Posted on by Lawrence Tabak, D.D.S., Ph.D.
Do you feel as if you or perhaps your family members are constantly coming down with illnesses that drag on longer than they should? Or, maybe you’re one of those lucky people who rarely becomes ill and, if you do, recovers faster than others.
It’s clear that some people generally are more susceptible to infectious illnesses, while others manage to stay healthier or bounce back more quickly, sometimes even into old age. Why is this? A new study from an NIH-supported team has an intriguing answer . The difference, they suggest, may be explained in part by a new measure of immunity they call immune resilience—the ability of the immune system to rapidly launch attacks that defend effectively against infectious invaders and respond appropriately to other types of inflammatory stressors, including aging or other health conditions, and then quickly recover, while keeping potentially damaging inflammation under wraps.
The findings in the journal Nature Communications come from an international team led by Sunil Ahuja, University of Texas Health Science Center and the Department of Veterans Affairs Center for Personalized Medicine, both in San Antonio. To understand the role of immune resilience and its effect on longevity and health outcomes, the researchers looked at multiple other studies including healthy individuals and those with a range of health conditions that challenged their immune systems.
By looking at multiple studies in varied infectious and other contexts, they hoped to find clues as to why some people remain healthier even in the face of varied inflammatory stressors, ranging from mild to more severe. But to understand how immune resilience influences health outcomes, they first needed a way to measure or grade this immune attribute.
The researchers developed two methods for measuring immune resilience. The first metric, a laboratory test called immune health grades (IHGs), is a four-tier grading system that calculates the balance between infection-fighting CD8+ and CD4+ T-cells. IHG-I denotes the best balance tracking the highest level of resilience, and IHG-IV denotes the worst balance tracking the lowest level of immune resilience. An imbalance between the levels of these T cell types is observed in many people as they age, when they get sick, and in people with autoimmune diseases and other conditions.
The researchers also developed a second metric that looks for two patterns of expression of a select set of genes. One pattern associated with survival and the other with death. The survival-associated pattern is primarily related to immune competence, or the immune system’s ability to function swiftly and restore activities that encourage disease resistance. The mortality-associated genes are closely related to inflammation, a process through which the immune system eliminates pathogens and begins the healing process but that also underlies many disease states.
Their studies have shown that high expression of the survival-associated genes and lower expression of mortality-associated genes indicate optimal immune resilience, correlating with a longer lifespan. The opposite pattern indicates poor resilience and a greater risk of premature death. When both sets of genes are either low or high at the same time, immune resilience and mortality risks are more moderate.
In the newly reported study initiated in 2014, Ahuja and his colleagues set out to assess immune resilience in a collection of about 48,500 people, with or without various acute, repetitive, or chronic challenges to their immune systems. In an earlier study, the researchers showed that this novel way to measure immune status and resilience predicted hospitalization and mortality during acute COVID-19 across a wide age spectrum .
The investigators have analyzed stored blood samples and publicly available data representing people, many of whom were healthy volunteers, who had enrolled in different studies conducted in Africa, Europe, and North America. Volunteers ranged in age from 9 to 103 years. They also evaluated participants in the Framingham Heart Study, a long-term effort to identify common factors and characteristics that contribute to cardiovascular disease.
To examine people with a wide range of health challenges and associated stresses on their immune systems, the team also included participants who had influenza or COVID-19, and people living with HIV. They also included kidney transplant recipients, people with lifestyle factors that put them at high risk for sexually transmitted infections, and people who’d had sepsis, a condition in which the body has an extreme and life-threatening response following an infection.
The question in all these contexts was the same: How well did the two metrics of immune resilience predict an individual’s health outcomes and lifespan? The short answer is that immune resilience, longevity, and better health outcomes tracked together well. Those with metrics indicating optimal immune resilience generally had better health outcomes and lived longer than those who had lower scores on the immunity grading scale. Indeed, those with optimal immune resilience were more likely to:
- Live longer,
- Resist HIV infection or the progression from HIV to AIDS,
- Resist symptomatic influenza,
- Resist a recurrence of skin cancer after a kidney transplant,
- Survive COVID-19, and
- Survive sepsis.
The study also revealed other interesting findings. While immune resilience generally declines with age, some people maintain higher levels of immune resilience as they get older for reasons that aren’t yet known, according to the researchers. Some people also maintain higher levels of immune resilience despite the presence of inflammatory stress to their immune systems such as during HIV infection or acute COVID-19. People of all ages can show high or low immune resilience. The study also found that higher immune resilience is more common in females than it is in males.
The findings suggest that there is a lot more to learn about why people differ in their ability to preserve optimal immune resilience. With further research, it may be possible to develop treatments or other methods to encourage or restore immune resilience as a way of improving general health, according to the study team.
The researchers suggest it’s possible that one day checkups of a person’s immune resilience could help us to understand and predict an individual’s health status and risk for a wide range of health conditions. It could also help to identify those individuals who may be at a higher risk of poor outcomes when they do get sick and may need more aggressive treatment. Researchers may also consider immune resilience when designing vaccine clinical trials.
A more thorough understanding of immune resilience and discovery of ways to improve it may help to address important health disparities linked to differences in race, ethnicity, geography, and other factors. We know that healthy eating, exercising, and taking precautions to avoid getting sick foster good health and longevity; in the future, perhaps we’ll also consider how our immune resilience measures up and take steps to achieve or maintain a healthier, more balanced, immunity status.
 Immune resilience despite inflammatory stress promotes longevity and favorable health outcomes including resistance to infection. Ahuja SK, Manoharan MS, Lee GC, McKinnon LR, Meunier JA, Steri M, Harper N, Fiorillo E, Smith AM, Restrepo MI, Branum AP, Bottomley MJ, Orrù V, Jimenez F, Carrillo A, Pandranki L, Winter CA, Winter LA, Gaitan AA, Moreira AG, Walter EA, Silvestri G, King CL, Zheng YT, Zheng HY, Kimani J, Blake Ball T, Plummer FA, Fowke KR, Harden PN, Wood KJ, Ferris MT, Lund JM, Heise MT, Garrett N, Canady KR, Abdool Karim SS, Little SJ, Gianella S, Smith DM, Letendre S, Richman DD, Cucca F, Trinh H, Sanchez-Reilly S, Hecht JM, Cadena Zuluaga JA, Anzueto A, Pugh JA; South Texas Veterans Health Care System COVID-19 team; Agan BK, Root-Bernstein R, Clark RA, Okulicz JF, He W. Nat Commun. 2023 Jun 13;14(1):3286. doi: 10.1038/s41467-023-38238-6. PMID: 37311745.
 Immunologic resilience and COVID-19 survival advantage. Lee GC, Restrepo MI, Harper N, Manoharan MS, Smith AM, Meunier JA, Sanchez-Reilly S, Ehsan A, Branum AP, Winter C, Winter L, Jimenez F, Pandranki L, Carrillo A, Perez GL, Anzueto A, Trinh H, Lee M, Hecht JM, Martinez-Vargas C, Sehgal RT, Cadena J, Walter EA, Oakman K, Benavides R, Pugh JA; South Texas Veterans Health Care System COVID-19 Team; Letendre S, Steri M, Orrù V, Fiorillo E, Cucca F, Moreira AG, Zhang N, Leadbetter E, Agan BK, Richman DD, He W, Clark RA, Okulicz JF, Ahuja SK. J Allergy Clin Immunol. 2021 Nov;148(5):1176-1191. doi: 10.1016/j.jaci.2021.08.021. Epub 2021 Sep 8. PMID: 34508765; PMCID: PMC8425719.
COVID-19 Research (NIH)
HIV Info (NIH)
Sepsis (National Institute of General Medical Sciences/NIH)
Sunil Ahuja (University of Texas Health Science Center, San Antonio)
Framingham Heart Study (National Heart, Lung, and Blood Institute/NIH)
“A Secret to Health and Long Life? Immune Resilience, NIAID Grantees Report,” NIAID Now Blog, June 13, 2023
NIH Support: National Institute of Allergy and Infectious Diseases; National Institute on Aging; National Institute of Mental Health; National Institute of General Medical Sciences; National Heart, Lung, and Blood Institute
Posted on by Gary Gibbons, M.D., National Heart, Lung, and Blood Institute; Walter Koroshetz, M.D., National Institute of Neurological Disorders and Stroke; Hugh Auchincloss, M.D., National Institute of Allergy and Infectious Diseases
“I connected with RECOVER to be a part of the answers that I was looking for when I was at my worst.” Long COVID patient and RECOVER representative, Nitza Rochez (Bronx, NY)
People, like Nitza Rochez, who are living with Long COVID—the wide-ranging health issues that can follow an infection with SARS-CoV-2, the coronavirus that causes COVID-19—experience disabling symptoms with significant physical, emotional and financial consequences.
The NIH has been engaging and listening to Nitza and others living with Long COVID even before the start of its Researching COVID to Enhance Recovery (RECOVER) Initiative. But now, with the launch of RECOVER, patients and those with affected family or community members have joined researchers, clinicians, and experts in their efforts to unlock the mysteries of Long COVID. All have come together to understand what causes the condition, identify who is most at risk, and determine how to prevent and treat it.
RECOVER is unprecedented in its size and scope as the most-diverse, deeply characterized cohort of Long COVID patients. We’ve enlisted the help of many patient volunteers, who have enrolled in observational studies designed to help researchers learn as much as possible about people who have Long COVID.
Indeed, thousands of research participants are now providing health information and undergoing in-depth medical evaluations and tests, enabling investigators to look for trends. Additionally, studies of millions of electronic medical records are providing insights about those who have received care during the pandemic. More than 40 studies are being conducted to identify the causes of disease, potential biomarkers of Long COVID, and new therapeutic targets.
In all, RECOVER’s research assets are voluminous. They involve invaluable contributions from many people and communities, including research volunteers, research investigators, and clinical specialists. In addition, millions of health records and numerous related tissues and specimens are being analyzed for possible leads.
At the center of it all is the National Community Engagement Group (NCEG). The NCEG is comprised of people living with Long COVID and those representing others living with the condition, and it is truly instrumental to the initiative’s progress in understanding how and why SARS-CoV-2 impacts people in different ways. It’s also helping researchers learn why some people recover while others do not.
So far, we’ve learned that people hospitalized with COVID-19 are twice as likely to have Long COVID than those who were not hospitalized for infection. We’ve also learned that members of racial and ethnic minority groups with Long COVID were more likely to have been hospitalized with COVID-19.
Similarly, disparities in Long COVID exist within those living in areas with particular environmental exposures , and those who were already burdened by other diseases and conditions—such as diabetes and chronic pulmonary disease . We’ve also discovered that the certain types of symptoms of Long COVID are consistent among patients regardless of which SARS-CoV-2 variant caused their initial infection. Yet, people infected with the earlier variants have a higher number of symptoms than those infected with more recent variants.
Patient experiences have guided and will continue to guide the study designs and trajectory of RECOVER. Now, fueled by the knowledge that we have gained, RECOVER is preparing to advance to the next phase of discovery—testing interventions in clinical trials to see if they can help people with Long COVID.
To prepare, we are beginning to identify potential clinical trial sites. This important step will help us to find the right places with the right staff and capabilities for enrolling the appropriate patient populations needed to implement the studies. We’ll ensure that the public knows when these upcoming clinical trials are ready to enroll.
Of course, the design of these RECOVER clinical trials will be critical, and insights gained from patients have been key in this process. Results from RECOVER study questionnaires, surveys, and discussions with people experiencing Long COVID identified symptom clusters considered to be the most significant and burdensome to patients. These include sleep disorders, “brain fog” (trouble thinking clearly), exercise intolerance and fatigue, and nervous system dysfunction affecting people’s ability to regulate normal body functions like heart rate and body temperature.
These patient observations have effectively guided the design of the clinical trials that will evaluate whether certain interventions and therapies can help alleviate symptoms that are part of these specific clusters. We’re excited to be advancing toward this phase of the initiative and, again, are very grateful to patient representatives like Nitza, quoted above, for getting us to this phase.
Effective evaluation of those treatments will be important, too. Early in the pandemic, while many clinical trials were launching, most were not large enough or did not have the appropriate objectives to define effective treatments for acute COVID-19. This left clinicians with few clear options when faced with patients needing help.
Learning from this experience, the RECOVER trials will be harmonized to ensure coordinated and efficient evaluation of interventions—in other words, all potential therapies will be using the same protocols platforms and the same data elements. This consistency accelerates our understanding and strengthens the certainty of findings.
Given the widespread and diverse impact that the virus has on the body, it is highly likely that more than one treatment will be needed for each kind of patient experience. Finding solutions for everyone—people of all races, ethnicities, genders, ages, and geographic locations—is paramount.
RECOVER patient representative, Juan Lewis, of San Antonio shared with us, “In April 2020, I was fighting for my life, and today I fight for my quality of life. COVID impacted me physically, mentally, socially, and financially.”
For people like Juan who are experiencing debilitating Long COVID symptoms, we know that finding answers as quickly as possible is critical. As we look ahead to the next 12 months, we’ll continue the studies evaluating the underlying causes, risk factors, and outcomes of Long Covid, and we anticipate significant scientific progress on research leading to Long COVID treatments.
Keep an eye on the RECOVER website for updates on our progress, and published findings.
 Identifying environmental risk factors for post-acute sequelae of SARS-CoV-2 infection: An EHR-based cohort study from the recover program. Zhang Y, Hu H, Fokaidis V, V CL, Xu J, Zang C, Xu Z, Wang F, Koropsak M, Bian J, Hall J, Rothman RL, Shenkman EA, Wei WQ, Weiner MG, Carton TW, Kaushal R. Environ Adv. 2023 Apr;11:100352.
 Identifying who has long COVID in the USA: a machine learning approach using N3C data. Pfaff ER, Girvin AT, Bennett TD, Bhatia A, Brooks IM, Deer RR, Dekermanjian JP, Jolley SE, Kahn MG, Kostka K, McMurry JA, Moffitt R, Walden A, Chute CG, Haendel MA; N3C Consortium. Lancet Digit Health. 2022 Jul;4(7):e532-e541.
NIH Builds Large Nationwide Study Population of Tens of Thousands to Support Research on Long-Term Effects of COVID-19, NIH News Release, September 15, 2021
Understanding Long-Term COVID-19 Symptoms and Enhancing Recovery, NIH Director’s Blog, October 4, 2022.
NIH RECOVER Research Identifies Potential Long COVID Disparities. NIH News Release, February 16, 2023.
NIH RECOVER Listening Session, June 2021 (NIH Videocast)
NIH RECOVER Listening Session: Understanding Long COVID Across Communities of Color and Those Hardest Hit by COVID, January 21, 2022 (NIH Videocast)
Note: Dr. Lawrence Tabak, who performs the duties of the NIH Director, has asked the heads of NIH’s Institutes, Centers, and Offices to contribute occasional guest posts to the blog to highlight some of the interesting science that they support and conduct. This is the 25th in the series of NIH guest posts that will run until a new permanent NIH director is in place.