Microbes, Immunity, and Behavior: Psychoneuroimmunology Meets the Microbiome

Abstract

There is now a large volume of evidence to support the view that the immune system is a key communication pathway between the gut and brain, which plays an important role in stress-related psychopathologies and thus provides a potentially fruitful target for psychotropic intervention. The gut microbiota is a complex ecosystem with a diverse range of organisms and a sophisticated genomic structure. Bacteria within the gut are estimated to weigh in excess of 1 kg in the adult human and the microbes within not only produce antimicrobial peptides, short chain fatty acids, and vitamins, but also most of the common neurotransmitters found in the human brain. That the microbial content of the gut plays a key role in immune development is now beyond doubt. Early disruption of the host-microbe interplay can have lifelong consequences, not just in terms of intestinal function but in distal organs including the brain. It is clear that the immune system and nervous system are in continuous communication in order to maintain a state of homeostasis. Significant gaps in knowledge remain about the effect of the gut microbiota in coordinating the immune-nervous systems dialogue. However, studies using germ-free animals, infective models, prebiotics, probiotics, and antibiotics have increased our understanding of the interplay. Early life stress can have a lifelong impact on the microbial content of the intestine and permanently alter immune functioning. That early life stress can also impact adult psychopathology has long been appreciated in psychiatry. The challenge now is to fully decipher the molecular mechanisms that link the gut microbiota, immune, and central nervous systems in a network of communication that impacts behavior patterns and psychopathology, to eventually translate these findings to the human situation both in health and disease. Even at this juncture, there is evidence to pinpoint key sites of communication where gut microbial interventions either with drugs or diet or perhaps fecal microbiota transplantation may positively impact mental health.

No regrets: Young adult patients in psychiatry report positive reactions to biobank participation

“…Biological markers are, however, absent and an important dimension of diagnostics and basis for understanding disease etiology is missing. Recent research suggest, for example, that interconnected links between the immune system, the microbiome and the brain are essential for normal brain functions, such as initiating and regulating stress responses, emotions and behavior [1, 2]. The next step is to define clinical markers based on integrated data that reflect biological pathways and look for meaningful clinical differences in large representative patient cohorts.…”

Effect of acute ozone exposure on the lung metabolomes of obese and lean mice

“…However, it is increasingly appreciated that other bacterially derived metabolites contribute to pathological processes not only within the gut but also within the heart, the immune system, and the nervous system [18,74,75]. Indeed, the microbiome has already been shown to play a role in pulmonary responses to allergen [76].…”

Protocol for the Emory University African American Vaginal, Oral, and Gut Microbiome in Pregnancy Cohort Study

“…This possibility is especially compelling given that microbiome functions associate with one or more of the known risk factors for adverse pregnancy outcomes including programming and maintenance of the immune system and protection against infection, [8, 9] the physical and emotional response to acute and chronic stress, [10] harvesting of micronutrients and the digestion and metabolism of food, [11] and the breakdown and absorption of toxins [12]. …”