We will also examine the involvement of specific GPI-APs namely the prion protein PrP<sup>C</sup>, the Folate Receptor alpha and the urokinase plasminogen activator receptor in human diseases focusing on neurodegenerative diseases and cancer.
We overview alternative molecular targets, for which dedicated radiopharmaceuticals have been proposed, including receptors (purinergic receptors P2X7, cannabinoid receptors, α7 and α4β2 nicotinic acetylcholine receptors, adenosine 2A receptor, folate receptor β) and enzymes (cyclooxygenase, nitric oxide synthase, matrix metalloproteinase, β-glucuronidase, and enzymes of the kynurenine pathway), with a particular focus on their respective contribution for the understanding of microglial involvement in neurodegenerative diseases.