APP and psoriasis: Communication between hair follicle cells and keratinocytes was found to be more robust in psoriasis than in normal skin, with entirely different ligand-receptor pairs: DSG1 (Desmoglein 1) / DSC3 (Desmocollin 3) and HBEGF (Heparin Binding EGF Like Growth Factor) / EGFR (Epidermal Growth Factor Receptor) in normal skin, and APP/CD74, COL4A2 (Collagen Type IV Alpha 2 Chain) / CD44 (Cell Surface Glycoprotein CD44), and LAMC1 (Laminin Subunit Gamma 1) /CD44 in psoriasis.