Data from: Evolution of defence cocktails: antimicrobial peptide combinations reduce mortality and persistent infection

The simultaneous expression of costly immune effectors such as multiple antimicrobial peptides is a hallmark of innate immunity of multicellular organisms, yet the adaptive advantage remains unresolved. Here we test current hypotheses on the evolution of such defence cocktails. We use RNAi gene knock-down to explore, the effects of three highly-expressed antimicrobial peptides, displaying different degrees of activity in vitro against Staphylococcus aureus, during an infection in the beetle Tenebrio molitor. We find that a defensin confers no survival benefit, but reduces bacterial loads. A coleoptericin contributes to host survival without affecting bacterial loads. An attacin has no individual effect. Simultaneous knock-down of the defensin with the other AMPs results in increased mortality and elevated bacterial loads. Contrary to common expectations, the effects on host survival and bacterial load can be independent. The expression of multiple AMPs increases host survival, and contributes to the control of persisting infections and tolerance. This is an emerging property that explains the adaptive benefit of defence cocktails.

共表达多种抗菌肽（antimicrobial peptides）这类耗能的免疫效应分子，是多细胞生物先天免疫的标志性特征，但其适应性优势的演化机制至今尚未阐明。本研究针对这类免疫防御组合的演化假说开展检验。我们借助RNA干扰（RNAi）基因敲低技术，探究黄粉虫（Tenebrio molitor）感染金黄色葡萄球菌（Staphylococcus aureus）时，三种体外对该菌具有不同程度抗菌活性的高表达抗菌肽所发挥的作用。研究结果显示：防御素（defensin）虽可降低细菌载量，但无法为宿主带来存活优势；鞘翅肽（coleoptericin）可提升宿主存活率，但不会改变细菌载量；嗜菌素（attacin）单独发挥作用时无显著效果。同时敲低防御素与其他抗菌肽的表达，会导致宿主死亡率上升与细菌载量升高。与主流预期相悖的是，抗菌肽对宿主存活与细菌载量的调控作用可以相互独立。多种抗菌肽的共表达可提升宿主存活率，有助于控制持续性感染并维持免疫耐受。这一新兴特性阐明了免疫防御组合的适应性优势来源。