Data_Sheet_1_Host Resistance to Bacterial Infection Varies Over Time, but Is Not Affected by a Previous Exposure to the Same Pathogen.docx

Immune priming describes the phenomenon whereby after a primary pathogen exposure, a host more effectively fights a lethal secondary exposure (challenge) to the same pathogen. Conflicting evidence exists for immune priming in invertebrates, potentially due to heterogeneity across studies in the pathogen species tested, the antigen preparation for the primary exposure, and the phenotypic trait used to test for priming. To explore these factors, we injected Drosophila melanogaster with one of two bacterial species, Lactococcus lactis or Providencia burhodogranariea, which had either been heat-killed or inactivated with formaldehyde, or we injected a 1:1 mixture of the two inactivation methods. Survival and resistance (the inverse of bacterial load) were assessed after a live bacterial challenge. In contrast to our predictions, none of the primary exposure treatments provided a survival benefit after challenge compared to the controls. Resistance in the acute phase, i.e., 1 day post-challenge, separated into a lower- and higher-load group, however, neither group varied according to the primary exposure. In the chronic phase, i.e., 7 days post-challenge, resistance did not separate into two groups, and it was also unaffected by the primary exposure. Our multi-angled study supports the view that immune priming may require specific circumstances to occur, rather than it being a ubiquitous aspect of insect immunity.

免疫原性激活描述了一种现象，即宿主在首次暴露于原发病原体之后，能够更有效地抵御同一种病原体的致命性二次暴露（挑战）。关于无脊椎动物免疫原性激活的证据存在冲突，这或许是由于不同研究中测试的病原体物种的异质性、首次暴露所用的抗原制备以及用于检测原性激活的表型特征所导致的。为了探讨这些因素，我们向黑腹果蝇注射了两种细菌物种之一，即乳酸链球菌或普罗维登西亚杆菌，这些细菌要么经过热灭活，要么用甲醛进行灭活，或者注射两种灭活方法的1:1混合物。在活细菌挑战之后，评估了存活率和抵抗力（细菌载量的倒数）。与我们的预测相反，与对照相比，所有首次暴露处理在挑战后并未提供生存上的益处。在急性阶段，即挑战后1天，抵抗力分为低载量和高载量两组，然而，两组均未根据首次暴露而有所变化。在慢性阶段，即挑战后7天，抵抗力并未分为两组，并且也未受到首次暴露的影响。我们的多角度研究支持了这样一个观点：免疫原性激活可能需要特定的条件才能发生，而不是昆虫免疫的普遍特性。