Shifts in the gut microbiota composition, called dysbiosis, have been directly associated with acute and chronic diseases. However, the underlying biological systems connecting gut dysbiosis to systemic inflammatory pathologies are not well understood. Phospholipids (PLs) act as precursors of both, bioactive inflammatory and resolving mediators. Their dysregulation is associated with chronic diseases including cancer. Gut microbial-derived lipids are structurally unique and capable of modulating host’s immunity. Lactobacillus johnsonii N6.2 is a Gram-positive gut symbiont with probiotic characteristics. L. johnsonii N6.2 reduces the incidence of autoimmunity in animal models of Type 1 Diabetes and improves general wellness in healthy volunteers by promoting, in part, local and systemic anti-inflammatory responses. By utilizing bioassay-guided fractionation methods with bone marrow-derived dendritic cells (BMDCs), we report here that L. johnsonii N6.2 purified lipids induce a transcriptional signature that resembles that of migratory (mig) DCs. RNAseq-based analysis showed that BMDCs stimulated with L. johnsonii N6.2 total lipids upregulate maturation-mig related genes Cd86, Cd40, Ccr7, Icam1 along with immunoregulatory genes including Itgb8, Nfkbiz, Jag1, Adora2a, IL2ra, Arg1, and Cd274. Quantitative reverse transcription (qRT)-PCR analysis indicated that PLs are the bioactive lipids triggering the BMDCs response. Antibody-blocking of surface Toll-like receptor (TLR)2 resulted in boosted PL-mediated upregulation of pro-inflammatory Il6. Chemical inhibition of the IKKα kinase from the non-canonical NF-κB pathway specifically restricted upregulation of Il6 and Tnf. Phenotypically, PL-stimulated BMDCs displayed an immature like-phenotype with significantly increased surface ICAM-1. This study provides insight into the immunoregulatory capacity of Gram-positive, gut microbial-derived phospholipids on innate immune responses.

Summary: The loss of insulin secretory function associated with type 1 diabetes (T1D) is attributed to the immune-mediated destruction of beta cells. Yet, at onset of T1D, patients often have a significant beta cell mass remaining while T cell infiltration of pancreatic islets is sporadic. Thus, we investigated the hypothesis that the remaining beta cells in T1D are largely dysfunctional using live human pancreas tissue slices prepared from organ donors with recently diagnosed T1D. Beta cells in slices from donors with T1D had significantly diminished Ca ²⁺ mobilization and insulin secretion responses to glucose. Beta cell function was equally impaired in T cell-infiltrated and non-infiltrated islets. Fixed tissue staining and gene expression profiling of laser-capture microdissected islets revealed significant decreases of proteins and genes in the glucose stimulus secretion coupling pathway. From these data, we posit that functional defects occur in the remaining mass of beta cells during human T1D pathogenesis.

Background/Objectives: Lactobacillus johnsonii N6.2 is a gut symbiont with probiotic properties. L. johnsonii N6.2 delayed the progression of type 1 diabetes (T1D) in diabetic-prone rats. The probiotic intake demonstrated immune cell modulation in healthy volunteers, leading to improved wellness and fewer reported symptoms like headaches and abdominal pain. These systemic immune-modulating benefits are attributed to L. johnsonii N6.2’s bioactive fractions, including extracellular vesicles (EVs) and purified phospholipids (PLs). We have previously shown that L. johnsonii N6.2 PLs modulate dendritic cell (DC) function towards a regulatory-like phenotype. Here, we further characterize the immune regulatory effects of L. johnsonii N6.2 PLs on adaptive immunity, specifically upon DC and T cell interactions. We hypothesized that PL-stimulated DCs suppress T cell-mediated responses to maintain tolerance in intra- and extra-intestinal sites. Methods: Bone marrow-derived dendritic cells (BMDCs) were generated from Sprague-Dawley rats and stimulated with L. johnsonii N6.2 PLs. Isogenic T cells were isolated from PBMCs obtained via terminal exsanguination. In vitro cellular assays, co-culture experiments, gene expression analysis by qRT-PCR, and flow cytometry assays were conducted to assess the immune regulatory effects of L. johnsonii N6.2 PLs. Results: The PL-stimulated BMDCs upregulated DC regulatory markers and exhibited an immature-like phenotype with reduced surface expression of maturation markers but increased surface migratory molecules (ICAM-1). These BMDCs presented immunosuppressive functions upon cognate T cell interactions and in the presence of TCR stimulation. Specifically, PL-stimulated BMCDs suppressed Th1 effector function and induced the expression of T cell anergy-related genes after co-culturing for 72 h. Conclusions: This study highlights the immune regulatory capacity of L. johnsonii N6.2’s bioactive components on adaptive immunity, specifically that of purified PLs on DC:T cell-mediated responses leading to immunosuppression. Our findings suggest that L. johnsonii N6.2-purified PLs play a role in regulating adaptive immunity, offering potential benefits for managing immune-related diseases like T1D.

This research evaluates a therapeutic approach based on tissue-targeted immunomodulation with a potential broad application to treat autoimmune diseases including type 1 diabetes (T1D). We generated a bispecific immune agonist that binds beta cells and suppresses autoreactive T cells. These bispecific molecules called immune modulating monoclonal–T cell receptor (TCR) against autoimmune disease (ImmTAAI), consist of a human-specific TCR–targeting domain fused with a programmed death-1 agonist. We used live pancreas slices to demonstrate targeting of ImmTAAI molecules to preproinsulin peptide–HLA-A2 complexes on human beta cells. ImmTAAI molecules protected beta cells from T cell killing by increasing T cell motility and inhibiting effector molecule and cytokine secretion. ImmTAAI treatment also increased the motility of islet-infiltrating T cells in slices from a donor with recent-onset T1D and preserved insulin secretion in slices cocultured with T cell avatars transduced with diabetogenic TCRs. These data demonstrate that ImmTAAI molecules have the potential to limit T cell activity locally, making this an attractive platform to elicit targeted immunoregulation in T1D.

Purpose: This protocol details processing fixed paraffin sections from human pancreas for the Nanostring GeoMX digital spatial profiler (DSP) immuno-oncology proteome atlas (IPA). This technology is based upon a defined antibody panel of 575 markers. Each antibody is conjugated to an RNA probe. The RNA probes are designed with UV cleavable linkers and DSP barcodes. Fluorescent-labeled antibodies against antigens that define specific cell types were used as morphology markers. Morphology markers are used to identify cell types of interest with nuclear counterstaining permitting tissue spatial information. Sample regions of interest (ROI) are defined based on the three morphology markers and each ROI is illuminated with UV light thereby cleaving hybridized RNA probes. Cleaved probes are aspirated via microcapillary and deposited into a unique well of a 96-well collection plate. The collection plate is used for next generation sequencing (NGS). Scope: This document was written following GeoMX NGS guidelines (university.nanostring.com) with minor modifications for the University of Florida Molecular Pathology Core. The entire workflow is described for manual slide staining and GeoMX DSP instrument use. Steps for library construction, sequencing, bioinformatics, and data analysis are in outline form only. Library preparation and sequencing are outsourced to the University of Florida ICBR facility. Expected outcome: Targeted-protein quantification via bulk RNA-sequencing will be obtained from fixed human pancreas sections within regions of interest and subareas defined by cell morphology markers.

Pancreatic beta cells have the unique function of synthesizing and secreting high amounts of the inhibitory neurotransmitter γ-aminobutyric acid (GABA). The mechanism of GABA secretion, whether vesicular or channel-mediated, is debated. Our study reveals surprising temporal complexity in the pattern of islet GABA secretion. We used insulin secretion modulators to demonstrate that GABA release is not directly correlated with insulin secretion. VGAT reporter mice also showed that beta cells do not express the requisite vesicular GABA transporter (VGAT) for vesicular GABA release. Instead, GABA is secreted from the cytosol in pulses by the LRRC8A/D isoform of the volume regulatory anion channel (VRAC). We further demonstrate the dynamic coordination of GABA release with calcium influx in beta cells and dependence on beta cell depolarization. These results suggest a model where GABA is released during the peaks of beta cell calcium oscillations to provide feedback which strengthens and reinforces the oscillation waveform.