The role of the gut microbiome in shaping the immune system of chickens.

Most animals are colonised by at least as many microbial cells as somatic cells, potentially comprising at least 100 times more genes within just the gut microbiota than the host itself. It is, therefore, evident that such a conglomeration can have a profound effect on various bodily systems, particularly the (gut) immune system. Chickens are major providers of efficiently produced protein for humans but also harbour common foodborne pathogens and are susceptible to significant and costly diseases, making a thorough understanding of the influence of the gut microbiome on the immune system very pertinent. Major colonisation of the chicken intestine occurs after hatch and this, along with subsequent microbiota composition and activity, are influenced by numerous host and environmental factors, such that each individual has a unique microbiome signature. However, both extreme (e.g. germ free) and more subtle (e.g. diet changes) microbiome modifications can profoundly impact the development of the gut immune system, particularly adaptive immune apparatus and function. This review will consider the influence of the chicken gut microbiome on immune system development, the implications of this relationship in terms of disease susceptibility, vaccine response, optimal health and productivity, and thus exogenous approaches to positively shape microbiome-immune system interactions.