頻繁的性行爲讓女性的免疫系統做好受孕準備

For decades, doctors have recom that couples trying to conceive should have intercourse as often as possible, not only during ovulation (obviously) but at other times as well. Doing so is known to improve the odds of success, though the reasons have remained a puzzle. Now two new studies suggest, somewhat radically, that sex alters a woman’s immune system in ways that affect her chances of conceiving.

數十年來，醫生會向試圖懷孕的伴侶建議，儘可能頻繁地性交，不僅是在排卵期（顯然），其他時間也一樣。大家都知道這樣做可以增加成功機率，不過其中的原因卻一直是個謎。現在，有兩項新研究頗具重大意義地顯示出，性活動會改變女性的免疫系統，從而影響她的受孕機率。

The data for the studies come from the Kinsey Institute for Research on Sex, Gender and Reproduction and the Center for the Integrative Study of Animal Behavior, both at Indiana University, where researchers recruited 30 healthy, premenopausal women, all of whom were heterosexual and not trying to become pregnant. About half of them were sexually active, using condoms or intrauterine devices as birth control, while the others were abstinent. The volunteers provided blood, saliva and other samples throughout several menstrual cycles. Apart from their sex lives, women in both groups were broadly similar in terms of health and lifestyle.

這兩項研究的數據分別出自金賽性、性別與生殖研究所(Kinsey Institute for Research on Sex, Gender and Reproduction)和動物行爲綜合研究中心(Center for the Integrative Study of Animal Behavior)。兩家機構均設在印第安納大學(Indiana University)。研究人員招募了30名更年期之前的健康女性，全部爲異性戀，而且並未嘗試懷孕。其中大約一半人性生活活躍，採用安全套或宮內節育器避孕，另一半人則禁慾。志願受試人員提供了數個月經週期的血液和唾液等樣本。除了性生活方面的差異，兩組女性在健康狀況和生活方式方面大致相似。

They soon revealed distinctly different immune-system responses over the course of a menstrual cycle. According to one of the new studies, published in September in the journal Fertility and Sterility, the sexually active women displayed heightened levels of a certain immune cell when their reproductive systems were preparing to release an egg but before they were able to become pregnant. Later in the menstrual cycle, when conception was possible, these women developed higher levels of a different type of immune cell — one known to help a body recognize and ignore nonhazardous foreign cells, like those in a fetus. There were no similar changes in the immune systems of the abstinent women.

他們很快發現，在一個月經週期內，兩組女性的免疫系統反應截然不同。其中一項發表於《生育和不育》(Fertility and Sterility)雜誌9月刊的研究顯示，在女性的生殖系統正準備排卵但還無法受孕之前，性生活活躍的女性某類免疫細胞的水平會比較高。在月經週期後期，也就是有可能懷孕時，這些女性體內又有另一種不同類型的免疫細胞的水平會升高——這種免疫細胞有助於人體辨認和忽視無害的外來細胞，比如來自胎兒的細胞。禁慾女性的體內沒有類似的免疫系統變化。

The other study, published in Physiology and Behavior, found other immunological differences. Sexually active women early in their cycles developed more antibodies of a type that lives in the mucus lining the reproductive tract and represents a threat to sperm and fetuses. Levels of these antibodies dropped later in the cycle, while the numbers of a different germ-fighting antibody in the blood but not in the reproductive tract grew.

發表在《生理學與行爲》(Physiology and Behavior)雜誌上的另一項研究發現了一些其他的免疫系統差別。在月經週期早期，性生活活躍的女性體內某種抗體水平比較高。該抗體存在於生殖道粘膜內，對精子和胎兒都構成威脅。在月經週期後期，這種抗體的水平會下降，另一種不同的抗菌抗體的數量則會增多。這種抗體存在於血液裏，而不存於生殖道中。

Together, these findings indicate that ‘‘the more frequently a woman engages in sexual activity, the more often her immune system gets the message that it’s time to reproduce,’’ says Tierney Lorenz, the research scientist at the Kinsey Institute who was the lead author of both studies. The research did not examine conception or rates of illness and infection, so the real-life implications of the differences in immunity remain uncertain. It’s also not clear how the immune system knows someone is having sex. There may be messages from the brain or extra changes in hormones, Lorenz says. Sexual partners may even exchange elements of their microbiome, prompting changes in each other’s immunity. For now, the primary lesson Lorenz takes away from these studies, she says, is ‘‘awe for the elegance of our flexible, powerful, socially aware immune system.’’

這些發現共同顯示出，“女性性生活越頻繁，她的免疫系統就會更頻繁地接到信號，提示是進行繁殖的時候，”在金賽性、性別與生殖研究所做研究的科學家、上述兩項研究的第一作者蒂爾尼·洛倫茨(Tierney Lorenz)說。這項研究沒有調查受孕情況，也沒有研究患病和感染的機率，所以不同的免疫狀況在真實生活中會有什麼影響仍未可知。同樣還不清楚的是，免疫系統如何知道某人在做愛。洛倫茨表示，有可能是大腦發送了信號，或者有荷爾蒙的額外變化進行提示。性伴侶甚至可能會交換體內的菌羣，由此引發對方體內的免疫系統發生變化。洛倫茨表示，她目前從這兩項研究中得到的最大收穫，是“對我們那靈活、強大和具備外界感知力的免疫系統的精妙，產生了敬畏之心。”

This column appears in the October 25, 2015 issue of The New York Times Magazine

原文將刊登在2015年10月25日出版的一期《紐約時報雜誌》上。