Abstract
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.