The Human Cathelicidin LL-37, a Defensive Peptide Against Rotavirus Infection

Abstract

LL-37 is a 37 amino acid long cationic peptide belonging to the cathelicidin family of antimicrobial peptides. Limited investigations have shown the antimicrobial potency of LL-37 against different viral infections. We aimed to investigate the effect of the human cathelicidin peptide LL-37 on rotavirus infection, as a causative agent of severe gastroenteritis in children. After evaluation of LL-37 toxicity using methyl thiazolyl tetrazolium and neutral red uptake assays on the MA-104 cells, antiviral activity was assessed both by tissue culture infectious dose 50 (TCID50) and quantitative Real-Time PCR assays. Indirect immunofluorescence assay (IFA) and hematoxylin and eosin (H&E) staining were also performed to further confirm the inhibitory effects of the LL-37 on rotavirus. The viability maintained more than 90% up to the concentration of 50 μg/mL of peptide. LL-37 exerted its antiviral effect only when cells were pre-treated with peptide prior to rotavirus infection. 50 μg/mL of LL-37 could result in 3.36 log10 TCID50 reduction in virus titer (p = 0.0001), and an inhibition rate of 82.2% in copy number of rotavirus genomic RNA was obtained. IFA showed that the expression of rotavirus antigens in cells pre-treated with 50 μg/mL LL-37 is noticeably lower than the virus control. H&E assay also showed that the size and formation of inclusion bodies are decreased in rotavirus-infected cells pre-treated with 50 μg/mL LL-37 as compared to the virus control. Our findings suggested that the LL-37 peptide may interfere with viral attachment or act as an immune regulator, promoting innate immune responses.