Salk scientists identify how immune cells use two critical receptors to clear dead cells from the body, pointing the way to new autoimmune and cancer therapies
In most of the tissues of the body, specialized immune cells are entrusted with the task of engulfing the billions of dead cells that are generated every day. When these garbage disposals don't do their job, dead cells and their waste products rapidly pile up, destroying healthy tissue and leading to autoimmune diseases such as lupus and rheumatoid arthritis.
Now, Salk scientists have discovered how two critical receptors on these garbage-eating cells identify and engulf dead cells in very different environments, as detailed today in Nature Immunology.
"To target these receptors as treatments for autoimmune disease and cancer, it's important to know exactly which receptor is doing what. And this discovery tells us that," says senior author of the work Greg Lemke, Salk professor of molecular neurobiology and the holder of Salk's Françoise Gilot-Salk Chair.
The garbage-disposing cells, known as macrophages, have arrays of receptors on their surface, two of which—called Mer and Axl—are responsible for recognizing dead cells in normal environments and inflamed environments, respectively. Mer operates as a "steady-as-she-goes" receptor, clearing out dead cells in healthy tissues on a daily basis. Axl, in contrast, acts as an "all-hands-on-deck" receptor, kicking macrophages into action in inflammatory settings that result from infection or tissue trauma. These inflamed environments have many more dead cells.
"We thought Axl and Mer were doing the same job, and they are: they both recognize a so-called 'eat me' signal displayed on the surface of dead cells. But it turns out that they work in very different settings," says Lemke, whose lab first discovered the two receptors—which, along with a third, make up the TAM family—two decades ago. Lemke and colleagues explored the roles of TAM receptors in the brain initially, but observed that the absence of these receptors had dramatic effects on the immune system, including the development of autoimmune disease.
The receptors have since become a growing focus for cancer and autoimmune research, and previous work has found that these three receptors are important in other areas, including the intestines, reproductive organs and vision.
"This basic research focus allowed us to discover a completely new aspect of immune regulation that no one—including any immunologist—had known about before," adds Lemke.
In the new work, the researchers found multiple critical differences between Axl and Mer. For example, the receptors use different molecules—called ligands—to be activated: Axl has a single such ligand and, once engaged, is quickly cleaved off of the surface of the macrophage. Levels of the free-floating Axl in the blood have turned out to be an accurate, general biomarker for inflammation, quickly showing up in the circulation after tissue trauma or injury.
"We compared the behavior and regulation of the receptors, and the results were very striking," says first author Anna Zagórska. "In response to many different pro-inflammatory stimuli, Axl was upregulated and Mer was not. In contrast, immunosuppressive corticosteroids, which are widely used to suppress inflammation in people, upregulated Mer and suppressed Axl. These differences were our entry point to the study."
Next, the researchers are looking into each receptor's activity in more detail. The team is finding that these receptors are unusual in that they have a three-step binding procedure, whereas most cell receptors bind in one step. Exploring and understanding this process will help to lead to more targeted therapeutics for cancers and other diseases in which the receptors are thought to act.
Authors on the paper include Anna Zagórska, Paqui Través, Erin Lew, Ian Dransfield and Greg Lemke.
The work was funded by the National Institutes of Health, the Leona M. and Harry B. Helmsley Charitable Trust, the Nomis Foundation, the H.N. and Frances C. Berger Foundation, the Fritz B. Burns Foundation, the HKT Foundation, the Human Frontiers Science Program, and the Leukemia and Lymphoma Society.
About the Salk Institute for Biological Studies
The Salk Institute for Biological Studies is one of the world's preeminent basic research institutions, where internationally renowned faculty probes fundamental life science questions in a unique, collaborative, and creative environment. Focused both on discovery and on mentoring future generations of researchers, Salk scientists make groundbreaking contributions to our understanding of cancer, aging, Alzheimer's, diabetes and infectious diseases by studying neuroscience, genetics, cell and plant biology, and related disciplines.
Faculty achievements have been recognized with numerous honors, including Nobel Prizes and memberships in the National Academy of Sciences. Founded in 1960 by polio vaccine pioneer Jonas Salk, MD, the Institute is an independent nonprofit organization and architectural landmark.
Salk Communications | Eurek Alert!
Could this protein protect people against coronary artery disease?
17.11.2017 | University of North Carolina Health Care
Microbial resident enables beetles to feed on a leafy diet
17.11.2017 | Max-Planck-Institut für chemische Ökologie
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses