Cell culture experiments showed that SARS-CoV-2, which causes COVID-19, limits the release of viral particles that can be inactivated by antibodies, instead staying tucked within cell walls and spreading between cells.

“It’s basically an underground form of transmission,” said lead author Shan-Lu Liu, a virology professor in the Department of Veterinary Biosciences at The Ohio State University and an investigator in the university’s Center for Retrovirus Research.

“SARS-CoV-2 can spread efficiently from cell to cell because there are essentially no blockers from the host immunity. Target cells become donor cells, and it just becomes a wave of spread, as the virus may not get out of the cells.”

Liu and colleagues found other revealing details about SARS-CoV-2: The spike protein on its surface alone enables cell-to-cell transmission, and yet the virus’s primary receptor on target cells — to which the spike binds — is not a necessary part of the cell-to-cell transmission operation. Additionally, they found that neutralizing antibodies are less effective against the virus when it spreads through cells.

The research was published Wednesday (Dec. 22, 2021) in the journal Proceedings of the National Academy of Sciences.

A major point of this study was comparing SARS-CoV-2 to the coronavirus behind the 2003 SARS outbreak, known as SARS-CoV. The findings help explain why while the first outbreak led to much higher fatality rates and lasted only eight months, we’re about to surpass the two-year mark of the current pandemic, with a majority of cases being asymptomatic, Liu said.

The comparison showed that the SARS-CoV that caused SARS in 2003 is more efficient than SARS-CoV-2 at what is called cell-free transmission, when freely floating viral particles infect target cells by binding to a receptor on their surface — but also remain vulnerable to antibodies produced by previous infection and vaccines. SARS-CoV-2, on the other hand, is more efficient at cell-to-cell transmission — which makes it harder to neutralize with antibodies.

The viruses’ differing efficiencies were first demonstrated in experiments using pseudoviruses — a non-infectious viral core decorated with both kinds of coronavirus spike proteins on the surface.

“The spike protein is necessary and sufficient for both SARS-CoV-2 and SARS-CoV cell-to-cell transmission because the only difference in these pseudoviruses were the spike proteins,” said Liu, also a program director of the Viruses and Emerging Pathogens Program in Ohio State’s Infectious Diseases Institute.

Looking more deeply into those differences, the researchers found that SARS-CoV-2 is also more capable than SARS-CoV at initiating fusion with a target cell membrane, another key step in the viral entry process. And that stronger fusion action was associated with the virus’s enhanced cell-to-cell transmission.

Paradoxically, too much cell membrane fusion leads to cell death and can actually interfere with cell-to-cell transmission, Liu also found.

The team then turned to the role of the ACE2 receptor, a protein on cell surfaces that acts as the gateway for entry of the virus that causes COVID-19. The researchers found, unexpectedly, that cells with no or low levels of ACE2 on their surfaces can be penetrated by the virus, enabling robust cell-to-cell transmission.

“There is no perfect correlation between SARS-CoV-2 infection and the level of ACE2,” Liu said. “ACE2 may be needed for initial infection, but once infection is established, the virus may not need ACE2 anymore because it can spread from cell to cell.”

Finally, in experiments testing blood samples from human COVID-19 patients against the authentic SARS-CoV-2 virus, researchers determined that the virus could evade an antibody response through cell-to-cell transmission, but that antibody neutralization of the virus in the cell-free transmission mode was effective.

“We were able to confirm cell-to-cell transmission is not sensitive to inhibition from antibodies from COVID patients or vaccinated individuals,” Liu said. “Cell-to-cell transmission’s resistance to antibody neutralization is probably something we should watch for as SARS-CoV-2 variants continue to emerge, including the most recent, Omicron. In this sense, developing effective antiviral drugs targeting other steps of viral infection is critical.”

There are still many unknowns, including the exact mechanism the virus uses to spread from cell to cell, how that may influence individuals’ responses to viral infection, and whether or not efficient cell-to-cell transmission contributes to the emergence and spread of new variants. Liu’s lab is planning additional studies using the authentic virus and human lung cells to further explore these questions.

This work was supported by grants from the National Institutes of Health and funds from an anonymous private donor to Ohio State.

Ohio State co-authors include Cong Zeng, Jack Evans, Tiffany King, Yi-Min Zheng, Eugene Oltz, Linda Saif and Mark Peeples, also a researcher at Nationwide Children’s Hospital. Sean Whelan of the Washington University School of Medicine also contributed.

While breakthrough infections have increased with the emergence of the delta and omicron variants, the vaccines remain quite effective at preventing hospitalizations and deaths. The success of the new technology has led scientists to try to figure out why mRNA vaccines are so effective and whether the protection they provide is likely to endure as new variants arise.

A new study from researchers at Washington University School of Medicine in St. Louis and St. Jude Children’s Research Hospital shines light on the quality of the immune response triggered by mRNA vaccines. The study shows that the Pfizer vaccine strongly and persistently activates a kind of helper immune cell that assists antibody-producing cells in creating large amounts of increasingly powerful antibodies, and also drives the development of some kinds of immune memory. Known as T follicular helper cells, these cells last for up to six months after vaccination, helping the body crank out better and better antibodies. Once the helper cells decline, long-lived antibody-producing cells and memory B cells help to provide protection against severe disease and death, the researchers said.

Further, many of the T follicular helper cells are activated by a part of the virus that doesn’t seem to pick up mutations, even in the highly mutated omicron variant. The findings, published online Dec. 22, 2021, in the journal Cell, help explain why the Pfizer vaccine elicits such high levels of neutralizing antibodies and suggests that vaccination may help many people continue producing potent antibodies even as the virus changes.

“The longer the T follicular helper cells provide help, the better the antibodies are and the more likely you are to have a good memory response,” said co-corresponding author Philip Mudd, MD, PhD, an assistant professor of emergency medicine at Washington University. “In this study, we found that these T follicular helper cell responses just keep going and going. And what’s more, some of them are responding to one part of the virus’s spike protein that has very little variation in it. With the variants, especially delta and now omicron, we’ve been seeing some breakthrough infections, but the vaccines have held up very nicely in terms of preventing severe disease and death. I think this strong T follicular helper response is part of the reason why the mRNA vaccines continue to be so protective.”

The first antibodies produced in response to an infection or vaccination tend not to be very good. B cells need to go through a kind of boot camp in so-called germinal centers in the lymph nodes before they can produce really powerful antibodies. T follicular helper cells are the drill sergeants of these boot camps. The helper cells provide instruction to the antibody-producing cells on making ever more potent antibodies and encourage those with the best antibodies to multiply and, in some cases, turn into long-lived antibody-producing cells or memory B cells. The longer the germinal centers last, the better and stronger the antibody response.

Earlier this year, Ali Ellebedy, PhD, an associate professor of pathology & immunology, of medicine and of molecular microbiology at Washington University, reported that, nearly four months after people had received the first dose of the Pfizer vaccine, they still had germinal centers in their lymph nodes that were churning out immune cells directed against SARS-CoV-2, the virus that causes COVID-19.

In this latest study, Mudd and co-corresponding authors Ellebedy and Paul Thomas, PhD, of St. Jude, aimed to understand the role of T follicular helper cells in producing such a strong germinal center response. The research team also included co-first authors Anastasia Minervina, PhD, and Mikhail Pogorelyy, PhD, postdoctoral researchers who work with Thomas at St. Jude, and others.

The researchers recruited 15 volunteers who each received two doses of the Pfizer vaccine three weeks apart. The volunteers underwent a procedure to extract germinal centers from their lymph nodes 21 days after the first dose, just before the second dose; then at days 28, 35, 60, 110 and 200 after the initial dose. None of the volunteers had been infected with SARS-CoV-2 at the start of the study. The researchers obtained T follicular helper cells from the lymph nodes and analyzed them.

The researchers now are studying what happens after a booster dose and whether changes to T follicular helper cells could explain why people with compromised immune systems, such as those with HIV infection, do not mount a strong antibody response.

The device, published Dec. 23 in the journal Nature Nanotechnology, could enable scientists to gain more detailed insights into heart disorders and diseases such as arrhythmia (abnormal heart rhythm), heart attack and cardiac fibrosis (stiffening or thickening of heart tissue).

“Studying how an electrical signal propagates between different cells is important to understand the mechanism of cell function and disease,” said first author Yue Gu, who recently received his Ph.D. in materials science and engineering at UC San Diego. “Irregularities in this signal can be a sign of arrhythmia, for example. If the signal cannot propagate correctly from one part of the heart to another, then some part of the heart cannot receive the signal so it cannot contract.”

“With this device, we can zoom in to the cellular level and get a very high resolution picture of what’s going on in the heart; we can see which cells are malfunctioning, which parts are not synchronized with the others, and pinpoint where the signal is weak,” said senior author Sheng Xu, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering. “This information could be used to help inform clinicians and enable them to make better diagnoses.”

The device consists of a 3D array of microscopic field effect transistors, or FETs, that are shaped like sharp pointed tips. These tiny FETs pierce through cell membranes without damaging them and are sensitive enough to detect electrical signals — even very weak ones — directly inside the cells. To evade being seen as a foreign substance and remain inside the cells for long periods of time, the FETs are coated in a phospholipid bilayer. The FETs can monitor signals from multiple cells at the same time. They can even monitor signals at two different sites inside the same cell.

“That’s what makes this device unique,” said Gu. “It can have two FET sensors penetrate inside one cell — with minimal invasiveness — and allow us to see which way a signal propagates and how fast it goes. This detailed information about signal transportation within a single cell has so far been unknown.”

To build the device, the team first fabricated the FETs as 2D shapes, and then bonded select spots of these shapes onto a pre-stretched elastomer sheet. The researchers then loosened the elastomer sheet, causing the device to buckle and the FETs to fold into a 3D structure so that they can penetrate inside cells.

“It’s like a pop-up book,” said Gu. “It starts out as a 2D structure, and with compressive force it pops up at some portions and becomes a 3D structure.”

The team tested the device on heart muscle cell cultures and on cardiac tissues that were engineered in the lab. The experiments involved placing either the cell culture or tissue on top of the device and then monitoring the electrical signals that the FET sensors picked up. By seeing which sensors detected a signal first and then measuring the times it took for other sensors to detect the signal, the team could determine which way the signal traveled and its speed. The researchers were able to do this for signals traveling between neighboring cells, and for the first time, for signals traveling within a single heart muscle cell.

What makes this even more exciting, said Xu, is that this is the first time that scientists have been able to measure intracellular signals in 3D tissue constructs. “So far, only extracellular signals, meaning signals that are outside of the cell membrane, have been measured in these types of tissues. Now, we can actually pick up signals inside the cells that are embedded in the 3D tissue or organoid,” he said.

The team’s experiments led to an interesting observation: signals inside individual heart cells travel almost five times faster than signals between multiple heart cells. Studying these kinds of details could reveal insights on heart abnormalities at the cellular level, said Gu. “Say you’re measuring the signal speed in one cell, and the signal speed between two cells. If there’s a very big difference between these two speeds — that is, if the intercellular speed is much, much smaller than the intracellular speed — then it’s likely that something is wrong at the junction between the cells, possibly due to fibrosis,” he explained.

Biologists could also use this device to study signal transportation between different organelles in a cell, added Gu. A device like this could also be used for testing new drugs and seeing how they affect heart cells and tissues.

The device would also be useful for studying electrical activity inside neurons. This is a direction that the team is looking to explore next. Down the line, the researchers plan to use their device to record electrical activity in real biological tissue in vivo. Xu envisions an implantable device that can be placed on the surface of a beating heart or on the surface of the cortex. But the device is still far from that stage. To get there, the researchers have more work to do including fine-tuning the layout of the FET sensors, optimizing the FET array size and materials, and integrating AI-assisted signal processing algorithms into the device.

Paper: “Three-dimensional transistor arrays for intra- and inter-cellular recording.” Co-authors include Chunfeng Wang, Namheon Kim, Jingxin Zhang, Tsui Min Wang, Jennifer Stowe, Jing Mu, Muyang Lin, Weixin Li, Chonghe Wang, Hua Gong, Yimu Chen, Yusheng Lei, Hongjie Hu, Yang Li, Lin Zhang, Zhenlong Huang, Pooja Banik, Liangfang Zhang and Andrew D. McCulloch, UC San Diego; Rohollah Nasiri, Samad Ahadian and Ali Khademhosseini, Terasaki Institute for Biomedical Innovation; Jinfeng Li and Peter J. Burke, UC Irvine; Leo Huan-Hsuan Hsu, Xiaochuan Dai and Xiaocheng Jiang, Tufts University; Zheyuan Liu, Massachusetts Institute of Technology; and Xingcai Zhang, Harvard University.

This work was supported by the National Institutes of Health (1 R35 GM138250 01).

Their findings were published in the Federation of European Biochemical Societies journal on October 26.

Being allergic to dogs is a common malady and one that is growing worldwide. Over the years, scientists have been able to identify seven different dog allergens — molecules or molecular structures that bind to an antibody and produce an unusually strong immune response that would normally be harmless.

These seven are named Canis familiaris allergens 1 to 7 (Can f 1-7). But while there are seven, just one, Can f 1, is responsible for the majority (50-75 percent) of reactions in people allergic to dogs. It is found in dogs’ tongue tissue, salivary glands, and their skin.

Researchers have yet to identify Can f 1’s IgE epitopes — those specific parts of the antigens that are recognized by the immune system and stimulate or ‘determine’ an immune response (which is why epitopes are also called antigen determinants). More specifically, epitopes are short amino acid sequences making up part of a protein that induces the immune response.

Epitopes bind to a specific antigen receptor on the surface of immune system antibodies, B cells, or T Cells, much like how the shape of a jigsaw puzzle piece fits the specific shape of another puzzle piece. (The part of the receptor that binds to the epitope is in turn called a paratope). Antibodies, also known as immunoglobulin, come in five different classes or isotypes: IgA (for immunoglobulin A), IgD, IgE, IgG, or IgM. The IgE isotype (only found in mammals) plays a key role in allergies and allergic diseases. There is also an IgE epitope that is the puzzle piece that fits the IgE isotype’s paratope.

In recent years, there has been extensive effort at developing epitope-focused vaccines — in this case, a vaccine against dog allergies.

“We want to be able to present small doses of these epitopes to the immune system to train it to deal with them, similar to the principle behind any vaccine,” said Takashi Inui, a specialist in allergy research, professor at Osaka Prefecture University and a lead author of the study. “But we can’t do this without first identifying the Can f 1’s IgE epitope.”

So the researchers used X-ray crystallography (in which the diffraction of x-rays through a material is analyzed to identify its ‘crystal’ structure) to determine the structure of the Can f 1 protein as a whole — the first time this had ever been done.

They found that the protein’s folding pattern is at first glance extremely similar to three other Can f allergens. However, the locations of surface electrical charges were quite different, which in turn suggest a series of ‘residues’ that are good candidates for the IgE epitope.

Using this basic data, further experimental work needs to be performed to narrow the candidates down, but the findings suggest the development of a hypoallergenic vaccine against Can f 1 — a dog-allergy vaccine — is within our grasp.

The production of a ‘hypoallergenic vaccine’ by use of such epitopes would not just be a world-first with respect to dog allergies but is rare with respect to any allergic reaction. If the researchers’ work is indeed used to develop a dog allergy vaccine, the principles behind it could be used much more widely against various allergies.

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Materials provided by Osaka Prefecture University. Note: Content may be edited for style and length.

“Iodine, the same chemical added as a nutrient to table salt, is eating up ozone in dusty air high in the atmosphere,” said Rainer Volkamer, a CIRES Fellow and professor of chemistry at CU Boulder. Volkamer led the team that made precision atmospheric measurements by aircraft over the eastern Pacific Ocean several years ago. The new finding, he said, has implications for not only air quality, but climate, too — iodine chemistry can make greenhouse gases stick around longer and should give us pause to re-think geoengineering schemes involving dust.

“Our understanding of the iodine cycle is incomplete,” Volkamer said. “There are land-based sources and chemistry we didn’t know about, which we must now consider.”

Atmospheric researchers have long been interested in the observation that dusty layers of air are often very low in the air pollutant ozone, which, when concentrated, can damage people’s lungs and even crops. It seemed that some kind of dust-surface chemistry was eating up ozone, but no one had been able to show that happening in laboratory experiments. Others have speculated about this, but there’s been a lot of doubt, said Volkamer. By contrast, lab experiments have long shown that a gaseous form of iodine can gobble up ozone — but there were only hints of a connection between dust and iodine.

There were other tantalizing hints about the process in a dataset from 2012, from a series of aircraft flights offshore Chile and Costa Rica. Dust seen blowing offshore from South America had striking levels of gaseous iodine. Volkamer handed the data to then-CU Boulder graduate student Theodore Koenig, lead author on this study. Koenig describes those data as one in a set of blurry photographs shared by atmospheric chemists around the world. In one image, for example, “iodine seemed to correlate with dust … but not absolutely clearly,” he said. Everywhere, dust seemed to destroy ozone, but why? “Iodine and ozone clearly connect, but there weren’t any ‘photos’ of both with dust,” said Koenig, who is now an air pollution researcher at Peking University in China.

The data from TORERO (the “Tropical Ocean Troposphere Exchange of Reactive Halogens and Oxygenated Hydrocarbons,” a field campaign funded by the National Science Foundation) captured those three characters together, finally, in one image he said, and it was clear that where desert dust contained significant levels of iodine — like dust from the Atacama and Sechura deserts in Chile and Peru — the iodine was quickly transformed into a gaseous form and ozone dropped to very low levels. But how did that dust-based iodine transform? “The mechanism still remains elusive,” Volkamer said. “That’s future work.”

So the picture is another blurry one, Koenig said, but still, the science is sharper than it was. “I have more questions at the end of the project than at the start,” he said. “But they’re better, more specific questions.”

They’re also very important, for anyone interested in the future of the atmosphere, Volkamer said. Iodine’s reactions in the atmosphere are known to play a role in reducing levels of OH, for example, which can increase the lifetime of methane and other greenhouse gases. Perhaps more importantly, various geoengineering ideas involve injecting dust particles high into Earth’s atmosphere, to reflect incoming solar radiation. There, in the stratosphere, ozone is not a pollutant; rather, it forms a critical “ozone layer” that helps shield the planet from incoming radiation.

If iodine from dust was chemically transformed into an ozone-depleting form in the stratosphere, Volkamer said, “well, that’d not be good, as it could delay the recovery of the ozone layer. Let’s avoid adding anthropogenic iodine into the stratosphere!”