A new look at immune ageing

The thymus is the organ in which all T cells, a key white blood cell in our immune system, develop. The thymus shrinks with age, degenerating from a plump milky organ (just above the heart) to a ratty-looking fat-riddled vestige which barely produces any new T cells. This degeneration means that older persons are producing fewer and fewer T cells, contributing to the poor responses to vaccines and infections with age. Despite the importance of this process, there is a great debate in immunology over why the thymus gets worse with age, with some scientists pointing out the structural degeneration of the thymus itself, while others suggest that it is instead due to poorer function of the bone-marrow that sends stem cells to the thymus to be turned into T cells.

In a new study from the Autoimmune Genetics Laboratory, published in the European Journal of Immunology, we use a range of imaging and genetic techniques to address this key question. We undoubtly find the structural degeneration in the organ with age, but by comparing two mouse strains that have a thymus ageing at different rates, we find that the structural abnormalities do not actually limit production of T cells. Instead, it is the reduced function of the bone-marrow that leads to a reduction in new T cells. These results suggest that researchers looking into immune ageing direct their attention towards the bone-marrow, where rescuing stem cell production may allow even older persons to produce fresh T cells for a healthy life.

Data from Franckaert et al, European Journal of Immunology. The C57BL/6 mouse (top) has a thymus that ages slowly, while the FVB/N mouse (bottom) has a thymus that ages rapidly.