Two arms are better than one: parasite variation leads to combined inducible and constitutive innate immune responses
Two arms are better than one: parasite variation leads to combined inducible and constitutive innate immune responses
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DOI：
10.1098/rspb.2007.1574
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发表时间：
2008-04-22
影响因子：
4.7
通讯作者：
Boots, Mike
中科院分区：
文献类型：
--
作者：
Hamilton, Ruth;Siva-Jothy, Mike;Boots, Mike
寄生虫是所有生物的主要威胁，导致了一系列复杂而有效的防御机制的进化。脊椎动物和无脊椎动物共同的是先天免疫机制，其可以组成型表达或在暴露于感染时诱导。在自然界中，我们发现脊椎动物、无脊椎动物和植物在接触寄生虫时，会采用诱导和组成性反应的组合。在这里，我们使用一个简单的内宿主模型的动机昆虫免疫系统，组成和诱导的反应，以解决为什么这两种类型的反应保持如此普遍的问题。一般来说，诱导反应被认为是有利的，因为它们只在需要时使用，但成本太高，无法持续维持，而组成性反应是有利的，因为它们总是准备好采取行动。然而，使用一个简单的成本函数，但没有先验假设的相对成本，我们表明，寄生虫生长率的变化选择的策略，结合了组成和诱导防御。因此，采用这两种形式的抗辩，并不需要以不同的费用作为理由。显然，宿主很可能受到自然界中各种寄生虫的挑战，这足以解释为什么最好部署先天免疫系统的双臂。
Parasites represent a major threat to all organisms which has led to the evolution of an array of complex and effective defence mechanisms. Common to both vertebrates and invertebrates are innate immune mechanisms that can be either constitutively expressed or induced on exposure to infection. In nature, we find that a combination of both induced and constitutive responses are employed by vertebrates, invertebrates and, to an extent, plants when they are exposed to a parasite. Here we use a simple within-host model motivated by the insect immune system, consisting of both constitutive and induced responses, to address the question of why both types of response are maintained so ubiquitously. Generally, induced responses are thought to be advantageous because they are only used when required but are too costly to maintain constantly, while constitutive responses are advantageous because they are always ready to act. However, using a simple cost function but with no a priori assumptions about relative costs, we show that variability in parasite growth rates selects for a strategy that combines both constitutive and induced defences. Differential costs are therefore not necessary to explain the adoption of both forms of defence. Clearly, hosts are likely to be challenged by variable parasites in nature and this is sufficient to explain why it is optimal to deploy both arms of the innate immune system.