RBP4 and major depressive disorder: In RIS animals only, we detected retinol binding protein 4 RET4 (RBP4 in human) and the band 3 anion transport protein B3AT (SLC4A1, in human).A recent report showed that serum levels of RBP4 were lower in patients with MDD than that in healthy individuals and correlated with the duration of disease, which might be related to the MDD prognosis [52].