TSPO and schizophrenia: While in vivo PET neuroimaging has the advantage of allowing longitudinal study of the dynamics of glial activation, inconsistent results among cross-sectional PET studies have raised questions about the validity of the TSPO tracer as biomarker and the potential role of immunosenescence and symptomatic state on microglial activity in schizophrenia (Boche et al., 2019, Conen et al., 2020, De Picker et al., 2019b, Plavén-Sigray et al., 2020, Sneeboer et al., 2020).