Microglia matters: visualizing the immune battle in Parkinson's disease.

Microglia play critical roles in immune defense within the central nervous system (CNS), and microglia-mediated immune changes in the brain are observed in various neurodegenerative diseases, including Parkinson's disease (PD). While PET imaging with a range of radiolabeled ligands has been invaluable for visualizing and quantifying neuroimmune changes in the brains of patients with PD, no PET ligands currently exist that are specific to microglia. In this issue of the JCI, Mills et al. used the PET radioligand [¹¹C]CPPC to image colony stimulating factor 1 receptor (CSF1R), revealing a connection between increased CSF1R expression and microglia-mediated brain immune changes in patients with PD. The study demonstrated that elevated CSF1R expression colocalized with a microglial-specific marker in brain regions vulnerable to PD. Moreover, quantifying CSF1R density with [¹¹C]CPPC-PET imaging in living brains may provide an indicator of motor and cognitive impairments in the early stages of PD. These findings underscore the potential of CSF1R-PET imaging as a microglial-sensitive biomarker of brain immune function in PD.