Researchers found that a short piece of the antimicrobial peptide LL‑37, specifically the C‑terminal 22‑amino‑acid segment (called P6), can block RSV virus replication in lab‑grown cells without causing the inflammation that the full‑length peptide does. This suggests a more focused peptide might be useful as an antiviral, though it’s still early‑stage research.

To investigate the core functional region of antimicrobial peptide LL-37, which inhibites RSV replication and could be developed for theraputic aplication. A panel of 6 partial LL-37 peptides (referred to as P1 to P6) was synthesized according to LL-37 amino acide sequence. Hep-2 cells were infected with RSV, treated with LL-37 or partial peptides respectively. Cells were collected after 24 hours incubation at 37 degrees C, CO2 5%. Total RNA was obtained from the cells. Expression level of RSV N gene was quantified by real-time PCR. Meanwhile enzyme-linked immunosorbent assay (ELISA) was used to quantify the chemokines RANTES, IL-8, MCP1 in the supernatants of Hep-2 cultures after 24 h incubation with or without LL-37 and partial peptide P6. N-terminal partial LL-37 peptide (corresponding to residues 1-12 of LL-37) had no significant effects on RSV replication (P > 0.05). In contrast, C-terminal (corresponding to residues 13-37) and a panel of 4 overlapping 22-mer partial peptides (from the peptide incorporating aa 13-34 through that spanning aa 16-37) showed significant inhibitory effect on RSV replication to some extent (P < 0.05 or P < 0.01). LL-37 induced significant expression of chemokine RANTES, IL-8 and MCP-1 in Hep-2 cells. In contrast, partial peptide P6 had no significant effect on expression of the chemokines in Hep-2 cells. The LL-37 C-terminal 22-mer partial peptide P6 was putative core functional region for inhibition of RSV replication. The partial peptide didn't induce significant expression of chemokine RANTES, IL-8 and MCP-1.