The human cathelicidin LL-37 inhibits influenza A viruses through a mechanism distinct from that of surfactant protein D or defensins.

LL-37, the only human cathelicidin, is a cationic antimicrobial peptide with antibacterial and antifungal activity. LL-37 is released from neutrophil granules and produced by epithelial cells. It has been implicated in host defence against influenza A virus (IAV) in recent studies.

Hapivirins and diprovirins: novel θ-defensin analogs with potent activity against influenza A virus.

θ-Defensins are cyclic octadecapeptides found in nonhuman primates whose broad antiviral spectrum includes HIV-1, HSV-1, severe acute respiratory syndrome coronavirus, and influenza A virus (IAV). We previously reported that synthetic θ-defensins called retrocyclins can neutralize and aggregate various strains of IAV and increase IAV uptake by neutrophils. This study describes two families of peptides, hapivirins and diprovirins, whose design was inspired by retrocyclins.

Review: Defensins and cathelicidins in lung immunity.

Defensins were first identified in 1985 and are now recognized as part of a large family of antimicrobial peptides, divided into three categories: alpha-, beta-, and -defensins. These defensin classes differ in structure, sites of expression and biological activities. Human alpha-defensins include peptides that are expressed primarily in neutrophils, whereas human beta-defensins are widely expressed in epithelial cells, including those lining the respiratory tract.

Enhancement of antiviral activity of collectin trimers through cross-linking and mutagenesis of the carbohydrate recognition domain.

Surfactant protein D (SP-D) plays important roles in innate defense against respiratory viruses [including influenza A viruses (IAVs)]. Truncated trimers composed of its neck and carbohydrate recognition domains (NCRDs) bind various ligands; however, they have minimal inhibitory activity for IAV. We have sought to find ways to increase the antiviral activity of collectin NCRDs.

Viral aggregating and opsonizing activity in collectin trimers.

Collectins are collagenous lectins present in blood, respiratory lining fluid, and other mucosal secretions that play important roles in innate defense against infection. The collectin, surfactant protein D (SP-D), limits infection by viruses and bacteria in the respiratory tract, eye, and female genital tract. Multimeric SP-D has strong antiviral activity and is a potent viral and bacterial agglutinin and opsonin; however, trimers composed of the neck and carbohydrate recognition domain (hSP-D-NCRD) of SP-D lack these activities.