Stories about: innate immunity

Science seen: A “wheel of death” for bacteria

inflammasome innate immunity

The innate immune system acts like a border patrol for the body, picking up bacteria and other invading pathogens using molecular sensors. One key player is the inflammasome, a multi-protein complex depicted here through cryo-electron microscopy (cryo-EM). Using structural biology tools like cryo-EM and X-ray crystallography, the Wu lab in Boston Children’s Hospital’s Program in Cellular and Molecular Medicine show how protein components come together in inflammasomes to form a “wheel of death” against bacterial infection.

Once they detect an invader, inflammasomes send out signals that trigger infected cells to die using an inflammatory death pathway called pyroptosis. They also call for backup from the adaptive immune system, in the form of inflammation. (Image: Wu laboratory/Liman Zhang)

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Drawing a ring around antiviral immunity

Ubiquitin RIG-I innate antiviral immunity Sun Hur
Ubiquitin (pink ovals) doesn’t just tag proteins for recycling. It also may help keep our antiviral immune response in balance. (Image courtesy: Sun Hur)

If you follow cancer biology, then you’ve probably heard of ubiquitin before. Ubiquitin tags a cell’s damaged or used proteins and guides them to a cellular machine called the proteasome, which breaks them down and recycles their amino acids. Proteasome-blocking drugs like Velcade® that go after that recycling pathway in cancer cells have been very successful at treating two blood cancers—multiple myeloma and mantle cell lymphoma—and may hold promise for other cancers as well.

Less well known, however, is the fact that ubiquitin helps normal, healthy cells raise an alarm when viruses attack. Ubiquitin works with a protein called RIG-I, part of a complex signaling pathway that detects viral RNA and triggers an innate antiviral immune response.

Sun Hur, PhD, a structural biologist in Boston Children’s Hospital’s Program in Cellular and Molecular Medicine, has been studying RIG-I and other members of the innate cellular antiviral response for some time. And in a recent paper in Nature, she provided a structural rationale for how ubiquitin helps RIG-I do its job, and how that might help keep our immune system from getting out of hand.

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The obesity-asthma connection: A link in the innate immune system?

asthmatic airway
Obesity may set off innate immune factors that inflame the lungs.

Both asthma and obesity have surged in recent decades, and a growing body of literature is linking the two conditions. Various explanations have been proposed: One recent study suggests that hormonal factors in obesity may regulate airway diameter; another suggests that obesity activates asthma-related genes.

“Why obesity predisposes a person to asthma has been a real puzzle,” says Dale Umetsu, MD, PhD, who recently researched the problem with Hye Young Kim, PhD, and other colleagues in the Division of Allergy and Immunology at Boston Children’s Hospital. “Our goal was to find the connection between these two problems, which occur in both children and adults, and to explore possible new treatments.”

The team’s research indicates that obesity alters the innate immune system—the body’s first responder to infection—in several ways, resulting in lung inflammation. Published earlier this month in Nature Medicine, their work also suggests a completely new, “druggable” approach to treating patients with obesity-associated asthma, for whom standard asthma drugs often work poorly.

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A picture is worth a thousand words for understating innate immunity

What you’re looking at is one of the key ways in which our immune system recognizes viruses before they cause trouble: by sensing the physical presence of their genes. This image by Sun Hur, PhD, will help us better understand how.

Our immune system has immense powers of observation. It needs to in order to fend off the millions of bacteria, viruses, fungi, you name it, that we get exposed to every day.

I’m not talking about antibodies and T cells—parts of the immune system’s adaptive arm, which is fine-tuned to recognize a specific virus or bacterium. Rather, I’m talking about pattern recognition proteins—biological sensors capable of recognizing features and structures that only bacteria or viruses have. These make up the immune system’s innate arm, which essentially primes the body to attack anything that looks remotely like it doesn’t belong.

For instance, our cells carry sensors that can detect double-stranded RNA (dsRNA), which certain kinds of viruses use to encode their genome—like the rotavirus, which causes severe diarrhea in infants and small children. Our genome, by contrast, is encoded in DNA, and the RNA we make is single-stranded; if there’s dsRNA present, it means there’s a virus around.

In a recent paper in Cell, Sun Hur, PhD, of the Program in Cellular and Molecular Medicine at Boston Children’s Hospital, and one of her postdoctoral fellows, Bin Wu, PhD, spotlight one of our dsRNA pattern recognizers, a protein called MDA5.

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