Researchers develop technique to track yellow fever virus replication

Infection with a strain of yellow fever virus
Infection with a strain of yellow fever virus (YFD-17D) in mouse liver. The liver of a mouse whose immune cells lack the immune signaling component known as STAT1 shows severe lymphocyte infiltration and inflammation, as well as necrosis, after infection with YFV-17D. Credit: Florian Douam and Alexander Ploss

By Staff, Department of Molecular Biology

Researchers from Princeton University‘s Department of Molecular Biology have developed a new method that can precisely track the replication of yellow fever virus in individual host immune cells. The technique, which is described in a paper published March 14 in the journal Nature Communications, could aid the development of new vaccines against a range of viruses, including Dengue and Zika.

Yellow fever virus (YFV) is a member of the flavivirus family that also includes Dengue and Zika virus. The virus, which is thought to infect a variety of cell types in the body, causes up to 200,000 cases of yellow fever every year, despite the widespread use of a highly effective vaccine. The vaccine consists of a live, attenuated form of the virus called YFV-17D, whose RNA genome is more than 99 percent identical to the virulent strain. This one percent difference in the attenuated virus’ genome may subtly alter interactions with the host immune system so that it induces a protective immune response without causing disease.

To explore how viruses interact with their hosts, and how these processes lead to virulence and disease, Alexander Ploss, assistant professor of molecular biology, and colleagues at Princeton University adapted a technique — called RNA Prime flow — that can detect RNA molecules within individual cells. They used the technique to track the presence of replicating viral particles in various immune cells circulating in the blood of infected mice. Mice are usually resistant to YFV, but Ploss and colleagues found that even the attenuated YFV-17D strain was lethal if the transcription factor STAT1, part of the antiviral interferon signaling pathway, was removed from mouse immune cells. The finding suggests that interferon signaling within immune cells protects mice from YFV, and that species-specific differences in this pathway allow the virus to replicate in humans and certain other primates but not mice.

Accordingly, YFV-17D was able to replicate efficiently in mice whose immune systems had been replaced with human immune cells capable of activating interferon signaling. However, just like humans immunized with the attenuated YFV vaccine, these “humanized” mice didn’t develop disease symptoms when infected with YFV-17D, allowing Ploss and colleagues to study how the attenuated virus interacts with the human immune system. Using their viral RNA flow technique, the researchers determined that the virus can replicate inside certain human immune cell types, including B lymphocytes and natural killer cells, in which the virus has not been detected previously. The researchers found that the panel of human cell types targeted by the virus changes over the course of infection in both the blood and the spleen of the animals, highlighting the distinct dynamics of YFV-17D replication in the human immune system.

The next step, said Florian Douam, a postdoctoral research associate in the Department of Molecular Biology and first author on the study, is to confirm YFV replication in these subsets of immune cells in YFV-infected patients and in recipients of the YFV-17D vaccine. Viral RNA flow now provides the means to perform such analyses, Douam said.

The researchers also plan to study whether the virulent and attenuated strains of yellow fever virus infect different host immune cells. The approach may help explain why some people infected with the virus die while others develop only the mildest of symptoms, as well as which changes in the YFV-17D genome weaken the virus’ ability to cause disease. “This could guide the rational design of vaccines against related pathogens, such as Zika and Dengue virus,” Ploss said.

This work was supported by a grant from the Health Grand Challenge program from Princeton University, the New Jersey Commission on Cancer Research (Grant No. DHFS16PPC007), the Genentech Foundation and Princeton University’s Anthony Evnin ’62 Senior Thesis Fund.

Florian Douam, Gabriela Hrebikova, Yentli E. Soto Albrecht, Julie Sellau, Yael Sharon, Qiang Ding and Alexander Ploss. Single-cell tracking of flavivirus RNA uncovers species-specific interactions with the immune system dictating disease outcome. Nature Communications. 8: 14781. (2017). doi: 10.1038/ncomms14781

Researchers correlate incidences of rheumatoid arthritis and giant cell arteritis with solar cycles (BMJ Open)

Solar storm
Coronal mass ejection hurling plasma from the sun. (Image credit: NASA)

By John Greenwald, Princeton Plasma Physics Laboratory

What began as a chat between husband and wife has evolved into an intriguing scientific discovery. The results, published in May in BMJ (formerly British Medical Journal) Open, show a “highly significant” correlation between periodic solar storms and incidences of rheumatoid arthritis (RA) and giant cell arteritis (GCA), two potentially debilitating autoimmune diseases. The findings by a rare collaboration of physicists and medical researchers suggest a relationship between the solar outbursts and the incidence of these diseases that could lead to preventive measures if a causal link can be established.

RA and GCA are autoimmune conditions in which the body mistakenly attacks its own organs and tissues. RA inflames and swells joints and can cause crippling damage if left untreated. In GCA, the autoimmune disease results in inflammation of the wall of arteries, leading to headaches, jaw pain, vision problems and even blindness in severe cases.

Inspiring this study were conversations between Simon Wing, a Johns Hopkins University physicist and first author of the paper, and his wife, Lisa Rider, deputy unit chief of the Environmental Autoimmunity Group at the National Institute of Environmental Health Sciences in the National Institutes of Health, and a coauthor. Rider spotted data from the Mayo Clinic in Rochester, Minnesota, showing that cases of RA and GCA followed close to 10-year cycles. “That got me curious,” Wing recalled. “Only a few things in nature have a periodicity of about 10-11 years and the solar cycle is one of them.”

Wing teamed with physicist Jay Johnson of the U.S. Department of Energy’s Princeton Plasma Physics Laboratory, a long-time collaborator, to investigate further. When the physicists tracked the incidence of RA and GCA cases compiled by Mayo Clinic researchers, the results suggested “more than a coincidental connection,” said Eric Matteson, chair of the division of rheumatology at the Mayo Clinic, and a coauthor. This work drew upon previous space physics research supported by the DOE Office of Science.

The findings found increased incidents of RA and GCA to be in periodic concert with the cycle of magnetic activity of the sun. During the solar cycle, dramatic changes that can affect space weather near Earth take place in the sun. At the solar maximum, for example, an increased number of outbursts called coronal mass ejections hurl millions of tons of magnetic and electrically charged plasma gas against the Earth’s magnetosphere, the magnetic field that surrounds the planet. This contact whips up geomagnetic disturbances that can disrupt cell phone service, damage satellites and knock out power grids. More importantly, during the declining phase of the solar maximum high-speed streams develop in the solar wind that is made up of plasma that flows from the sun. These streams continuously buffet Earth’s magnetosphere, producing enhanced geomagnetic activity at high Earth latitudes.

The research, which tracked correlations of the diseases with both geomagnetic activity and extreme ultraviolet (EUV) solar radiation, focused on cases recorded in Olmsted County, Minnesota, the home of the Mayo Clinic, over more than five decades. The physicists compared the data with indices of EUV radiation for the years 1950 through 2007 and indices of geomagnetic activity from 1966 through 2007. Included were all 207 cases of GCA and all 1,179 cases of RA occurring in Olmsted County during the periods and collected in a long-term study led by Sherine Gabriel, then of the Mayo Clinic and now dean of the Rutgers Robert Wood Johnson Medical School.

Correlations proved to be strongest between the diseases and geomagnetic activity. GCA incidence — defined as the number of new cases per capita per year in the county — regularly peaked within one year of the most intense geomagnetic activity, while RA incidence fell to a minimum within one year of the least intense activity. Correlations with the EUV indices were seen to be less robust and showed a significantly longer response time.

The findings were consistent with previous studies of the geographic distribution of RA cases in the United States. Such research found a greater incidence of the disease in sections of the country that are more likely to be affected by geomagnetic activity. For example, the heaviest incidence lay along geographic latitudes on the East Coast that were below those on the West Coast. This asymmetry may reflect the fact that high geomagnetic latitudes — areas most subject to geomagnetic activity — swing lower on the East Coast than on the opposite side of the country. While Washington, D.C., lies just 1 degree farther north than San Francisco geographically, for example, the U.S. capital is 7 degrees farther north in terms of geomagnetic latitude.

Although the authors make no claim to a causal explanation for their findings, they identify five characteristics of the disease occurrence that are not obviously explained by any of the currently leading hypotheses. These include the east-west asymmetries of the RA and GCA outbreaks and the periodicities of the incidences in concert with the solar cycle. Among the possible causal pathways the authors consider are reduced production of the hormone melatonin, an anti-inflammatory mediator with immune-enhancing effects, and increased formation of free radicals in susceptible individuals. A study of 142 electrical power workers found that excretion of melatonin — a proxy used to estimate production of the hormone — was reduced by 21 percent on days with increased geomagnetic activity.

Confirming a causal link between outbreaks of RA and GCA and geomagnetic activity would be an important step towards developing strategies for mitigating the impact of the activity on susceptible individuals. These strategies could include relocating to lower latitudes and developing methods to counteract direct causal agents that may be controlled by geomagnetic activity. For now, say the authors, their findings warrant further investigations covering longer time periods, additional locations and other autoimmune diseases.

PPPL, on Princeton University’s Forrestal Campus in Plainsboro, N.J., is devoted to creating new knowledge about the physics of plasmas — ultra-hot, charged gases — and to developing practical solutions for the creation of fusion energy. Results of PPPL research have ranged from a portable nuclear materials detector for anti-terrorist use to universally employed computer codes for analyzing and predicting the outcome of fusion experiments. The Laboratory is managed by the University for the U.S. Department of Energy’s Office of Science, which is the largest single supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit

This work was funded from NIH grants (NIAMS R01 AR046849, NIA R01 AG034676). This research was supported in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences. This work has also benefited from the works funded by NSF grants (ATM-0802715, AGS-1058456, ATM09002730, AGS1203299), NASA grants (NNX13AE12G, NNH09AM53I, NN09AK63I, NNH11AR07I), and DOE contract (DE-AC02-09CH11466).

Read the abstract

Wing, Simon; Rider, Lisa G.; Johnson, Jay R.; Miller, Frederick W.; Matteson, Eric L.; Crowson, Cynthia S.; Gabriel, Sherine E. “Do solar cycles influence giant cell arteritis and rheumatoid arthritis incidence?” BMJ Open, May 2015