Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases, Frederick, Maryland, USA.
Antimicrob Agents Chemother. 2011 Sep;55(9):4238-50. doi: 10.1128/AAC.00267-11. Epub 2011 Jul 18.
Retrocyclins are humanized versions of the -defensin peptides expressed by the leukocytes of several nonhuman primates. Previous studies, performed in serum-free media, determined that retrocyclins 1 (RC1) and RC2 could prevent successful germination of Bacillus anthracis spores, kill vegetative B. anthracis cells, and inactivate anthrax lethal factor. We now report that retrocyclins are extensively bound by components of native mouse, human, and fetal calf sera, that heat-inactivated sera show greatly enhanced retrocyclin binding, and that native and (especially) heat-inactivated sera greatly reduce the direct activities of retrocyclins against spores and vegetative cells of B. anthracis. Nevertheless, we also found that retrocyclins protected mice challenged in vivo by subcutaneous, intraperitoneal, or intranasal instillation of B. anthracis spores. Retrocyclin 1 bound extensively to B. anthracis spores and enhanced their phagocytosis and killing by murine RAW264.7 cells. Based on the assumption that spore-bound RC1 enters phagosomes by "piggyback phagocytosis," model calculations showed that the intraphagosomal concentration of RC1 would greatly exceed its extracellular concentration. Murine alveolar macrophages took up fluorescently labeled retrocyclin, suggesting that macrophages may also acquire extracellular RC1 directly. Overall, these data demonstrate that retrocyclins are effective in vivo against experimental murine anthrax infections and suggest that enhanced macrophage function contributes to this property.
Retrocyclins 是几种非人类灵长类白细胞表达的 -defensin 肽的人源化版本。以前的研究在无血清培养基中进行，结果表明 retrocyclins 1 (RC1) 和 RC2 可以阻止炭疽杆菌孢子成功发芽，杀死有活力的炭疽杆菌细胞，并使炭疽致死因子失活。我们现在报告说， retrocyclins 被天然小鼠、人血清和胎牛血清的成分广泛结合，热灭活的血清显示出大大增强的 retrocyclin 结合能力，天然和（特别是）热灭活的血清大大降低了 retrocyclin 对炭疽杆菌孢子和有活力的细胞的直接活性。然而，我们还发现 retrocyclins 可以保护体内接受炭疽杆菌孢子皮下、腹腔内或鼻内滴注挑战的小鼠。 Retrocyclin 1 与炭疽杆菌孢子广泛结合，并增强了它们被小鼠 RAW264.7 细胞吞噬和杀死的能力。基于“搭便车吞噬”假设，即孢子结合的 RC1 通过“搭便车吞噬”进入吞噬体，模型计算表明，吞噬体内的 RC1 浓度将大大超过其细胞外浓度。鼠肺泡巨噬细胞摄取荧光标记的 retrocyclin，表明巨噬细胞也可以直接获得细胞外的 RC1。总的来说，这些数据表明 retrocyclins 对实验性小鼠炭疽感染具有体内有效性，并表明增强的巨噬细胞功能有助于这一特性。
