Evolution of both host resistance and tolerance to an emerging bacterial pathogen
Evolution of both host resistance and tolerance to an emerging bacterial pathogen
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DOI：
10.1002/evl3.133
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发表时间：
2019-08-14
影响因子：
5
通讯作者：
Wilson, Alastair J.
中科院分区：
文献类型：
--
作者：
Bonneaud, Camille;Tardy, Luc;Wilson, Alastair J.
了解宿主如何最大限度地减少新出现感染的成本对于流行病学动态和病原体毒力的演变具有根本性影响。尽管如此，很少有针对自然群体的实验研究测试了宿主是否会为了应对疾病的出现而进化出抵抗力（通过免疫激活来减少病原体负荷）或耐受性（在不减少病原体负荷的情况下限制体细胞损伤）。此外，尽管已知对宿主对感染的反应有影响，但没有人这样做来解释病原体毒力的显着自然变化。在这里，我们调查北美东部家雀（Haemorhous mexicanus）是否已经进化出对其新出现的细菌病原体鸡毒支原体的抵抗力和/或耐受性。为此，我们给暴露于疾病和未暴露于疾病的雀类群体中接种了 55 种具有不同毒力的不同菌株。首先，虽然在接种后大约八天发生的峰值病原体负荷在来自疾病暴露群体的实验接种的雀类与未暴露群体的雀类之间没有差异，但病原体负荷随后在来自暴露群体的雀类中下降得更快并且程度更大。这些结果表明，来自暴露种群的雀类能够通过适应性免疫过程清除感染。然而，其次，对于给定的病原体负荷，来自暴露种群的雀类也表现出较低的症状严重程度，这表明损害限制机制或耐受性伴随着免疫清除的进化。我们的研究结果强调，耐药性和耐受性应被视为互补而非替代的防御策略：耐药性的进化受益于耐受机制的同时进化，该机制可防止免疫激活的损害，而没有耐药性的耐受性进化将面临病原体毒力选择失控的风险。
Understanding how hosts minimize the cost of emerging infections has fundamental implications for epidemiological dynamics and the evolution of pathogen virulence. Despite this, few experimental studies in natural populations have tested whether, in response to disease emergence, hosts evolve resistance, which reduces pathogen load through immune activation, or tolerance, which limits somatic damages without decreasing pathogen load. Further, none has done so accounting for significant natural variation in pathogen virulence, despite known effects on host responses to infection. Here, we investigate whether eastern North American house finches (Haemorhous mexicanus) have evolved resistance and/or tolerance to their emerging bacterial pathogen, Mycoplasma gallisepticum. To do so, we inoculated finches from disease-exposed and disease-unexposed populations with 55 distinct isolates of varying virulence. First, although peak pathogen loads, which occurred approximately eight days postinoculation, did not differ between experimentally inoculated finches from disease-exposed versus unexposed population, pathogen loads subsequently decreased faster and to a greater extent in finches from exposed populations. These results suggest that finches from exposed populations are able to clear the infection through adaptive immune processes. Second, however, finches from exposed populations also displayed lower symptom severity for a given pathogen load, suggesting that a damage-limitation mechanism, or tolerance, has accompanied the evolution of immune clearance. Our results highlight that resistance and tolerance should be seen as complementary, not alternative, defense strategies: the evolution of resistance benefits from the concomitant evolution of tolerance mechanisms that protect against the damage of immune activation, whereas the evolution of tolerance without resistance will risk runaway selection on pathogen virulence.