LL37 Inhibits Aspergillus fumigatus Infection via Directly Binding to the Fungus and Preventing Excessive Inflammation

Abstract

The incidence of Aspergillus fumigatus infection and the rate of resistance to antifungal drugs have sharply increased in recent years. LL37 has been reported as a host defense peptide with broad-spectrum antibacterial activities. However, the role of LL37 during A. fumigatus infection remains unclear. Here, we examined the interaction between LL37 and A. fumigatus and found that synthetic LL37 could directly bind to the surface of A. fumigatus , disrupting the integrity of the cell wall in vitro . LL37 inhibited mycelial growth in a concentration-dependent manner, rather than fungicidal effect even at high concentration (e.g., 20 μM). Interestingly, low concentrations of LL37 (e.g., 4 μM) significantly attenuated mycelial adhesion and prevented the invasion and destruction of epithelial cells. Following LL37 treatment, the levels of proinflammatory cytokines released by A. fumigatus -stimulated macrophages decreased significantly, accompanied by downregulation of M1 type markers. In a mouse model of pulmonary A. fumigatus infection, LL37-treated mice showed lower amounts of fungi load, moderate pathological damage, and reduced proinflammatory cytokines. Further, LL37 transgenic mice (LL37+/+) were examined to investigate the effects of endogenous LL37 in an A. fumigatus infection model and showed lower susceptibility to A. fumigatus infection in comparison with wild-type mice. In addition, LL37 also played a protective role in an immunosuppressed mouse model of A. fumigatus infection. Thus, LL37 inhibits A. fumigatus infection via directly binding to mycelia and reducing excessive inflammation. LL37 or its analogs may therefore constitute potential drug components for A. fumigatus infection.

Antifungal Activity of Antimicrobial Peptides and Proteins against Aspergillus fumigatus

“…Recently, 1 µM LL-37 has been reported to promote the growth of A. fumigatus when grown in Sabouraud dextrose broth for 24 and 48 h [12]. In contrast with this, another recent study reported that 1-20 µM LL-37 inhibits mycelial growth of A. fumigatus in a dose-dependent manner when grown in RPMI for 12 h [13]. These contrasting observations are not easily explained, although differences between strains, AMP concentrations and experimental conditions probably account for these contrasting results.…”

“…AMPs are key components of the human defences against invading microorganisms. Over 100 human AMPs have been described, ranging in size from 10 to 149 amino acids, and have net charges Histones 5-150 µg/mL [29,30] Inhibitory activity against Candida albicans reported at 26 µg/mL [34] LL-37 0.5-10 nM [25][26][27][28] Inhibitory activity against A. fumigatus at 20 µM [15] and growth promotion activity against A. fumigatus at 1 µM [12,13] lactoferrin 1-10 µM [18][19][20][21][22] Inhibitory activity against C. albicans at 0.25-2.5 µM [35] β-defensin-1 0.2-2 nM [6,23] Inhibitory activity against C. albicans at 7 µM [36] This study aimed to characterise the anti-Aspergillus activity of these AMPs, and to determine whether clinical isolates obtained from various patient populations show differences in their susceptibilities to specific AMPs. In addition, we assessed whether changes in AMP susceptibility occur as a result of in-host adaptation.…”

Cathelicidins Modulate TLR-Activation and Inflammation

“…paratuberculosis (MAP), a bacterium causing chronic diarrheic intestinal infections in domestic and wild ruminants, by increasing bacterial uptake in murine macrophages. In addition, macrophage treatment with LL-37 suppresses TLR2 upregulation and thereby the production of tissue-damaging inflammatory cytokines released during MAP infection (153), as well as during A. fumigatus infection (154).…”

The Daisho Peptides Mediate Drosophila Defense Against a Subset of Filamentous Fungi

“…The immunostaining protocol was adapted from Luo et al (29). F. oxysporum was grown in 5 ml malt extract broth from a starting concentration of 2.9 × 10 5 spores/ml.…”

“…In addition, our immunofluorescence data demonstrate that Daisho2 can interact in vitro with at least one filamentous fungus that it targets. Antifungal peptides, such as mammalian LL-37 and plant defensin NaD1, also bind hyphae of fungal pathogens against which they are active (29,37). The Daisho2 peptide's ability to bind fungal hyphae could indicate an antimicrobial function.…”