Nikhil Prasad Fact checked by:Thailand Medical News Team Nov 19, 2024 2 hours, 31 minutes ago
Medical News: Aging and Immune Vulnerability
Aging not only increases susceptibility to severe illnesses but also impacts recovery, especially when viral infections like coronaviruses are involved. Scientists at the University of North Carolina at Charlotte-USA explored why older adults are at higher risk for complications from respiratory viruses and potential long-term brain-related symptoms. Using a mouse model, they uncovered that age diminishes the brain’s immune response, resulting in more severe disease outcomes and cognitive impairments. This
Medical News report highlights how aging disrupts critical immune defenses in the brain, particularly CD8+ T cells.
How Aging Weakens Brain Immunity and Aggravates Coronavirus Impacts
Aged Brains Are More Vulnerable to Infection
The study found that older mice experienced more severe illnesses and higher mortality when infected with a mouse coronavirus model (MHV-A59). While young mice showed mild symptoms and recovered swiftly, aged mice suffered more intense weight loss, prolonged clinical signs, and up to 80% mortality. Importantly, aged mice exhibited significantly higher viral loads in their brains during infections, a phenomenon tied to weakened immune surveillance in the central nervous system (CNS).
This study underscores that aging disrupts the formation of memory CD8+ T cells - essential immune cells responsible for recognizing and fighting viral threats. Unlike their younger counterparts, aged mice failed to retain enough effective T cells in their brains, leaving them more vulnerable to recurring infections.
Key Study Findings: Immune Breakdown in the Aged Brain
-Reduced Effectiveness of T Cells
One of the most critical observations was the reduced effectiveness of CD8+ T cells in aged mice. Although older mice had an increased number of CD8+ T cells in the brain, most of these were nonspecific to the virus. Younger mice retained more antigen-specific T cells, which provided long-lasting protection and rapidly cleared infections. In contrast, aged mice struggled to establish tissue-resident memory (TRM) T cells, a specialized group vital for long-term defense in the brain.
-Aged T Cells Fail to Protect
Using adoptive transfer experiments, researchers observed that even when adult T cells were introduced into aged mice, these cells struggled to function effectively within the aged brain’s environment. This highlights a dual challenge: intrinsic defects in aged T cells and the negative impact of an aging brain environment.
-Secondary Infections Hit Harder
When aged mice were re-exposed to a different but related coronavirus strain (MHV-JHM), their immune systems were slower to react, resulting in more severe weight loss and worsened clinical symptoms compared to young mice. This vulnerability highlights how age-related immune defects amplify the impact of recurring viral infections.
-Cognitive
Impairments in Aged Mice
One of the most alarming findings was the link between infections and cognitive decline. Aged mice infected with the virus showed significant impairments in spatial learning and memory, as assessed using the Barnes maze. The hippocampus, a critical brain region for learning, showed marked neuronal death and reduced neurogenesis in aged animals.
Researchers used TUNEL assays to confirm that infected neurons in the aged hippocampus underwent apoptosis, or programmed cell death. This neuronal loss was more pronounced during secondary infections, further worsening cognitive deficits.
Activated T Cells Contribute to Neuronal Damage
The study also revealed that activated CD8+ T cells can cause collateral damage in the brain. In vitro experiments demonstrated that these T cells induced neuronal apoptosis, even in uninfected neurons, suggesting that their presence in the aged brain might inadvertently harm healthy cells.
Implications for Human Health
While this research utilized a mouse model, the findings provide crucial insights into how aging may exacerbate diseases like long COVID and neurodegenerative conditions in humans. Older individuals recovering from viral infections could experience greater risks of brain inflammation, cognitive decline, and recurrent infections.
Conclusion
This groundbreaking research demonstrates that aging fundamentally alters how the immune system operates in the brain. The inability of aged brains to maintain effective T cell responses or establish protective memory cells leads to severe disease outcomes and lasting cognitive issues. The findings emphasize the need for targeted therapies that enhance immune resilience in older adults, particularly for preventing or mitigating long-term effects of viral infections.
The study findings were published in the peer reviewed journal: Aging Cell (Wiley).
https://onlinelibrary.wiley.com/doi/10.1111/acel.14409
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Medical News.
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