Department of Animal Sciences, University of Florida, Florida, USA.
Department of Animal and Veterinary Science, University of Idaho, Idaho, USA.
Sci Rep. 2020 Jun 16;10(1):9712. doi: 10.1038/s41598-020-66326-w.
Dairy calves are born with a naïve immune system, making the pre-weaning phase a critical window for immune development. In the U.S., 40-60% of dairy farms feed milk replacer to pre-weaned calves, which are devoid of bioactive factors with immunological roles. Serotonin is a bioactive factor with immunoregulatory properties naturally produced by the calf and present in milk. Human and rodent immune cells express the serotonin machinery, but little is known about the role of serotonin in the bovine immune system. Supplementing milk replacer with 5-hydroxytryptophan (serotonin precursor) or fluoxetine (reuptake inhibitor) increases serotonin bioavailability. We hypothesized that increased serotonin bioavailability promotes serotonergic signaling and modulates the expression of immune related genes in peripheral leukocytes and immune-related tissues of dairy calves. The present experiment targeted candidate genes involved in serotonin production, metabolism, transport, signaling and immune regulation. We established that bovine peripheral leukocytes express all known serotonin receptors, and can synthesize, uptake and degrade serotonin due to the expression of serotonin metabolism-related genes. Indeed, we showed that increasing serotonin bioavailability alters gene expression of serotonin receptors and immune-related genes. Further research will determine whether manipulation of the serotonin pathway could be a feasible approach to bolster dairy calves' immune system.
犊牛出生时免疫系统尚未成熟，因此哺乳期是其免疫系统发育的关键时期。在美国，40-60%的奶牛场会给哺乳期前的犊牛喂食代乳粉，而代乳粉中缺乏具有免疫作用的生物活性因子。血清素是一种具有免疫调节特性的生物活性因子，由犊牛自然产生并存在于牛奶中。人类和啮齿动物的免疫细胞表达血清素机制，但关于血清素在牛的免疫系统中的作用知之甚少。通过在代乳粉中添加 5-羟色氨酸（血清素前体）或氟西汀（再摄取抑制剂）可以增加血清素的生物利用度。我们假设增加血清素的生物利用度可以促进血清素能信号传导，并调节奶牛外周白细胞和免疫相关组织中与免疫相关的基因表达。本实验的目的是研究与血清素产生、代谢、转运、信号转导和免疫调节相关的候选基因。我们证实了牛外周白细胞表达所有已知的血清素受体，并且由于表达了与血清素代谢相关的基因，能够合成、摄取和降解血清素。事实上，我们发现增加血清素的生物利用度会改变血清素受体和免疫相关基因的表达。进一步的研究将确定是否可以通过操纵血清素途径来增强奶牛犊牛的免疫系统。
