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Immunology Study Suggests the Appendix Has a Use After All

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The appendix has long had a reputation as a redundant organ with no real function. Doctors often remove it even in mild cases of appendicitis to prevent future infection and rupture, which may not always be necessary. But new research on the way innate lymphoid cells (ILCs) protect against infection in people with compromised immune systems may redeem this misunderstood organ. 

“Our study was to investigate the innate lymphoid cells in the gut [of mice] and how they might contribute to the function and protection of the gut,” Gabrielle Belz, of Melbourne’s Walter and Eliza Hall Institute of Medical Research, tells mental_floss. “At the same time, we were interested to know how different immune cells impacted the different parts of the gut.”

ILCs can be found “underlying all the body’s surfaces, including the skin, the lungs, the gut, and the reproductive tract, and play a very important and broad role in protecting the body from infections and responses to environmental insults,” says Belz.  

Belz’s team worked in collaboration with a team headed by Eric Vivier at the Centre d’Immunologie de Marseille-Luminy, France. Together, they set out to explore how ILC3s (one group of ILCs) function during and after a gut infection—particularly how they altered immune protection.

The study, published in Nature Immunology, found that in mice, gut infections begin in the cecum, a small pouch that is considered to be the beginning of the large intestine, and which contains a large patch of ILC3s near its tip. The team infected mice with the murine pathogen Citrobacter rodentium, which establishes first in the cecum. Then they removed the ILC3s, which caused shrinkage of the cecum and inflammation in the colon. Moreover, they uncovered a “layered contribution” of each of the different types of immune cells in the cecum.

“Thus, surprisingly, altering the balance of immune cells significantly affected what was happening in the cecum, suggesting that a similar effect might occur in humans in the appendix,” Belz says. “This highlights that simply disposing of this organ may not always be in our best interests.” 

While the appendix is not required for digestive functions in humans, Belz tells mental_floss, “It does house symbiotic bacteria proposed by Randal Bollinger and Bill Parker at Duke University to be important for overall gut health, but particularly when we get a gut infection resulting in diarrhea.”

Infections of this kind clear the gut not only of fluids and nutrients but also good bacteria. Their research suggests that those ILCs housed in the appendix may be there as a reserve to repopulate the gut with good bacteria after a gut infection.

ILCs are hardier than other immune cells, and thus vital to fighting bacterial infections in people with compromised immune systems, such as those in cancer treatment; they are some of the few immune cells that can survive chemotherapy. 

Belz says that changing the way the appendix is regarded—from vestigial to integral—may also help prevent unnecessary appendix operations. In non-emergency cases of appendicitis, for instance, non-surgical treatments such as antibiotics “can be used to endeavor to calm the inflammation down in the cecum and appendix,” she says. And a healthy appendix may be helping to keep your gut microbiome balanced: Belz has conducted prior research that shows that diet, particularly leafy green and cruciferous vegetables, may help produce ILCs as well. 

More study can also help understand how ILCs play a role in allergic diseases such as asthma, inflammatory bowel disease, and psoriasis. At the very least, Belz says, “It seems likely that [the appendix] is an integral part of the immune system.”

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The Surprising Reason Why Pen Caps Have Tiny Holes at the Top
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If you’re an avid pen chewer, or even just a diehard fan of writing by hand, you’re probably well acquainted with the small hole that tops off most ballpoint pen caps, particularly those classic Bic Cristal pens. The reason it’s there has nothing to do with pen function, it turns out. As Science Alert recently reported, it’s actually designed to counter human carelessness.

Though it’s arguably unwise—not to mention unhygienic—to chomp or suck on a plastic pen cap all day, plenty of people do it, especially kids. And inevitably, that means some people end up swallowing their pen caps. Companies like Bic know this well—so they make pen caps that won’t impede breathing if they’re accidentally swallowed.

This isn’t only a Bic requirement, though the company’s Cristal pens do have particularly obvious holes. The International Organization for Standardization, a federation that sets industrial standards for 161 countries, requires it. ISO 11540 specifies that if pens must have caps, they should be designed to reduce the risk of asphyxiation if they’re swallowed.

It applies to writing instruments “which in normal or foreseeable circumstances are likely to be used by children up to the age of 14 years.” Fancy fountain pens and other writing instruments that are clearly designed for adult use don’t need to have holes in them, nor do caps that are large enough that you can’t swallow them. Any pen that could conceivably make its way into the hands of a child needs to have an air hole in the cap that provides a minimum flow of 8 liters (about 2 gallons) of air per minute, according to the standard [PDF].

Pen cap inhalation is a real danger, albeit a rare one, especially for primary school kids. A 2012 study [PDF] reported that pen caps account for somewhere between 3 and 8 percent of “foreign body aspiration,” the official term for inhaling something you’re not supposed to. Another study found that of 1280 kids (ages 6 to 14) treated between 1997 and 2007 for foreign body inhalation in Beijing, 34 had inhaled pen caps.

But the standards help keep kids alive. In that Beijing study, none of the 34 kids died, and the caps were successfully removed by doctors. That wasn’t always the case. In the UK, nine children asphyxiated due to swallowing pen caps between 1970 and 1984. After the UK adopted the international standard for air holes in pen caps, the number of deaths dropped precipitously [PDF]. Unfortunately, it’s not foolproof; in 2007, a 13-year-old in the UK died after accidentally swallowing his pen cap.

Even if you can still breathe through that little air hole, getting a smooth plastic pen cap out of your throat is no easy task for doctors. The graspers they normally use to take foreign bodies out of airways don’t always work, as that 2012 case report found, and hospitals sometimes have to employ different tools to get the stubbornly slippery caps out (in that study, they used a catheter that could work through the hole in the cap, then inflated a small balloon at the end of the catheter to pull the cap out). The procedure doesn’t exactly sound pleasant. So maybe resist the urge to put your pen cap in your mouth.

[h/t Science Alert]

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Big Questions
What Causes Sinkholes?
Mark Ralston/AFP/Getty Images
Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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