BDNF and obesity due to melanocortin 4 receptor deficiency: Oxytocin and APP are obesity-specific immune signaling pathways and NK-cell-mediated cytotoxicity, insulin signaling, TCR signaling, ubiquitin-mediated proteolysis, platelet activation BCR signaling, neurotrophin, and oxytocin signaling pathways are T2D immune-system-specific pathways.