S1PR1 and multiple sclerosis: • Elevated S1PR1 expression is linked to the activation of glial cells and the infiltration of immune cells (Liu et al., 2016).• The use of MicroPET imaging, employing the radioligand [(11)C]TZ3321, enables the evaluation of S1PR1 expression in the lumbar spinal cord of rats with EAE (Liu et al., 2016).• Evaluation of four 18F-labeled S1PR1 tracers (18F-TZ43113, 18F-TZ35104, 18F-TZ4877, and 18F-TZ4881) in a rat model of multiple sclerosis (MS) revealed that 18F-TZ4877 exhibited the most favorable profile for assessing S1PR1 expression in the EAE rat model of MS (Liu et al., 2020).