Brain ischemia, i.e. oxygen deprivation due to lack of blood circulation after a stroke or during childbirth (asphyxia), causes great suffering for patients and their families as well as high costs to society. Brain cells in the ischemic tissue die and their functions are lost. Depending on which area of the brain is affected, this can lead to difficulty in controlling voluntary movements, loss of sensation, language and swallowing difficulties, epilepsy, etc. Obstetric asphyxia with acute brain damage in newborn babies is a major cause of cerebral palsy. There is currently no effective way to repair damaged brain tissue and current research focuses on reducing the damage and improving functional recovery by stimulating the brain's plasticity that underpins our ability to learn and adapt. The complement system is a central part of the innate immune system and is best known for protecting us from dangerous bacteria. However, it also has other important functions, not least in the brain. We have shown that the complement system can protect brain cells against ischemia and stimulate brain plasticity. Our goal is to build on these findings to develop new effective treatments for newborn babies and adults with ischemic brain damage.