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It is a mystery why humans show huge differences in lifespan, health, and susceptibility to infectious diseases. However, a team of international scientists has found that the ability to fight or recover from infection and inflammation (a trait they call "immune resilience") is one of the main reasons for these differences.
The study's co-author, Weijing He, explained that immune resilience includes controlling inflammation and maintaining or rapidly restoring immune activity at any age. He and his colleagues found that people with the highest immune resilience were more likely to live longer, fight infections and **cancer**, and survive COVID and sepsis.
Measure immune elasticity
The researchers measured immune resilience in two ways. The first is based on the relative number of two types of immune cells, CD4+ T cells and CD8+ T cells. CD4+ T cells coordinate the immune system's response to pathogens and are often used as a measure of immune health (higher levels usually indicate a stronger immune system). However, in 2021, researchers found that low levels of CD8+ T cells (responsible for killing damaged or infected cells) are also important indicators of immune health. In fact, patients with high levels of CD4+ T cells and low levels of CD8+ T cells during SARS-CoV-2 and HIV infections are the least likely to develop severe COVID and AIDS.
In the same study in 2021, the researchers identified a second measure of immune resilience involving two gene expression traits associated with the risk of death in infected individuals. One of the signatures was associated with a higher risk of death;It includes genes associated with inflammation – an important process that activates the immune system but can cause considerable damage if left unchecked. Another characteristic is associated with a greater chance of survival;It includes genes involved in controlling inflammation. These genes help the immune system produce a balanced immune response during infection and gradually reduce the response once the threat is gone. The researchers found that participants who expressed the optimal combination of genes lived longer.
Immune resilience and longevity
The researchers evaluated the level of immune resilience of nearly 50,000 participants of all ages and with various immune system challenges, including acute infection, chronic diseases and cancer. Their assessment suggests that individuals with optimal levels of immune resilience are more likely to live longer, resist HIV and influenza infections, fight off **cancer after kidney transplantation**, and defend against covid infection and sepsis.
However, a person's immune resilience fluctuates all the time. Study participants with optimal immune resilience prior to common symptomatic viral infections such as colds or flu experienced a shift in gene expression to poor immune resilience within 48 hours of symptom onset. As these people recover from the infection, many gradually return to previously more favorable levels of gene expression. However, nearly 30% of people who once had optimal immune resilience did not fully regain survival-related traits at the end of cold and flu season, even if they had recovered from the disease.
This may indicate that the stages vary from person to person and disease to disease. For example, young female sex workers have a lot of clients and are not using *** and are therefore repeatedly exposed to sexually transmitted pathogens – they have very low immune recovery. However, over the next 10 years, most sex workers began to reduce their chances of exposure to sexually transmitted pathogens by using *** and reducing the number of sexual partners, and their immune recovery capacity improved.
Immune elasticity and aging
The researchers found that the proportion of people with the best immune resilience tended to be highest among younger adults and lowest among older people. Researchers believe that as people age, they are exposed to a growing number of health conditions (acute infections, chronic diseases, cancer, etc.) that challenge their immune system to go through a "response-recovery" cycle. During the response phase, CD8+ T cell and inflammatory gene expression increases, and during the recovery phase, they decrease again.
However, over the course of a lifetime of repeated challenges, the immune system recovers more slowly, altering a person's immune resilience. Interestingly, some people over the age of 90 still have optimal immune resilience, suggesting that these people's immune systems have a special ability to control inflammation and quickly restore proper immune balance, despite the many reactions and recovery cycles that their immune systems face.
The impact on public health can be significant. Immune cell and gene expression profiling assessments are relatively straightforward, and being able to determine a person's ability to recover immunity can help determine if a person is at greater risk of developing the disease, how well they respond, and whether, and to what extent.