RIGI and melanoma: The PRRs, expressed by epithelial cells and innate immune cells, are classified into several families: retinoic acid–inducible gene I (RIG-I)–like receptors (RLRs) [including RIG-I and melanoma differentiation-associated protein 5 (MDA5)], Toll-like receptors (TLRs), nucleotide-binding oligomerization domain (NOD)–like receptors (NLRs), the cyclic GMP-AMP synthase (cGAS), absent in melanoma 2–like receptors, and C-type lectin receptors (18).