Understanding biological mechanisms underlying absorption of immunoglobulins in newborn ruminants

在犊牛中，断奶前发病率和死亡率仍然很高，分别为24%和6%。发病率和死亡率风险的一个强有力的预测因素是未能吸收初乳中的免疫球蛋白。在出生时，牛犊没有免疫球蛋白，而免疫球蛋白是抵御疾病所需的；在它们产生自己的免疫球蛋白之前，牛犊的整个适应性免疫反应依赖于吸收初乳中喂养的免疫球蛋白的能力。由于新生犊牛免疫球蛋白吸收时间窗口较短，免疫球蛋白吸收效率较低，为25%-50%。经典研究表明，免疫球蛋白的吸收在生命的前六个小时会迅速减少。喂养初乳和初乳中的高细菌含量都会进一步减少免疫球蛋白的吸收，直到生命24小时停止免疫球蛋白吸收。免疫球蛋白吸收停止被称为“肠道闭合”，直到最近还被认为在生命24小时相对不变。我们团队最近的一项研究表明，免疫球蛋白吸收窗口实际上可以通过补充初乳中的丁酸盐来操纵。尽管丁酸盐对免疫球蛋白吸收有负面影响，但仅仅是免疫球蛋白吸收窗口可以被营养地操纵这一事实本身就具有提高免疫球蛋白吸收效率的巨大潜力。这项拟议的研究的目的是提高我们对免疫球蛋白吸收在新生牛犊中的调节方式的理解。我的假设是，免疫球蛋白的吸收主要依赖于FcRN，并受细胞增殖和上皮屏障完整性的调节。为了验证这一假设，拟议的研究有几个具体的目标：1)确定上皮成熟对免疫球蛋白运输的作用；2)调查FcRN依赖的和细胞旁运输在免疫球蛋白吸收中的作用；以及3)调查管腔细菌负荷对免疫反应和紧密连接形成的影响。为了验证这一假设并达到特定的目标，将进行一系列实验，包括体内和体外方法，并使用从运输动力学到显微镜再到转录组学的各种分析技术，以整体方法提高我们对幼犊免疫球蛋白吸收的理解。拟议的工作将支持一名博士、两名硕士和两名本科生。总之，拟议的研究将提高我们对免疫球蛋白在幼犊体内运输调节的理解，从而加强我们对影响大分子吸收生理的生物系统的理解。

In calves, pre-weaning morbidity and mortality remain high, at 24% and 6%, respectively. A strong predictive factor of morbidity and mortality risk is a failure to absorb immunoglobulins in colostrum. At birth, calves have no immunoglobulins, which are needed to fight off disease; until they produce their own immunoglobulins, the calf's entire adaptive immune response rests on the ability to absorb immunoglobulins fed in colostrum. Efficiency of immunoglobulin absorption is low, ranging from 25 - 50%, owing to the short time window for immunoglobulin absorption in neonatal calves. Classical research demonstrated immunoglobulin absorption to decrease rapidly in the first six hours of life. Both feeding of colostrum as well as a high bacterial load in colostrum further decrease immunoglobulin absorption, until cessation of immunoglobulin absorption at 24h of life. The cessation of immunoglobulin absorption is known as "gut closure" and was, until recently, thought to be relatively immutable at 24h of life. Recent research from our team indicates that the immunoglobulin absorption window can actually be manipulated by supplementing colostrum with butyrate. Despite the negative impact of butyrate on immunoglobulin absorption, the mere fact that the immunoglobulin absorption window can be nutritionally manipulated holds great potential to improve efficacy of immunoglobulin absorption. The objective of the proposed research is to improve our understanding of how immunoglobulin absorption is regulated in newborn calves. My hypothesis is that immunoglobulin absorption is predominantly FcRn-dependent and is regulated by cellular proliferation and establishment of epithelial barrier integrity. To test this hypothesis, the proposed research has several specific objectives: 1) Determine the role of epithelial maturation on immunoglobulin transport; 2) Investigate the role of FcRn-dependent and paracellular transport in immunoglobulin absorption; and 3)Investigate the impact of luminal bacterial load on immune response and tight junction formation. To test this hypothesis and meet the specific objectives, a series of experiments will be conducted that include in vivo and in vitro methods, and use a variety of analytical techniques from transport kinetics to microscopy to transcriptomics for a holistic approach to improving our understanding of immunoglobulin absorption in young calves. The proposed work will support one PhD, two MSc, and two undergraduate students. In all, the proposed research will improve our understanding of the regulation of immunoglobulin transport in young calves, thereby bolstering our understanding of the biological systems influencing absorption physiology of macromolecules.