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These Oddball Cells May Explain How Influenza Leads to Asthma

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Cells of a mouse lung after an H1N1 infection
Credit: Andrew Vaughan, University of Pennsylvania, Philadelphia

Most people who get the flu bounce right back in a week or two. But, for others, the respiratory infection is the beginning of lasting asthma-like symptoms. Though I had a flu shot, I had a pretty bad respiratory illness last fall, and since that time I’ve had exercise-induced asthma that has occasionally required an inhaler for treatment. What’s going on? An NIH-funded team now has evidence from mouse studies that such long-term consequences stem in part from a surprising source: previously unknown lung cells closely resembling those found in taste buds.

The image above shows the lungs of a mouse after a severe case of H1N1 influenza infection, a common type of seasonal flu. Notice the oddball cells (green) known as solitary chemosensory cells (SCCs). Those little-known cells display the very same chemical-sensing surface proteins found on the tongue, where they allow us to sense bitterness. What makes these images so interesting is, prior to infection, the healthy mouse lungs had no SCCs.

SCCs, sometimes called “tuft cells” or “brush cells” or “type II taste receptor cells”, were first described in the 1920s when a scientist noticed unusual looking cells in the intestinal lining [1] Over the years, such cells turned up in the epithelial linings of many parts of the body, including the pancreas, gallbladder, and nasal passages. Only much more recently did scientists realize that those cells were all essentially the same cell type. Owing to their sensory abilities, these epithelial cells act as a kind of lookout for signs of infection or injury.

This latest work on SCCs, published recently in the American Journal of Physiology–Lung Cellular and Molecular Physiology, adds to this understanding. It comes from a research team led by Andrew Vaughan, University of Pennsylvania School of Veterinary Medicine, Philadelphia [2].

As a post-doc, Vaughan and colleagues had discovered a new class of cells, called lineage-negative epithelial progenitors, that are involved in abnormal remodeling and regrowth of lung tissue after a serious respiratory infection [3]. Upon closer inspection, they noticed that the remodeling of lung tissue post-infection often was accompanied by sustained inflammation. What they didn’t know was why.

The team, including Noam Cohen of Penn’s Perelman School of Medicine and De’Broski Herbert, also of Penn Vet, noticed signs of an inflammatory immune response several weeks after an influenza infection. Such a response in other parts of the body is often associated with allergies and asthma. All were known to involve SCCs, and this begged the question: were SCCs also present in the lungs?

Further work showed not only were SCCs present in the lungs post-infection, they were interspersed across the tissue lining. When the researchers exposed the animals’ lungs to bitter compounds, the activated SCCs multiplied and triggered acute inflammation.

Vaughan’s team also found out something pretty cool. The SCCs arise from the very same lineage of epithelial progenitor cells that Vaughan had discovered as a post-doc. These progenitor cells produce cells involved in remodeling and repair of lung tissue after a serious lung infection.

Of course, mice aren’t people. The researchers now plan to look in human lung samples to confirm the presence of these cells following respiratory infections.

If confirmed, the new findings might help to explain why kids who acquire severe respiratory infections early in life are at greater risk of developing asthma. They suggest that treatments designed to control these SCCs might help to treat or perhaps even prevent lifelong respiratory problems. The hope is that ultimately it will help to keep more people breathing easier after a severe bout with the flu.

References:

[1] Closing in on a century-old mystery, scientists are figuring out what the body’s ‘tuft cells’ do. Leslie M. Science. 2019 Mar 28.

[2] Development of solitary chemosensory cells in the distal lung after severe influenza injury. Rane CK, Jackson SR, Pastore CF, Zhao G, Weiner AI, Patel NN, Herbert DR, Cohen NA, Vaughan AE. Am J Physiol Lung Cell Mol Physiol. 2019 Mar 25.

[3] Lineage-negative progenitors mobilize to regenerate lung epithelium after major injury. Vaughan AE, Brumwell AN, Xi Y, Gotts JE, Brownfield DG, Treutlein B, Tan K, Tan V, Liu FC, Looney MR, Matthay MA, Rock JR, Chapman HA. Nature. 2015 Jan 29;517(7536):621-625.

Links:

Asthma (National Heart, Lung, and Blood Institute/NIH)

Influenza (National Institute of Allergy and Infectious Diseases/NIH)

Vaughan Lab (University of Pennsylvania, Philadelphia)

Cohen Lab (University of Pennsylvania, Philadelphia)

Herbert Lab (University of Pennsylvania, Philadelphia)

NIH Support: National Heart, Lung, and Blood Institute; National Institute on Deafness and Other Communication Disorders


Can Childhood Stress Affect the Immune System?

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Katie Ehrlich

Katie Ehrlich
Credit: Alan Flurry, University of Georgia, Athens

Whether it’s growing up in gut-wrenching poverty, dealing with dysfunctional family dynamics, or coping with persistent bullying in school, extreme adversity can shatter a child’s sense of emotional well-being. But does it also place kids at higher of developing heart disease, diabetes, and other chronic health conditions as adults?

Katherine Ehrlich, a researcher at University of Georgia, Athens, wants to take a closer look at this question. She recently received a 2018 NIH Director’s New Innovator Award to study whether acute or chronic psychosocial stress during childhood might sensitize the body’s immune system to behave in ways that damage health, possibly over the course of a lifetime.


Looking to Llamas for New Ways to Fight the Flu

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Lllama nanobodiesResearchers are making tremendous strides toward developing better ways to reduce our risk of getting the flu. And one of the latest ideas for foiling the flu—a “gene mist” that could be sprayed into the nose—comes from a most surprising source: llamas.

Like humans and many other creatures, these fuzzy South American relatives of the camel produce immune molecules, called antibodies, in their blood when exposed to viruses and other foreign substances. Researchers speculated that because the llama’s antibodies are so much smaller than human antibodies, they might be easier to use therapeutically in fending off a wide range of flu viruses. This idea is now being leveraged to design a new type of gene therapy that may someday provide humans with broader protection against the flu [1].


Creative Minds: Does Human Immunity Change with the Seasons?

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Micaela Martinez

Micaela Martinez

It’s an inescapable conclusion from the book of Ecclesiastes that’s become part of popular culture thanks to folk legends Pete Seeger and The Byrds: “To everything (turn, turn, turn), there is a season.” That’s certainly true of viral outbreaks, from the flu-causing influenza virus peaking each year in the winter to polio outbreaks often rising in the summer. What fascinates Micaela Martinez is, while those seasonal patterns of infection have been recognized for decades, nobody really knows why they occur.

Martinez, an infectious disease ecologist at Princeton University, Princeton, NJ, thinks colder weather conditions and the tendency for humans to stay together indoors in winter surely play a role. But she also thinks an important part of the answer might be found in a place most hadn’t thought to look: seasonal changes in the human immune system. Martinez recently received an NIH Director’s 2016 Early Independence Award to explore fluctuations in the body’s biological rhythms over the course of the year and their potential influence on our health.


Birth Year Predicts Bird Flu Risk

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Incidence of Avian Flu vs. Year of Birth

Caption: Birth years of people in China who contracted H7N9 avian flu from 1997-2015 (left); birth years of people in Cambodia, China, Egypt, Indonesia, Thailand, and Vietnam who contracted H5N1 avian flu from 1997-2015 (right).
Source: Adapted from Science. 2016 Nov 11;354(6313):722-726.

You probably can’t remember the first time you came down with the flu as a kid. But new evidence indicates that the human immune system never forgets its first encounters with an influenza virus, possibly even using that immunological “memory” to protect against future infections by novel strains of avian influenza, or bird flu.

In a study that looked at cases of bird flu in six countries in Asia and the Middle East between 1997 and 2015, an NIH-supported research team found that people born before 1968 were at lower risk of becoming seriously ill or dying from the H5N1 strain of the bird flu virus than were those born afterwards [1]. Just the opposite was true of another emerging strain of bird flu. People born before 1968 were at greater risk of becoming seriously ill or dying of H7N9, while those born after that date were more often protected.


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