Abstract
Infectious diseases and infections remain a leading cause of death in low-income countries and a major risk to vulnerable groups, such as infants and the elderly. The immune system plays a crucial role in the susceptibility, persistence, and clearance of these infections. With 70–80% of immune cells being present in the gut, there is an intricate interplay between the intestinal microbiota, the intestinal epithelial layer, and the local mucosal immune system. In addition to the local mucosal immune responses in the gut, it is increasingly recognized that the gut microbiome also affects systemic immunity. Clinicians are more and more using the increased knowledge about these complex interactions between the immune system, the gut microbiome, and human pathogens. The now well-recognized impact of nutrition on the composition of the gut microbiota and the immune system elucidates the role nutrition can play in improving health. This review describes the mechanisms involved in maintaining the intricate balance between the microbiota, gut health, the local immune response, and systemic immunity, linking this to infectious diseases throughout life, and highlights the impact of nutrition in infectious disease prevention and treatment.
Highlights
anti-microbial peptides (AMPs) are essential components of the innate immune defense and work to limit pathogen interaction with the epithelium. Their expression can be down-regulated by certain pathogens and enhanced by the presence of specific microorganisms and, the composition of the microbiota is key in shaping the innate immune response [4,8]
Another mechanism through which the microbiota steers the immune response is through the formation of metabolites produced by the gut microbiome from dietary components, host products, or other microbial metabolites [28]
It is increasingly recognized that the gut microbiome, besides regulating the local mucosal immune system, affects innate and adaptive cell-mediated systemic immune responses through a variety of mechanisms [37]
Summary
In the Western world, the incidence of infectious diseases has reduced significantly during the past decades owing to improved hygiene, vaccination, and the use of antibiotics [1]. Nearly one-third of deaths are still associated with infectious diseases. Infections still pose a significant risk for vulnerable people, such as infants and the elderly. Upper respiratory tract infections are the most common disease for which individuals seek medical care and, in elderly people, both influenza and pneumonia are still a common cause of death [1]. The World Health Organization states that infectious enteric disease is one of the main causes of death and, according to the Global Burden of Diseases, Injuries, and Risk Factors Study of 2015, infectious diarrhea is a major cause of death worldwide, with a large percentage of these deaths occurring in the under 5 age group [2,3]
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