SYP and major depressive disorder: Accordingly, Kuwano et al. [114] analyzed neuron-derived exosomes (NDE) in the peripheral blood of MDD patients and found that synaptophysin (SYP, a synaptic protein), tumor necrosis factor receptor 1 (TNFR1) and IL-34 (associated with MDD neuroinflammation) were strongly positively correlated with CD81 (EXO surface marker).