Review Immunomodulatory Role of the Antimicrobial LL-37 Peptide in Autoimmune Diseases and Viral Infections 1,2, , 3, 4 3 Bapi Pahar * y , Stefania Madonna y , Arpita Das , Cristina Albanesi and Giampiero Girolomoni 5 1 Division of Comparative Pathology, Tulane National Primate Research Center, Covington, LA 70433, USA 2 Department of Microbiology and Immunology, Tulane University School of Medicine, New Orleans, LA 70118, USA 3 IDI-IRCCS, Dermopathic Institute of the Immaculate IDI, 00167 Rome, Italy;
[email protected] (S.M.);
[email protected] (C.A.) 4 Division of Microbiology, Tulane National Primate Research Center, Covington, LA 70433, USA;
[email protected] 5 Section of Dermatology, Department of Medicine, University of Verona, 37126 Verona, Italy;
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[email protected] Authors contributed equally. y Received: 4 August 2020; Accepted: 7 September 2020; Published: 10 September 2020 Abstract: Antimicrobial peptides (AMPs) are produced by neutrophils, monocytes, and macrophages, as well as epithelial cells, and are an essential component of innate immunity system against infection, including several viral infections. AMPs, in particular the cathelicidin LL-37, also exert numerous immunomodulatory activities by inducing cytokine production and attracting and regulating the activity of immune cells. AMPs are scarcely expressed in normal skin, but their expression increases when skin is injured by external factors, such as trauma, inflammation, or infection. LL-37 complexed to self-DNA acts as autoantigen in psoriasis and lupus erythematosus (LE), where it also induces production of interferon by plasmocytoid dendritic cells and thus initiates a cascade of autocrine and paracrine processes, leading to a disease state.