Immunomodulatory activity of Lacticaseibacillus rhamnosus R0011: analysis of secretome-mediated impacts on innate immune outcomes in intestinal epithelial cells and antigen presenting cells
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Certain lactic acid bacteria (LAB), such as Lacticaseibacillus rhamnosus R0011, are associated with immune modulatory activities including down-regulation of pro-inflammatory gene transcription and expression. While host intestinal epithelial cells (IECs) and antigen-presenting cells (APCs) can interact directly with both commensal and pathogenic bacteria through innate immune pattern recognition receptors, recent evidence indicates indirect communication mediated by soluble mediators may be important in shaping host immune outcomes at the gut-mucosal interface. However, many questions remain about how soluble mediators derived from LAB can influence functional immune outcomes in IECs and APCs, especially in the context of pro-inflammatory challenge as over-expression and dysregulation of the inflammatory mediators they produce also contributes to numerous inflammatory disease pathologies. Genome-wide transcriptional profiling revealed context-dependent regulation of Tumor Necrosis Factor α and Salmonella enterica subsp. enterica serovar Typhimurium secretome-induced pro-inflammatory mediator transcription and production by the Lacticaseibacillus rhamnosus R0011 secretome (LrS) in human IEC, indicating a potential for modulation of pro-inflammatory immune activity with minimal IEC impact in the absence of a pro-inflammatory challenge. This modulation may be mediated through induction of negative regulators of innate immunity (ATF3, TRIB3, DUSP1) and through changes in global histone acetylation patterns, events important in maintaining immune regulation. THP-1 human monocytes conditioned with the LrS showed functional, transcriptional, and immunometabolic signatures consistent with M2 immunoregulatory activity, with increased production of immunoregulatory cytokines IL-10, IL-1Ra, and IL-4 and a cell-surface expression profile of CD11b, CD11clo, and CX3CR1, features shared with subsets of gut macrophages. The LrS was able to attenuate STS-induced damage to IEC monolayer integrity and pro-inflammatory mediator production in Transwell co-cultures of human IECs and APCs, indicating that the LrS retains immunoregulatory activity in a context which more closely mimics that which occurs in vivo. Biochemical characterization of the soluble components found in the LrS revealed unique protein, amino acid, and metabolomic profiles warranting future experimentation to determine components with immunoregulatory bioactivity. Taken together, the results reported here provide insight into novel routes for indirect host-microbe communication mediated via secretome components and the subsequent impact on multiple immune regulatory mechanisms integral for IEC and APC function and activity.