Immune responses triggered by oral antigens can have significant clinical consequences. Dendritic cells (DCs) are among the most important cellular determinants of oral tolerance, as they are tasked, in a mucosal environment that also contains antigens and pattern stimuli derived from vast commensal microbiota, with deciding whether adaptive immunity should be mobilized or tolerized to given antigens. We have recently generated a DC-specific mouse model of spontaneous Th2-associated disease of the small intestine (SI) called TRAF6?DC, which initially appeared to be microbiota-dependent because antibiotic treatment is ameliorative. However, germ-free (GF) TRAF6?DC mice surprisingly exhibit exacerbated disease compared to mice housed under specific pathogen-free (SPF) conditions, suggesting a trigger other than microbiota. We now have preliminary findings that TRAF6?DC disease is completely ameliorated in mice fed antigen-free (AF) diet, suggesting the driving stimulus of disease is food antigen. The TRAF6?DC model may be employed to reveal novel mechanisms underpinning DC-mediated oral tolerance, and thus we propose the following specific aims: 1. Investigate the immunological mechanisms of TRAF6?DC oral antigen sensitivity. We propose to further characterize the immunologic abnormalities of TRAF6?DC mice in the context of oral antigen sensitivity to elucidate novel immunologic mechanisms linking development and maintenance of oral tolerance to TRAF6-mediated signals in DCs. In this respect, we will examine the relevant cellular actors, as well as regulatory and effector molecules to determine how homeostasis is disrupted in the presence of oral antigen. We will use diphtheria toxin receptor (DTR) transgenic mice to examine the effects of temporal ablation of various types of DCs in the context of both DC-specific TRAF6 deficiency and oral tolerance maintenance to begin to determine whether TRAF6 provides key pro-tolerance signals to certain cell types versus creating dysfunctional DCs in its absence. Model oral antigen will also be utilized in TRAF6?DC mice to better define the mechanism(s) of disease development. 2. Investigate the independent effects of microbiota and antibiotics on TRAF6?DC oral antigen sensitivity. Mitigation of TRAF6?DC disease by antibiotics in the absence of microbiota suggests potential biologically relevant direct effects of antibiotics on immune cells which we propose to investigate in the context of TRAF6?DC oral antigen sensitivity in the presence or absence of microbiota and/or food antigens. While we typically employ a broad-spectrum cocktail of four antibiotic drugs from different classes for the purpose of microflora depletion, our hypothesis in these studies will initially focus on the role of ampicillin, which belongs to the ?-lactam class that has been previously reported to have direct biotic immunomodulatory activity. Additionally, we will examine the effects of antibiotics on oral antigen sensitivity in TRAF6?DC neonates under SPF and GF conditions to determine temporal relationships between antibiotic treatment, commensal microbiotic colonization, and oral antigen sensitivity.

Public Health Relevance

Dendritic cells (DCs) are found in the mucosal tissues that line the intestine and are essential for maintaining immune tolerance against both commensal microbiota and oral antigens. As such, studying how DC functions are regulated is critical to understanding the mechanistic underpinnings of immune regulation.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Innate Immunity and Inflammation Study Section (III)
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Rothermel, Annette L
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University of Pennsylvania
Schools of Medicine
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Walsh, Matthew C; Takegahara, Noriko; Kim, Hyunsoo et al. (2018) Updating osteoimmunology: regulation of bone cells by innate and adaptive immunity. Nat Rev Rheumatol 14:146-156