However, the S pathway signaling is mostly activated in response to more severe AIH conditions and is characterized by spinal adenosine 2A and 5-HT7 receptor activation, formation of cyclic adenosine monophosphate (cAMP) and synthesis of an immature TrkB isoform (BDNF-independent) and downstream signaling via the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway [3, 6]. Here, BDNF is linked to autoimmune hepatitis.