Supplementary Material for: Activity, Expression and Genetic Variation of Canine β-Defensin 103: A Multifunctional Antimicrobial Peptide in the Skin of Domestic Dogs

The skin functions as more than a physical barrier to infection. Epithelial cells of the skin can synthesize antimicrobial peptides, including defensins, which exhibit direct antimicrobial activity. Here we characterize the expression pattern, genetic variation and activity of the major β-defensin expressed in canine skin, canine β-defensin 103 (CBD103). The gene encoding CBD103 exhibits two forms of polymorphism: a common 3-basepair deletion allele and a gene copy-number variation. Golden retrievers and Labrador retrievers were the only breeds that encoded the variant allele of CBD103, termed CBD103ΔG23. Both these breeds also exhibited a CBD103 gene copy-number polymorphism that ranged from 2 to 4 gene-copies per diploid genome. Recombinant CBD103 and CBD103ΔG23, as well as the human ortholog human β-defensin 3 (hBD3) and hBD3ΔG23, showed potent and comparable antimicrobial killing against both methicillin-susceptible and methicillin-resistant Staphylococcus pseudintermedius. Skin biopsy specimens from dogs with atopic dermatitis revealed CBD103 expression levels similar to those in healthy controls and comparable at lesional and nonlesional sites. This expression pattern in dogs differs from the previously reported reduced expression of the human ortholog in atopic dermatitis. Overall, the similarities of CBD103 and its human ortholog reported here support the notion that the domestic dog may serve as a valuable model for studying β-defensin biology in the skin.

皮肤并非仅作为抵御感染的物理屏障。皮肤上皮细胞可合成包括防御素在内的抗菌肽，这类物质具备直接抗菌活性。
本研究对犬皮肤主要表达的β-防御素（β-defensin）——犬β-防御素103（canine β-defensin 103, CBD103）的表达模式、遗传变异与抗菌活性进行了系统表征。
编码CBD103的基因存在两种多态性形式：一种为常见的3碱基缺失等位基因，另一种为基因拷贝数变异。金毛寻回犬与拉布拉多寻回犬是仅有的两种携带CBD103变异等位基因（命名为CBD103ΔG23）的犬种，这两个品种同时也存在CBD103基因拷贝数多态性，其二倍体基因组中的基因拷贝数范围为2至4份。
重组CBD103、CBD103ΔG23，以及其人类直系同源蛋白人类β-防御素3（human β-defensin 3, hBD3）和hBD3ΔG23，均对甲氧西林敏感型和甲氧西林耐药型中间葡萄球菌（Staphylococcus pseudintermedius）展现出强效且活性相当的抗菌杀伤效果。
特应性皮炎患犬的皮肤活检样本显示，其CBD103表达水平与健康对照组相近，且皮损部位与非皮损部位的表达水平无显著差异。
这种犬类的表达模式与此前报道的人类同源基因在特应性皮炎中表达下调的情况存在显著差异。
总体而言，本研究揭示的CBD103与其人类直系同源蛋白的相似性，支持家犬可作为研究皮肤β-防御素生物学特性的优质动物模型这一观点。