The common cold virus can reproduce itself more efficiently in the cooler temperatures found inside the nose than at core body temperature, according to a new Yale-led study. This finding may confirm the popular yet contested notion that people are more likely to catch a cold in cool-weather conditions.

Researchers have long known that the most frequent cause of the common cold, the rhinovirus, replicates more readily in the slightly cooler environment of the nasal cavity than in the warmer lungs. However, the focus of prior studies has been on how body temperature influenced the virus as opposed to the immune system, said study senior author and Yale professor of immunobiology Akiko Iwasaki.

To investigate the relationship between temperature and immune response, Iwasaki and an interdisciplinary team of Yale researchers spearheaded by Ellen Foxman, a postdoctoral fellow in Iwasaki's lab, examined the cells taken from the airways of mice. They compared the immune response to rhinovirus when cells were incubated at 37 degrees Celsius, or core body temperature, and at the cooler 33 degrees Celsius. "We found that the innate immune response to the rhinovirus is impaired at the lower body temperature compared to the core body temperature," Iwasaki said.

The study also strongly suggested that the varying temperatures influenced the immune response rather than the virus itself. Researchers observed viral replication in airway cells from mice with genetic deficiencies in the immune system sensors that detect virus and in the antiviral response. They found that with these immune deficiencies, the virus was able to replicate at the higher temperature. "That proves it's not just virus intrinsic, but it's the host's response that's the major contributor," Iwasaki explained.

Although the research was conducted on mouse cells, it offers clues that may benefit people, including the roughly 20% of us who harbor rhinovirus in our noses at any given time. "In general, the lower the temperature, it seems the lower the innate immune response to viruses," noted Iwasaki. In other words, the research may give credence to the old wives' tale that people should keep warm, and even cover their noses, to avoid catching colds.

Yale researchers also hope to apply this insight into how temperature affects immune response to other conditions, such as childhood asthma. While the common cold is no more than a nuisance for many people, it can cause severe breathing problems for children with asthma, noted Foxman. Future research may probe the immune response to rhinovirus-induced asthma.

The study was published in the Proceedings of the National Academy of Sciences.

參考譯文：

千百年來，人體收到寒涼侵襲容易導致感冒是一種常識，直到今天仍是絕大多數人的真理。

醫學上，上世紀70年代發表在新英格蘭醫學雜志上的系列研究認為寒冷與感冒沒有直接相關性，并逐漸成為主流醫學界共識。

但是，這并沒有說服所有人，包括醫學業內人士。因為除了常識之外，寒冷作為一種事件性因素，可以激發人體應激反應，而應激反應下人體免疫反應通常受到抑制。

而且，先前的研究已經確認，引起感冒的最常見病毒，鼻病毒在比人體核心溫度低的鼻腔環境更容易復制。但是，以前的研究的重點是溫度對于病毒的影響，而不是免疫系統。

發表在1月5日美國國家科學院院刊 上一項來自耶魯大學的研究中，研究人員測試了采集自小鼠呼吸道的上皮細胞在不同溫度下針對鼻病毒做出的先天性免疫反應強度，發現細胞在33℃下對鼻病毒免疫反應強度明顯低于人體核心體溫37℃情況下。

研究人員還觀察了免疫感應缺陷小鼠呼吸道上皮細胞抗病毒免疫反應，發現較高的溫度下病毒也可以在這些免疫缺陷細胞內復制。證明，溫度的影響主要不在病毒本身而是宿主的免疫反應。

雖然該實驗室離體細胞研究的結果不一定完全試用于人體，但是畢竟給出這樣一個提示，溫度越低細胞對于病毒先天性免疫應答強度也就越低。

通常情況下，大致有20%的人鼻腔存在可以引發感冒的鼻病毒，這個實驗結果提示，受涼或許可以通過影響人體的免疫反應而更加容易發生感冒的可能性。

耶魯大學的研究人員還希望能夠用這種研究方法深入研究溫度對于其他疾病可能存在的影響，比如兒童哮喘的免疫反應等。

原始來源：http://www.sciencedaily.com/releases/2015/01/150105170014.htm