Ageing cells dodge immune clearance via PD-L2
The immune system normally clears away damaged and aged cells. But senescent cells in old tissue often linger, even when the body should remove them. New research points to a reason: they express a protein called PD-L2 that tells immune cells to stand down.
Cells that stop dividing and enter a state of senescence release substances that promote chronic inflammation. That is harmful to surrounding tissue. Normally, certain immune cells (such as T cells) ensure that these aged cells are cleared. But in older tissue, this process becomes less effective. The question was: how do senescent cells escape that clearance mechanism?
PD-L2 as an immune shield
The researchers describe that senescent cells in aged tissue express the protein PD-L2. PD-L2 is an inhibitory signal that instructs immune cells not to attack the cell displaying it. This is the same type of inhibitory system that tumours use to escape immune surveillance. By deploying this signal, senescent cells can persist in tissue far longer than is beneficial.
The finding comes from the Fight Aging! newsletter, which references primary research. This is an early-stage observation, and further studies are needed to confirm whether blocking PD-L2 actually improves clearance of senescent cells and whether doing so is safe.
Implications for ageing treatments
If PD-L2 does play a role in shielding senescent cells from immune clearance, it represents a potential target. Drugs that block PD-L2 already exist; they are used in certain cancers. Whether they could be repurposed for ageing is an open question. But the idea that senescent cells actively evade the immune system via a mechanism resembling tumour biology gives the search for effective approaches a new direction.
Search terms to explore further: senescence immune evasion PD-L2, immune checkpoint senescence, inflammaging immune clearance