Departments of Microbiology and Immunology and of Pediatrics, Vanderbilt University Medical Center, Nashville, Tennessee 37232.
Integr Comp Biol. 2005 Jan;45(1):137-42. doi: 10.1093/icb/45.1.137.
One of the most urgent problems in conservation biology today is the continuing loss of amphibian populations on a global scale. Recent amphibian population declines in Australia, Central America, the western United States, Europe, and Africa have been linked to a pathogenic chytrid fungus, Batrachochytrium dendrobatidis, which infects the skin. The skin of amphibians is critical for fluid balance, respiration, and transport of essential ions; and the immune defense of the skin must be integrated with these physiological responses. One of the natural defenses of the skin is production of antimicrobial peptides in granular glands. Discharge of the granular glands is initiated by stimulation of sympathetic nerves. To determine whether antimicrobial skin peptides play a role in protection from invasive pathogens, purified antimicrobial peptides and natural peptide mixtures recovered from the skin secretions of a number of species have been assayed for growth inhibition of the chytrid fungus. The general findings are that most species tested have one or more antimicrobial peptides with potent activity against the chytrid fungus, and natural mixtures of peptides are also effective inhibitors of chytrid growth. This supports the hypothesis that antimicrobial peptides produced in the skin are an important defense against skin pathogens and may affect survival of populations. We also report on initial studies of peptide depletion using norepinephrine and the kinetics of peptide recovery following induction. Approximately 80 nmoles/g of norepinephrine is required to deplete peptides, and peptide stores are not fully recovered at three weeks following this treatment. Because many species have defensive peptides and yet suffer chytrid-associated population declines, it is likely that other factors (temperature, conditions of hydration, "stress," or pesticides) may alter normal defenses and allow for uncontrolled infection.
目前保护生物学领域最紧迫的问题之一是，全球范围内的两栖动物种群仍在持续减少。最近，澳大利亚、中美洲、美国西部、欧洲和非洲的两栖动物种群数量下降与一种致病性的壶菌真菌有关，即棘口吸虫（Batrachochytrium dendrobatidis），它感染皮肤。两栖动物的皮肤对于体液平衡、呼吸和必需离子的运输至关重要；皮肤的免疫防御必须与这些生理反应相整合。皮肤的天然防御之一是在颗粒腺中产生抗菌肽。颗粒腺的分泌是由交感神经的刺激引发的。为了确定抗菌皮肤肽是否在抵御入侵病原体方面发挥作用，从多种物种的皮肤分泌物中提取的纯化抗菌肽和天然肽混合物已被用于检测对棘口吸虫的生长抑制作用。总的研究结果表明，大多数测试的物种都有一种或多种对棘口吸虫具有强大活性的抗菌肽，而且天然肽混合物也是棘口吸虫生长的有效抑制剂。这支持了这样一种假设，即皮肤中产生的抗菌肽是抵御皮肤病原体的重要防御机制，可能会影响种群的生存。我们还报告了使用去甲肾上腺素进行肽耗竭的初步研究以及诱导后肽恢复的动力学。大约需要 80nmoles/g 的去甲肾上腺素来耗尽肽，并且在经过这种处理后的三周内，肽库没有完全恢复。由于许多物种都有防御性肽，但仍遭受棘口吸虫相关的种群减少，因此其他因素（温度、水合条件、“压力”或杀虫剂）可能会改变正常的防御机制，从而导致不受控制的感染。
