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The prospect of gripping a clammy (or, ew, slimy) subway pole isn't exactly savory, especially in cold-and-flu season, when everyone passes around infections like get-well cards. But, provided your immune system is up to snuff (and you can manage to keep your fingers out of your mouth), there's no good reason to avoid skin-on-metal contact.

There could, however, be a very good reason to get plenty of sleep. In a new opinion paper published in the journal Trends in Neurosciences, German scientists at the University of Tuebingen hypothesize that the immune system requires deep sleep to form memories of diseases, a process they present as critical to fending off infections.

While we still don't know exactly why we need sleep, a solid body of research indicates that rest helps preserve and strengthen memories. In this case, we're talking about "psychological" memories — mental imprints of anecdotes and cross streets and perfume from high school. Among other functions, sleep (specifically deep, or slow-wave, sleep) appears to facilitate the process of converting new information and observations into longterm memories. 

In a similar manner, the German research team says, deep sleep also aids the immune system in consolidating memories of previously encountered viruses and bacteria. The basic idea is that the immune system needs to create memories of infections that cross its path in order to recognize and fight off said infections in the future. 

Researchers hypothesize that creating immunological memories works like this: First, the immune system comes into contact with a pathogen (i.e. the bacterial, viral or fungal microorganism that causes disease) and collects enough information about the pathogen to form or "encode" a memory of it. Specifically, the immune system encounters an antigen, the pathogenic molecule targeted in developing an immune response. Encoding hinges on creating "memory T cells," a type of disease-fighting cell. These memory T cells only collect "gist information" — like a Cliff's Notes version of the pathogen — so the immune system will be able to recognize not only identical diseases, but similar diseases, too. 

Then, just as the central nervous system does with psychological memories, the immune system must consolidate the gist information encoded by the memory T cells. And this happens during slow-wave sleep. 

To support their claim, researchers site studies that have shown a link between getting slow-wave sleep the night after vaccination and longterm increases in memory T cells.

"Taken together," the study press release says, "the findings support the view that slow-wave sleep contributes to the formation of long-term memories of abstract, generalized information, which leads to adaptive behavioral and immunological responses."

So, based on this theory, if you come into contact with an infection and don't log that sweet, infection-fighting slow-wave sleep, your immune system might flub the memory-making process, leaving you vulnerable to getting sick from diseaseas against which you'd otherwise have protection.