Inflammation is the sign that our body is defending itself against an aggression. But when this response escalates, for example in the brain, it can lead to serious neurological or psychiatric diseases. A team investigated a marker protein targeted by medical imaging to visualize cerebral inflammation, but whose interpretation was still uncertain. The team reveals that a large quantity of this protein goes hand in hand with a large quantity of inflammatory cells, but its presence is not a sign of their overactivation. These results pave the way for optimal observation of neuroinflammatory processes and a re-reading of previous studies on the subject.