P4HB and neuroblastoma: The neuron may be another source of brain-derived csPDI, since a recent proteomic analysis of CNS synaptic cleft proteins identified csPDI/P4HB among the most enriched candidates at both excitatory and inhibitory synapses in embryonic rat cortical neuronal cultures Loh et al., 2016; csPDI has also been identified at the surface of both neuroblastoma cells (Xiao et al., 1999) and retinal cells (Pariser et al., 2000).