Department of Molecular Biology and Functional Genomics, University of Stockholm, Stockholm, Sweden.
J Innate Immun. 2009;1(4):301-8. doi: 10.1159/000168009. Epub 2008 Oct 30.
The enzyme phenoloxidase (PO) is one of the first immune molecules that was identified in invertebrates. Recently, the immune function of PO has been challenged. We tested how PO is activated following injury in 2 insects, i.e. the fruit fly Drosophila melanogaster and the wax moth Galleria mellonella. Rapid PO activation in Drosophila was limited to discrete areas of the hemolymph clot which forms after injury. Surprisingly, unlike systemic PO activation during bacterial sepsis, clot melanization was not sensitive to microbial elicitors in our assay. Instead, Drosophila clot melanization was activated by endogenous signals such as apoptotic cells and was superinduced by phosphatidylserine, a negatively charged phospholipid normally found on the inner surface of the plasma membrane and exposed during apoptosis. In contrast, melanization in G. mellonella hemolymph was stronger and more uniform and was sensitive to peptidoglycan. This shows that both exogenous and endogenous signals can trigger the same immune mechanism in species- and context-dependent ways. Our findings have implications for the evolutionary dynamics of immune mechanisms and are in agreement with recent comparisons of insect immune transcriptomes.
酚氧化酶（PO）是最早在无脊椎动物中鉴定出的免疫分子之一。最近，PO 的免疫功能受到了挑战。我们测试了 2 种昆虫（果蝇 Drosophila melanogaster 和蜡蛾 Galleria mellonella）受伤后 PO 是如何被激活的。果蝇中 PO 的快速激活仅限于受伤后形成的血液凝块的离散区域。令人惊讶的是，与细菌败血症期间的全身性 PO 激活不同，在我们的实验中，凝块黑化对微生物诱导剂不敏感。相反，果蝇凝块黑化是由内源性信号（如凋亡细胞）激活的，并且被带负电荷的磷脂酰丝氨酸超诱导，该磷脂通常存在于质膜的内表面，在凋亡过程中暴露。相比之下，蜡蛾血液中的黑化更强且更均匀，并且对肽聚糖敏感。这表明，外源性和内源性信号都可以以物种和环境依赖的方式触发相同的免疫机制。我们的发现对免疫机制的进化动态具有启示意义，并与最近对昆虫免疫转录组的比较结果一致。
