Longevity Briefs: A Poor T Cell Output Puts You At Twice The Risk Of Death

Longevity briefs provides a short summary of novel research in biology, medicine, or biotechnology that caught the attention of our researchers in Oxford, due to its potential to improve our health, wellbeing, and longevity.

Why is this research important: The thymus is an organ in which cells of the immune system are ‘trained’ to recognise pathogens and ignore the body’s own cells. As we age, the thymus shrinks in size and the quality and quantity of its immune cell output decreases. The decline of the immune system seems to play an important role in the ageing process, leading to higher levels of inflammation and greater susceptibility to pathogens. A healthy immune system is also needed to keep tissues free of damaged and dysfunctional cells.

What did the researchers do: In this study, researchers measured the thymic output of 241 nursing home residents (aged 78.4 on average) in Southern Italy. They did this by taking blood samples and measuring the presence of a specific type of DNA fragment called an sjTREC. These fragments are by-products of T cells maturing in the thymus – they are produced when developing T cells rearrange parts of the genes that encode T cell receptors (the receptors that recognise pathogenic antigens). This technique has already proven successful for estimating human age in forensic studies. In this study, researchers wanted to see how well it correlated with mortality among participants.

Key takeaway(s) from this research: At the start of the study, lower levels of sjTREC were correlated with older age, suggesting reduced thymic output. However, there was a lot of variation, with plenty of 90+ year-olds having better thymic output than some 70 year-olds. This is in line with previous evidence that both genetic and lifestyle factors play a significant role in the rate of thymic decline.

Poorer thymic function was associated with significantly increased mortality during 3 years of follow-up, irrespective of participants’ age. The 25% of participants with the lowest sjTREC were over twice as likely to die for any reason when compared to participants with a normal sjTREC level for their age. This remained true when controlling for factors like sex, BMI, medication and various medical conditions.

So, this study suggests that poor thymic output is quite a strong predictor of mortality. Since sjTREC is just DNA, it can be measured in any blood sample even if it contains no viable immune cells. This potentially makes it more useful than many other markers of immune function. One straightforward use might be to direct vaccination campaigns by identifying those with the most compromised immune function. Of course, we would ideally like to regenerate the thymus and hopefully rejuvenate the immune system in the process. There are multiple ways in which this could be done, but these would not be enough to reverse immune ageing completely.