Periodic Reporting for period 1 - IMPRINT (Immunological and Microbiota Priming of the Response to Infection)
Berichtszeitraum: 2022-03-21 bis 2024-03-20
The incidence of infectious diseases has declined in the past 100 years due to the widespread use of vaccines and antimicrobials, improved hygiene practices and advances in healthcare approaches. Concurrently, inflammatory disorders such as asthma, type 1 diabetes and inflammatory bowel disease have increased. However, recent global pandemics and steadily growing antimicrobial resistance show that infectious diseases remain a serious threat to human health. Exposure to microorganisms in early life is a critical process that helps to train the human immune system to recognise and respond to invading pathogens later in life. However, emerging evidence indicates that humans harbour a highly diverse community of intestinal microorganisms (gut microbiota), much of which remains uncharacterised. Therefore, microbiota-immune interactions in early life are highly complex and may influence immune responses to both infection and inflammatory disease in adulthood. The gut microbiota is limited in diversity during the first months of life. Upon the introduction of solid foods (weaning), it diversifies rapidly. This programmed diversification of the gut microbiota exposes the immune system to a vast array of microbes, antigens and metabolites. In animal models, this early-life gut microbiota ‘imprints’ tolerance in the immune system to particular inflammatory stimuli, thereby protecting mice against inflammatory disorders such as allergy and colitis. However, the mechanisms of immune imprinting remain largely unknown. Current evidence in humans is only observational. However, this evidence indicates that antibiotics and other exposures that impair the maturation of the early-life gut microbiota, such as C-section birth and formula feeding, are associated with increased risk of later immune-mediated disorders such as asthma, inflammatory bowel disease and type 1 diabetes. Similarly, early-life antibiotic exposure is associated with increased susceptibility to later infections. Therefore, the early-life gut microbiota may influence immune system responses later in life. However, the influence of the early-life gut microbiota on later life immune response to infection is poorly characterised. Understanding how the gut microbiota trains the immune system to respond to later life infection would have major implications on medical approaches to tackle infectious diseases. With ever-present threats of global pandemics and expanding antimicrobial resistance, it is essential to identify new strategies to target infectious diseases. This project has the potential to uncover novel mechanisms by which the early-life gut microbiota trains immune responses to later life infection and therefore may help to uncover novel preventative therapies or therapeutic targets for infectious diseases. The overall objectives of the project were:
1. To evaluate the impact of the gut microbiota on the susceptibility to intestinal infection in adulthood
2. To establish whether microbiota-induced immune cells in the intestine influence susceptibility and immune response to intestinal infection in adulthood
3. To identify specific gut microbes and/or microbial metabolites during weaning that promote induction of intestinal immune cells and modulate subsequent susceptibility to intestinal infection in adulthood
This project found that exposure to antibiotics during early-life reduced early colonization of an intestinal pathogen (Citrobacter rodentium) in male mice during adulthood in addition to a reduced inflammatory response in the intestine. This may be due, in part, to changes induced by the early-life gut microbiota on intestinal epithelial cells. Collectively, the project found a role of the early-life gut microbiota on the immune response to infection in adulthood.
1. To evaluate the impact of the gut microbiota on the susceptibility to intestinal infection in adulthood
2. To establish whether microbiota-induced immune cells in the intestine influence susceptibility and immune response to intestinal infection in adulthood
3. To identify specific gut microbes and/or microbial metabolites during weaning that promote induction of intestinal immune cells and modulate subsequent susceptibility to intestinal infection in adulthood
This project found that exposure to antibiotics during early-life reduced early colonization of an intestinal pathogen (Citrobacter rodentium) in male mice during adulthood in addition to a reduced inflammatory response in the intestine. This may be due, in part, to changes induced by the early-life gut microbiota on intestinal epithelial cells. Collectively, the project found a role of the early-life gut microbiota on the immune response to infection in adulthood.
Months 1-6 of the action included obtaining all ethical approvals, training certifications and experimental licences in order to initiate animal infection experiments. Training courses in A3 animal facility procedures, A3 first aid and health and safety, biological and chemical training, histology training for intestinal imaging and flow cytometry training for immune cell analyses were all completed during this initial period also. Preliminary experiments were also conducted during this period.
During months 7-21 of the action involved conducting of experiments directly related to the proposed work. Three independent sets of experiments were conducted during this 14 month period. Briefly, muring mothers and pups were treated with or without a cocktail of antibiotics from day 5-28 of life after which the offspring were weaned into separate cages. At 8 weeks of life, mice were infected with 10(9) colony-forming units of Citrobacter rodentium, by oral gavage, and fecal samples were collected every second day for up to 14 days to test for pathogen abundance. Following infection, intestinal inflammatory genes, inflammatory cytokines, tissue lymphocyte proportions were all assessed at either day 5 (short term infection) or day 10/14 (long-term infection).
In brief, we found that exposure to early-life antibiotics reduced colonization of C. rodentium in the first 3 days of infection, only in male mice, however pathogen colonization was similar between both antibiotic treated and non-treated mice after 3 days. Inflammatory gene expression was also also reduced in antibiotic exposed mice compared with non-antibiotic treated, infected mice.
During months 7-21 of the action involved conducting of experiments directly related to the proposed work. Three independent sets of experiments were conducted during this 14 month period. Briefly, muring mothers and pups were treated with or without a cocktail of antibiotics from day 5-28 of life after which the offspring were weaned into separate cages. At 8 weeks of life, mice were infected with 10(9) colony-forming units of Citrobacter rodentium, by oral gavage, and fecal samples were collected every second day for up to 14 days to test for pathogen abundance. Following infection, intestinal inflammatory genes, inflammatory cytokines, tissue lymphocyte proportions were all assessed at either day 5 (short term infection) or day 10/14 (long-term infection).
In brief, we found that exposure to early-life antibiotics reduced colonization of C. rodentium in the first 3 days of infection, only in male mice, however pathogen colonization was similar between both antibiotic treated and non-treated mice after 3 days. Inflammatory gene expression was also also reduced in antibiotic exposed mice compared with non-antibiotic treated, infected mice.
This project has progressed knowledge beyond the state-of-the-art regarding gut microbiota interactions with host immunity in early-life and the subsequent response to infection. Contrary to expectation, antibiotic exposure in early-life reduced pathogen colonization in the first 3 days of infection during adulthood in male mice and this was associated with reduced inflammatory response relative to non-antibiotic-treated, infected mice. Despite these unexpected outcomes, the impact of these results are important for future scientific research into the gut microbiota and immunology. The complexity of the gut microbiota coupled with the complexity of the immune system may drive differential responses to challenges such as infections at different ages, with different levels of exposure and between sexes. These data highlight important sex differences in microbiota-driven responses to infection, whereby differential effects were only seen in males, whilst challenging basic assumptions about antibiotic-driven effects on immune responses. Ultimately, these data will help inform more research and awareness into sex-driven differences in microbiota-driven immune responses.