Tonsils may help transmit HIV during oral sex

The tonsils might serve as a passageway through which HIV enters the body, suggests an analysis of cells from the mouth and throat.

Researchers stress that the risk of acquiring HIV through oral sex is far too low to warrant preventive tonsillectomies. But they say the finding might have implications for preventing transmission of the virus from HIV-infected mothers to their children through breastfeeding.

Niki Moutsopoulos at the National Institute of Dental and Craniofacial Research in Bethesda, Maryland, US, and her colleagues examined gum tissues taken from dental patients to make room for dental crowns, and tonsils taken from eight individuals as part of a treatment for sleep apnoea, a breathing disorder. "They were pretty much going to throw them out if I didn't use them for my research," Moutsopoulos says of the tissue samples.

With the help of specially designed antibody molecules, the team was able to determine the level of various proteins within these tissues.

About 12% of the tonsil cells tested positive for the protein CD4, which sits on the surface of immune cells that are particularly vulnerable to infection by the virus. By comparison, less than 4% of the gum cells contained this protein.

Moutsopolous and her teammates also conducted a genetic analysis of the tissue samples, using special probes that bind to specific DNA sequences. This experiment revealed that the CXCR4 gene was 11 times more active in the tonsils than in the gum samples. The gene codes for a protein, also called CXCR4, that also helps HIV infect immune cells.

Condoms protect

The scientists found further evidence that the tonsils are perhaps more susceptible to HIV infection that other oral areas, including the cheek lining and floor of the mouth.

The new findings provide biological data to complement clinical and epidemiological evidence suggesting that HIV can – in exceptional cases – spread through oral sex, according to John Greenspan, director of the AIDS Research Institute at the University of California in San Francisco, US. "It's a further piece of the jigsaw puzzle," he told New Scientist.

But he and others note that while HIV transmission can occur through oral sex, it appears to happen very rarely. Experts have estimated that at most 4 out of every 10,000 oral sex exposures result in infection, compared with 1 out of every 200 to 1000 episodes of genital contact.

For this reason, researchers suggest people should use condoms to protect themselves from acquiring HIV and other sexually transmitted diseases through oral sex. Undergoing a tonsillectomy to remove the tonsils would be too drastic a measure based on current evidence, they add. "I think that would be a stretch," says Moutsopoulos. "We can't go taking out every tissue that HIV could pass through."

Probiotic treatments

She adds, though, that if future studies bear out a link between tonsils and HIV transmission, there could be implications for blocking the spread of the virus from mother to child in parts of the world where infant formula and antiretroviral drugs are in short supply. Scientists have estimated that a child has a 15% chance of acquiring the virus through breastfeeding within the first year of life.

Greenspan notes that some scientists have started investigating whether probiotic treatments – which promote the growth of healthful bacteria – might reduce the transmission of HIV to very young children through the oral cavity and gastrointestinal tract.

Moutsopoulos stresses that the tonsils – which were removed routinely up until the late twentieth century – are now seen as a first line of defence in the immune system, alerting the body to potentially dangerous foreign particles. For this reason, she does not believe there is enough evidence to warrant their removal as part of a prophylactic measure against HIV transmission.

扁桃体可能帮助艾滋病毒在口交中传播

　　一项针对口腔和喉咙处细胞的研究指出，扁桃体可能为艾滋病毒进入人体内提供方便之门。
　　研究员强调，通过口交感染艾滋病毒的风险太低，因此预防性的扁桃体切除术并无必要。但是他们说，这一发现会促使人们做好预防措施，以避免携带艾滋病毒的母亲通过哺乳将病毒传给婴儿。
　　在美国马里兰州贝塞斯达国立牙科和颅面研究所，Niki Moutsopoulos和她的同事们对牙科病人口腔中的牙冠胶状组织进行了研究。研究对象还包括从八个患有睡眠呼吸暂停症的病人身上切除的扁桃体（切除扁桃体是该病症治疗方案的一部分）。“如果不是我要拿来做研究，它们差点就要被扔掉了。” Moutsopoulos在谈起这些组织样本时说。
　　借助专门设计的抗体分子，该小组能够确定这些组织中各种蛋白质的含量。
　　大约有12 ％的扁桃体细胞对CD4蛋白质检测呈阳性，这些位于免疫细胞表面的细胞尤其容易受到艾滋病毒感染。相比之下，只有不到4 ％的胶细胞含有这种蛋白质。
　　利用与特定DNA序列结合的特殊探针，Moutsopolous和她的队友们还对组织样本进行了遗传分析。这个实验表明，趋化因子受体CXCR4基因在扁桃体细胞中比在胶状样本中活跃11倍。该基因编码的一种蛋白质，也被称为趋化因子受体CXCR4 ，同样有助于艾滋病毒感染免疫细胞。

避孕套的保护
　　科学家们进一步证明，比起其他口交部位，如口腔壁、口腔底面，扁桃体也许更容易感染艾滋病毒。
　　美国旧金山加利福尼亚大学艾滋病研究所约翰格林斯潘主任指出，临床和流行病学证据表明，艾滋病毒可以在特殊情况下通过口交传播，这些新发现所提供的生理学数据为这一说法做出了进一步的证据补充。“这是为七巧板添加了一块新的部分。”他告诉《新科学家》 。
　　但他和其他人指出，虽然艾滋病毒可以通过口交传播，但这种传染的发生十分罕见。比起每200到1000次生殖器性接触就可能导致一次感染的几率相比，专家们估计，每一万次口腔性接触中，最多只有4例可能会导致感染。
　　为此，研究人员建议人们在口交时应该使用避孕套，以保护自己免受艾滋病毒和其他性病的感染。他们补充，根据目前的证据，对于预防艾滋病而言，没有必要接受扁桃体切除术。“我认为那太夸张， ”Moutsopoulos表示。“我们不能考虑切除所有艾滋病毒可能侵入的组织。”

益生菌疗法
　　不过，她补充说，如果未来的研究表明了扁桃体与艾滋病感染之间的联系，这可能为世界上婴儿配方奶和抗逆转录病毒药物供应短缺的地方提供母婴阻断的思路。科学家们估计，在出生后的第一年，孩子有15 ％的机会通过母乳喂养感染艾滋病毒。
　　格林斯潘指出，一些科学家已经开始调查益生菌疗法（一种旨在促进健康细菌生长的疗法）是否可减少艾滋病毒通过口腔和消化道向非常年幼的儿童进行传播。
　　Moutsopoulos强调，在二十世纪后期以前，扁桃体通常被摘除，但现在已被视为免疫系统的第一道防线，对有潜在危险的异己分子为身体做出预警。出于这个原因，她不建议用摘除扁桃体的方式来预防艾滋病毒的传播。