Even though the immunopathogenic triggering event(s) in type 1 diabetes (T1D) remain enigmatic, there is accumulating evidence, mainly in rodent models of the disorder, suggesting that pancreas-resident antigen-presenting cells (APC) are activated very early post-natally. This results in the recruitment of innate immune cells like neutrophils into the pancreas even before adaptive immune cells that are islet antigen-specific are detected. Activated neutrophil accumulation into new-onset T1D human pancreata has also been documented. While it is possible that this innate immune activation very early-on reflects a reparative response to some endogenous natural post-natal “remodeling” process gone-astray, or to the incursion of viruses, the direct associations have not been conclusively established. The kinetics of the activation of resident APC and the post-natal aggravation of innate immunity prior to any signs of T-cell incursion is better associated with pattern recognition receptor-mediated signals, implying a bacterial response. Indeed, the NOD/ShiLtJ mouse strain as well as human T1D patients, have been shown to exhibit a “leaky gut” phenomenon and treatment of NOD mice with antibiotics or an exchange of the gut microbiota has resulted in prevention of disease onset. Furthermore, microbiota from the “leaky gut” have been shown to localize inside the pancreas, triggering an inflammation. In spite of recent studies aimed at identifying specific microbes as triggers, there is no evidence pointing to a specific pathogen. Our hypothesis, instead, proposes that any bacterial pathogen can trigger the resident APC through the formation of biofilms. Bacterial biofilms are omnipresent in tissues in which bacteria reside and act not-too-unlike extracellular trap structures. These highly pro-inflammatory microenvironments compel tissue repair and remodeling. Biofilm constituent molecules not only protect and promote the survival of entrapped bacteria, but also act as “danger” signals to the pancreas-resident APC. Biofilm formation, consequent to post-natal “leaky gut”-facilitated bacterial deposition inside the pancreas is hypothesized to trigger the resident APC, to attract neutrophils and migratory macrophages and dendritic cells, provoking an inflammation that ultimately culminates in the activation of autoreactive lymphocytes inside the pancreas-draining lymph nodes. The objective of this study, using nPOD human pancreas tissue, is to first demonstrate the existence of bacterial biofilms inside the pancreas of T1D subjects. Then, to compare the incidence of biofilms in the T1D pancreata to non-diabetic pancreata and to determine any associations of biofilm presence, density, and “signature” with age-at-onset of disease. In parallel, we will determine if the presence of biofilms and/or specific signatures, is associated with the presence of particular innate immune cell populations and their state of activation in situ. To realise these objectives experimentally, we will deploy multiparameter immunofluorescence microscopy to identify specific immune cell populations; fluorescence in situ hybridization to identify biofilms, and sequencing technology to identify biofilm signatures in the pancreas tissues. On its own, we believe that this project is novel since it is the first-in-kind to explore the potential involvement of biofilms in organ-specific autoimmunity, and it can also inform a better understanding of the initiating trigger of T1D altogether.
