Structure-function relationship of the human antimicrobial peptide LL-37 and LL-37 fragments in the modulation of TLR responses

Abstract

Cathelicidins are effector molecules of the innate host defense system that establish an antimicrobial barrier at epithelial interfaces. The human cathelicidin LL-37, in addition to its antimicrobial activity, also exhibits immunomodulatory effects, such as inhibition of pro-inflammatory responses to bacterial LPS in human monocytic cells. In this report, we demonstrate that LL-37 almost completely prevents the pro-inflammatory cytokine release by human peripheral blood mononuclear cells (PBMCs) following stimulation with Toll-like receptor (TLR)4 and TLR2/1 agonists while leaving TLR2/6, TLR5, TLR7 and TLR8 responses unchanged. Modulation of the TLR response by LL-37 occurred at least partly through the MAP kinase pathway via inhibition of p38 phosphorylation. By using an LL-37 library with overlapping sequences, we identified the mid-region of LL-37, comprising amino acids 13-31, as the active domain for the modulation of TLR responses. The mechanism of immunomodulation of LL-37 and LL-37 fragments is lipopoly-saccharide binding. Correlations between the capacity of LL-37 fragments to modulate TLR responses and their physico-chemical properties revealed that cationicity and hydrophobicity are essential for the modulation of LL-37-mediated TLR responses.

Chicken cathelicidin-2-derived peptides with enhanced immunomodulatory and antibacterial activities against biological warfare agents

“…In line with our observations, Nan et al [12] showed that substitution of Trp by Lys residues in the Trp-rich peptide indolicidin resulted in decreased hydrophobicity and loss of LPS-neutralising activity. Previously it was shown that inhibition of the pro-inflammatory response is mainly established by direct binding of cationic HDPs to LPS [11,13]. In line with these observations, we found a correlation between LPS-neutralising activities and LPS binding.…”

“…PheTrp substitutions in C1-15, resulting in peptide F2,5,12W, significantly increased the LPS-neutralising capacity. Recently, we [11] and others [12] reported the importance of hydrophobicity in neutralising LPS cytokine responses. In line with our observations, Nan et al [12] showed that substitution of Trp by Lys residues in the Trp-rich peptide indolicidin resulted in decreased hydrophobicity and loss of LPS-neutralising activity.…”

LL-37 Directs Macrophage Differentiation toward Macrophages with a Proinflammatory Signature

“…Preliminary experiments revealed that these C-terminal peptides are more effective than LL-37 in killing of Staphylococcus aureus as detected by radial diffusion assays (T. Vos, A. van der Does, B. Ravensbergen, H. Beekhuizen, and P. Nibbering, unpublished results). In agreement, is has been reported that the LL-37-derived peptides covering residues 13-35 are at least as effective as LL-37 with respect to LPS neutralization (31), modulation of TLR-mediated responses (34), and inducing secondary necrosis of apoptotic neutrophils (35). These structure-function studies can be helpful in the design of new candidate peptides for the treatment of infections.…”

Human Lung Mast Cells Mediate Pneumococcal Cell Death in Response to Activation by Pneumolysin

“…Mouse mast cells deficient in CRAMP, another member of the cathelicidin family, are less able to kill group A Streptococcus (12). In addition, LL-37 can modulate TLR (54) and immune responses. In a recent study, von Köckritz-Blickwede et al (11) demonstrated that the human mast cell line HMC-1 elicited antimicrobial activity that was independent of phagocytosis.…”