Your immune system鈥檚 ability to combat COVID-19, like any infection, largely depends on its ability to replicate the immune cells effective at destroying the SARS-CoV-2 virus that causes the disease. These cloned immune cells cannot be infinitely created, and a key hypothesis of a new 91探花 study is that the body鈥檚 ability to create these cloned cells falls off significantly in old age.

According to a model created by 91探花research professor , this genetically predetermined limit on your immune system may be the key to why COVID-19 has such a devastating effect on the elderly. Anderson is the lead author of a paper detailing this modeled link between aging, COVID-19 and mortality.

鈥淲hen DNA split in cell division, the end cap 鈥� called a telomere 鈥� gets a little shorter with each division,鈥� explains Anderson, who is a modeler of biological systems in the School of Aquatic and Fishery Sciences. 鈥淎fter a series of replications of a cell, it gets too short and stops further division. Not all cells or all animals have this limit, but immune cells in humans have this cell life.鈥�

The average person鈥檚 immune system coasts along pretty good despite this limit until about 50 years old. That鈥檚 when enough core immune cells, called T cells, have shortened telomeres and cannot quickly clone themselves through cellular division in big enough numbers to attack and clear the COVID-19 virus, which has the trait of sharply reducing immune cell numbers, Anderson said. Importantly, he added, telomere lengths are inherited from your parents. Consequently, there are some differences in these lengths between people at every age as well as how old a person becomes before these lengths are mostly used up.

Anderson said the key difference between this understanding of aging, which has a threshold for when your immune system has run out of collective telomere length, and the idea that we all age consistently over time is the 鈥渕ost exciting鈥� discovery of his research.

鈥淒epending on your parents and very little on how you live, your longevity or, as our paper claims, your response to COVID-19 is a function of who you were when you were born,鈥� he said, 鈥渨hich is kind of a big deal.鈥�

To build this model the researchers used publicly available data on COVID-19 mortality from the Center for Disease Control and US Census Bureau and studies on telomeres, many of which were published by the co-authors over the past two decades.

Assembling telomere length information about a person or specific demographic, he said, could help doctors know who was less susceptible. And then they could allocate resources, such as booster shots, according to which populations and individuals may be more susceptible to COVID-19.

鈥淚鈥檓 a modeler and see things through mathematical equations that I am interpreting by working with biologists, but the biologists need to look at the information through the model to guide their research questions,鈥� Anderson said, admitting that 鈥渢he dream of a modeler is to be able to actually influence the great biologists into thinking like modelers. That鈥檚 more difficult.鈥�

One caution Anderson has about this model is that it might explain too much.

鈥淭here鈥檚 a lot of data supporting every parameter of the model and there is a nice logical train of thought for how you get from the data to the model,鈥� he said of the model鈥檚 power. 鈥淏ut it is so simple and so intuitively appealing that we should be suspicious of it too. As a scientist, my hope is that we begin to understand further the immune system and population responses as a part of natural selection.鈥�

Co-authors include Ezra Susser, Mailman School of Public Health, Columbia University; Konstantin Arbeev and Anatoliy Yashin, Social Science Research Institute, Duke University; Daniel Levy, National Heart, Lung, and Blood Institute, National Institutes of Health; Simon Verhulst, University of Groningen, Netherlands; Abraham Aviv, New Jersey Medical School, Rutgers University.

###

For more information, contact Anderson at jjand@uw.edu.

Twins not only have a bestie from birth 鈥� they also live longer than singletons. And those two factors may be related, according to new 91探花 research.

While twins have been subjects in countless studies that try to separate the effects of nature from nurture, a recent in PLOS ONE is the first to actually look at what being a twin means for life expectancy. Analysis shows that twins have lower mortality rates for both sexes throughout their lifetimes.

“We find that at nearly every age, identical twins survive at higher proportions than fraternal twins, and fraternal twins are a little higher than the general population,” said lead author , a 91探花postdoctoral researcher in aquatic and fishery sciences.

The results suggest a significant health benefit for close social connections.

The data comes from the , one of the oldest repositories of information about twins. The authors looked at 2,932 pairs of same-sex twins who survived past the age of 10 who were born in Denmark between 1870 and 1900, so all subjects had completed their lifespan. They then compared their ages at death with data for the overall Danish population.

For men, they found that the peak benefit of having a twin came in the subjects’ mid-40s. That difference is about 6 percentage points, meaning that if out of 100 boys in the general population, 84 were still alive at age 45, then for twins that number was 90. For women, the peak mortality advantage came in their early 60s, and the difference was about 10 percentage points.

The authors believe their results reflect the benefits of social support, similar to the . Many studies have suggested that being married acts as a social safety net that provides psychological and health perks.

But one question surrounding the so-called marriage protection hypothesis, Sharrow said, is whether marriage really makes you healthier, or whether healthier people are just more likely to get married (or join a community group or have a large circle of friends, which also are tied to better health).

“Looking at twins removes that effect, because people can’t choose to be a twin,” Sharrow said. “Our results lend support to a big body of literature that shows that social relationships are beneficial to health outcomes.”

A social network can boost health in many ways, he said. Friends can provide healthy outlets and activities, and encourage you to give up bad habits. Just having a shoulder to cry on, a caregiver during an illness, or a friend to vent with can be healthy over the long term.

“There is benefit to having someone who is socially close to you who is looking out for you,” Sharrow said. “They may provide material or emotional support that lead to better longevity outcomes.”

Sharrow is a statistician who specializes in demographics and mortality. He and co-author , a 91探花research professor in aquatic and fishery sciences and an affiliate of the 91探花Center for Studies in Demography and Ecology, were looking to tune a mortality model using the data from twins. But when they ran the numbers they stumbled upon an unexpected discovery.

Their model separates acute causes of death, such as accidents or behavior-related causes, from natural causes in old age. Female twins only had lower mortality for the earlier, acute causes. Male twins got a bigger overall longevity boost than women because they had lower mortality rates both for acute causes during their early years and from so-called natural causes past the age of 65. Sharrow believes these reflect the immediate and cumulative effects of male twins making healthier choices.

“Males may partake in more risky behaviors, so men may have more room to benefit from having a protective other 鈥� in this case a twin 鈥� who can pull them away for those behaviors,” Sharrow said.

The lifespan was also extended more for identical rather than fraternal twins, which may reflect the strength of the social bond.

“There is some evidence that identical twins are actually closer than fraternal twins,” Sharrow said. “If they’re even more similar, they may be better able to predict the needs of their twin and care for them.”

The authors would like to make sure that the findings are replicated in other datasets, to ensure that it’s not just that Danish twins who survived past the age of 10 in the 19^th century had other advantages that had the effect of extending their lifespan.

If the findings hold up, they have implications far beyond twins.

“Research shows that these kinds of social interactions, or social bonds, are important in lots of settings,” Sharrow said. “Most people may not have a twin, but as a society we may choose to invest in social bonds as a way to promote health and longevity.”

The study was funded by the National Institutes of Health’s National Institute on Aging.

###

For more information, contact Sharrow at 206-543-7848 or dsharrow@uw.edu.

Grant #: R21AG046760-01