• Young blood and old mice restore organ functions and prolong life.

• Clinical trials of a drug for the treatment of Alzheimer’s disease are underway.

• Platelet factor 4 (PF4) acts as an intermediary between the brain and the immune system.

• PF4 suppresses inflammation and supports cognitive functions of the brain at a young age.

• PF4 levels decrease with age, causing inflammation and impeding neuronal communication.

• PF4 injection partially restores the immune system and improves cognition in older mice.

• PF4 may be part of an overall rejuvenation strategy, but aging affects each person individually.