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Cathelicidin host defense peptides (cHDPs) widely exist in animals with the functions of innate immunity and acquired immunity. To investigate the tissue and sequential expression patterns of the dCATH gene, which encodes the only cHDPs found in waterfowls, we analyzed the internal organs of healthy ducks (Shaxoxing Sheldrake) from 1-day-old to 28-day-old raised in the natural environment. The dCATH mRNA expression level across tissues was determined via quantitative real-time polymerase chain reaction (qRT-PCR). Monoclonal antibody against the mature dCATH peptide used in enzyme-linked immunosorbent assay (ELISA) was prepared by the lymphocyte hybridoma technique for the first time. The concentration of the dCATH peptide in tissues was determined by ELISA. It showed that the dCATH mRNA had a clear tissue-specificity and age-dependent expression pattern, and it was highly expressed in the bone marrow and moderately expressed in the liver, kidney, spleen, pancreas and bursa of healthy duck. The peptide levels of dCATH in liver, kidney, spleen, pancreas and bursa changed with the age of duck, and the peptide concentration in these organs was between 88 and 128 ng/g tissue. For the first time, we characterized the concentration of the cHDP dCATH in vivo. Our study may represent new insights into the crosstalk of innate immunity, tissue development and age. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) have attracted more attention for their potential candidates for new antibiotic drugs. As a novel identified cathelicidin AMP from duck, dCATH owns broad-spectrum antimicrobial activities but with a noticeable toxicity. To explore dCATH-derived AMPs with reduced cell toxicity and improved cell selectivity, a series of truncated and tryptophan-replaced peptides of dCATH were designed. Two truncated peptides containing one of the two tryptophan (Trp) residues at the positions of 4 and 17 (W4 and W17) of dCATH, dCATH(1–16) and dCATH(5–20), showed strong antibacterial activity, but didn't show obvious hemolytic activity and cytotoxicity. The derived peptides not containing Trp didn't possess obvious antimicrobial activity, and their hemolytic and cytotoxic effect was also diminished. Also as evidence by Trp fluorescence experiment that existence of W4 and W17 was crucially important to the antimicrobial activity, hemolysis and cytotoxicity of dCATH, and one of the two Trp residues was competent and necessary to retain its antimicrobial activity. Antibacterial mechanism analysis showed that dCATH(1–16) and dCATH(5–20) killed bacterial cells by increasing permeability and causing a loss of membrane integrity. dCATH(1–16) and dCATH(5–20) possessed insignificant inhibitory activity against levels of IL-6, TNF-α, and NO in RAW 264.7 cells treated with LPS. In vivo , intraperitoneal administration of the two peptides significantly decreased mortality and provided protection against LPS-induced inflammation in mice challenged with lethal dose of LPS. The two peptides, dCATH(1–16) and dCATH(5–20), which possessed high antibacterial activity and cell selectivity, may herald development prospects as new antibacterial agents in the future. [ABSTRACT FROM AUTHOR]