制剂
Entry/fusion 进入/融合	CCR5 antagonists, fusion inhibitors CCR5 拮抗剂、融合抑制剂

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9. Prevention and Control | 预防与控制

Since there is no vaccine or cure, prevention is the main strategy for controlling the spread of HIV. Condom use during sexual intercourse reduces transmission, and needle exchange programmes reduce risk among people who inject drugs.

由于没有疫苗或治愈方法，预防是控制 HIV 传播的主要策略。性行为中使用安全套可减少传播，针具交换项目可降低注射吸毒者的感染风险。

Screening of donated blood and blood products prevents transfusion-related infections. Treatment of HIV-positive pregnant women with ART greatly reduces mother-to-child transmission. Other measures include voluntary medical male circumcision and pre-exposure prophylaxis (PrEP). Post-exposure prophylaxis (PEP) can reduce infection if started soon after high-risk exposure.

对献血和血液制品进行筛查可防止输血相关感染。对 HIV 阳性孕妇进行 ART 治疗可大幅降低母婴传播。其他措施包括自愿男性包皮环切和暴露前预防（PrEP）。暴露后预防（PEP）在高危暴露后尽早开始可降低感染风险。

Public health education, regular testing and reducing stigma are also essential to improve uptake of prevention and treatment services.

公共卫生教育、定期检测和减少污名化对于提高预防和治疗服务的可及性也至关重要。

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10. Challenges: Vaccine and Cure | 疫苗与治愈的挑战

Developing an effective HIV vaccine is difficult because the envelope glycoproteins, especially gp120, are highly variable. The virus also integrates into the host genome as a provirus, forming latent reservoirs that are

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