Researchers investigating how specialized immune cells called "killer T cells" change throughout a person's life have found that in old age, these cells are replaced by cells with less ability to fight viruses. This world-first discovery improves our understanding of age-related immunity and has the potential to improve vaccines and treatments for different age groups.
Killer T cells (also known as CD8+ or cytotoxic T cells) possess special molecular weapons that can directly attack and destroy other cells infected by foreign invaders such as viruses. Therefore, they play a vital role in the immune system.
There is much research on the role of killer T cells, but less is known about how they evolve and function throughout the life cycle. Now, in a study led by the Peter Doherty Institute for Infection and Immunity and the University of New South Wales Sydney, researchers have looked at differences in killer T cells in newborns, school-age children, adults and adults aged 60 and over to understand how age affects our immunity to influenza viruses.
Carolien van de Sandt, first author of the study, said: "Based on previous research, we expected that killer T cells in older people would become less effective because they were exhausted or 'sleeping'. However, to our surprise, we found that The very effective killer T cells detected in children and adults really seem to disappear in older people and are replaced by suboptimal cells. It's almost like if you replaced a Roman soldier's sword with a kitchen knife, they could learn how to use it, but it would never be as efficient as the sword."
The researchers found that the number of total killer T cells was lowest in newborns, increased in children, and peaked in adulthood. Influenza virus-specific killer T cells are lowest in newborns and children, peak in adults, and decrease in the elderly.
They performed gene expression analysis of cells classified by age and found that influenza-specific killer T cells in newborns and children were genetically similar to those in older adults. However, markers related to maintaining immune control, anti-inflammatory cytokines, and controlling T cell differentiation were highly expressed in adult influenza-specific T cells, less evident in children and the elderly, and absent in neonates.
"One of the most fascinating findings of this study is that these cells with a lower ability to recognize influenza viruses showed very similar genetic signatures to T cells found in newborns," vandeSandt said.
The researchers say their world-first discovery significantly advances our understanding of how immunity changes over the lifespan and could potentially advance the development of vaccines.
"Our results suggest that if we want to boost killer T cells through vaccination, the timing of vaccination may play a critical role in maintaining these optimal killer T cells into old age," said Katherine Kedzierska, the study's corresponding author. "This study is a turning point in research on immunity in the elderly. It has far-reaching implications and opens up new possibilities for developing better vaccines and treatments for different age groups."
The research was published in the journal Nature Immunology.