In a study conducted by the Weihenstephan Centre of Sciences at Munich Technical University and of the Max Planck Institute for Psychiatry in Munich, the concentrations in plasma of both TNF-α and its soluble receptors p55 and p75 were analyzed in 523 individuals that had never had a depression, in 35 individuals that had suffered from a depression before but not at the time of the study and in 70 in-patients suffering from acute depression, but without any inflammatory diseases. Here, TNF is linked to depressive disorder.