Location: Immunity and Disease Prevention Research
Project Number: 2032-51530-026-00-D
Project Type: In-House Appropriated
Start Date: Jan 18, 2019
End Date: Jan 17, 2024
Our long-term objective is to determine how dietary fiber contributes to immunological health. Our central hypothesis is that immunological health is a function of both dietary intake and the functional capability of gut microbes to respond to that diet. We will use three approaches to examine our central hypothesis: a cross-sectional Phenotyping Study, a Longitudinal Study, and a Fiber Intervention Study. Sub-objectives will be addressed by each study as follows: Objective 1 Define associations between diet and gut microbiota composition and function. Sub-Objective 1A (Phenotyping Study): Examine the association between dietary features (e.g. fiber intake), gut microbial composition (bacterial taxa) and gut microbial functional capacity. Sub-Objective 1B (Phenotyping Study): Use ex vivo culture models to examine the difference between high and low fiber groups in gut microbial functional capacity and colonization resistance to a food-borne pathogen. Sub-Objective 1C (Longitudinal Study): Determine which bacterial taxa are consistently present over time and which bacterial taxa vary and correlate with dietary patterns for each subject. Sub-Objective 1D (Intervention Study): Examine the specific effects of an inulin intervention on short term changes in composition and functional capacity of the gut microbial community. Objective 2 – Assess the association of diet and microbiota with gut health. Sub-Objective 2A (Phenotyping Study): Determine how intake of dietary fiber is associated with markers of gut health in a cross-sectional study. Sub-Objective 2B (Phenotyping Study): Determine whether dietary fiber intake and gut microbiome functional capacity are correlated with markers of gut health. Sub-Objective 2C (Longitudinal Study): Determine whether a long-term habitual low fiber diet is associated with markers of chronic gut inflammation relative to high fiber-consuming controls in a longitudinal study. Sub-Objective 2D (Intervention Study): Determine if consumption of dietary inulin reduces gut inflammation and impairs intestinal permeability when perturbed by an oral typhoid fever vaccine. Objective 3 – Determine if dietary patterns that promote gut health also promote systemic immune health. Sub-Objective 3A (Phenotyping Study): Determine if dietary features or nutritional status, gut microbial composition or functional capacity, and gut inflammation markers are associated with markers of systemic inflammation, specific immune cell types, or their level of activation. Sub-Objective 3B (Longitudinal Study): Determine if the associations identified in 3A are also seen in the baseline samples from the Longitudinal Study and determine if these associations are constant across time. Sub-Objective 3C (Intervention Study): Determine if consumption of 12 g/d inulin for 10 wk (for 4 wk before, 1 wk during and 1 wk after administration of the Vivotif® vaccine) will increase the vaccine-specific ALS IgG and IgA responses (primary endpoints), the plasma antibody, and stool IgA and T-cell responses (secondary endpoints) to the vaccine, relative to 12 g/d maltodextrin.
Our central hypothesis is that immunological health is a function of both dietary intake and the functional capability of gut microbes to respond to that diet. We will use three human studies to examine our central hypothesis: a cross-sectional Phenotyping Study, a Longitudinal Study, and a Fiber Intervention Study. The Western Human Nutrition Research Center (WHNRC) Nutritional Phenotyping Study is a cross-sectional study of healthy adults balanced by sex, age and body mass index with the recruitment phase to be completed in 2019. We will use stool samples from this project in ex vivo culture models—stool fermentations, pathogen challenge, and intestinal cell response—to address how the microbial environment interacts with substrate and how it affects physiology. The WHNRC Longitudinal Study is an observational cohort of middle-aged non-obese human participants selected at baseline to have adequate or low fiber intake. This cohort will be followed for up to 20 years, subject to renewal, with baseline and year 1 occurring in the current project cycle. Primary outcomes are measures of gastrointestinal and systemic inflammation. The WHNRC Fiber Intervention Study is a randomized controlled trial designed to test whether dietary inulin improves response to an oral vaccine that includes a live attenuated enteric pathogen. To address the hypothesis that dietary fiber consumption is associated with altered gut microbiome composition and function, stool samples from the studies will be sequenced for DNA content. Stool samples from the Phenotyping Study will additionally be assessed for fermentation capability, and pathogen resistance. To address the hypothesis that dietary fiber consumption is associated with altered gastrointestinal health, stool samples from the studies will be assessed for markers of inflammation and tested in an in vitro culture model of intestinal epithelial cells. In the intervention trial, intestinal permeability will be measured by quantifying the permeability of non-metabolizable sugar molecules. To address the hypothesis that dietary fiber consumption is associated with altered systemic immunity, blood samples from the studies will be assessed for measures of innate and adaptive immunity. These include plasma markers and complete blood count (CBC) in all trials as well as flow cytometry and ex vivo cytokine production by PBMC in the Phenotyping Study and measurement of vaccine-specific lymphocyte and antibody responses in the Intervention Study. Both gastrointestinal and systemic response will also be analyzed with gut microbiota as a mediator to determine whether these responses are microbiota-dependent. The most challenging aspect of all of these studies is the recruitment and retention of human participants, particularly for the Longitudinal Study. If we are unable to recruit enough participants, we may pursue new partnerships (e.g. UC Davis alumni association) or open a second study site (e.g. Sacramento). If we are unable to retain enough participants, we could consider the subset of outcomes that can be assessed remotely or backfill by recruiting more participants.