Skin barrier dysfunction plays also a key role in CTCL pathogenesis [64,65] Th2 cytokines reduce expression of structural proteins produced by keratinocytes, such as filaggrin (FLG), loricrin (LOR) and involucrin (IVL), along with antimicrobial peptides AMPs and keratin 10, leading to increased skin permeability and predisposing to microbial colonization [13,64,66]. Here, IVL is linked to primary cutaneous T-cell non-Hodgkin lymphoma.