Antimicrobial peptide LL-37 and recombinant human mannose-binding lectin express distinct age- and pathogen-specific antimicrobial activity in human newborn cord blood in vitro

Abstract

<ns4:p> <ns4:bold>Background:</ns4:bold> There is a need to prevent and treat infection in newborns. One approach is administration of antimicrobial proteins and peptides (APPs) such as LL-37, a membrane-active cathelicidin antimicrobial peptide, and mannose-binding lectin (MBL), a pattern-recognition protein that binds to microbial surface polysaccharides resulting in opsonization and complement activation. Low plasma/serum levels of LL-37 and of MBL have been correlated with infection and exogenous administration of these agents may enhance host defense. </ns4:p> <ns4:p> <ns4:bold>Methods:</ns4:bold> The antimicrobial activity of LL-37 (15 µg/ml) or rMBL (0.5, 2 and 10 µg/ml) was tested in hirudin-anticoagulated preterm and term human cord blood (N = 12–14) against <ns4:italic>Staphylococcus aureus</ns4:italic> (SA) USA 300 (2x10 <ns4:sup>4</ns4:sup> CFU/ml), <ns4:italic>Staphylococcus epidermis</ns4:italic> (SE) 1457 (2x10 <ns4:sup>4</ns4:sup> CFU/ml) and <ns4:italic>Candida albicans</ns4:italic> (CA) SC5314 (1x10 <ns4:sup>4</ns4:sup> CFU/ml). After incubation (1, 45, or 180 min), CFUs were enumerated by plating blood onto agar plates. Supernatants were collected for measurement of MBL via ELISA. </ns4:p> <ns4:p> <ns4:bold>Results:</ns4:bold> Preterm cord blood demonstrated impaired endogenous killing capacity against SA and SE compared to term blood. Addition of LL-37 strongly enhanced antimicrobial/antifungal activity vs SA, SE and CA in term blood and SE and CA in preterm blood. By contrast, rMBL showed modest fungistatic activity vs CA in a sub-analysis of term newborns with high basal MBL levels. Baseline MBL levels varied within preterm and term cohorts with no correlation to gestational age. In summary, exogenous LL-37 demonstrated significant antimicrobial activity against SA, SE and CA in term and SE and CA in preterm human blood tested <ns4:italic>in vitro</ns4:italic> . rMBL demonstrated modest antifungal activity in term cord blood of individuals with high baseline MBL levels. </ns4:p> <ns4:p> <ns4:bold>Conclusions:</ns4:bold> To the extent that our <ns4:italic>in vitro</ns4:italic> results predict the effects of APPs <ns4:italic>in vivo</ns4:italic> , development of APPs for prevention and treatment of infection should take into account host age as well as the target pathogen. </ns4:p>