Gut microbiota and immune response under chronic social stress in an LPS-induced inflammatory model

Chronic psychological stress is a known modulator of immune responses and gut microbiota composition. However, its impact on the host's inflammatory response to leptospiral lipopolysaccharide (LPS) remains insufficiently studied. This study aimed to evaluate how chronic social stress alters immune gene expression and gut microbiota composition in a rat model of leptospiral LPS-induced systemic inflammation. Male Wistar rats were divided into control (<i>n</i> = 6), LPS-induced inflammation group (<i>n</i> = 6), and LPS-induced inflammation group with chronic stress group (<i>n</i> = 12). Inflammation was induced by intraperitoneal injection of LPS from <i>Leptospira interrogans</i> (10 mg/kg). Chronic social stress was applied through 14-day overcrowding. Gene expression in peripheral blood was analyzed using RT² Profiler PCR Arrays, and gut microbiota composition was evaluated via culture-based quantification of selected taxa. Data were analyzed using Student's t-test, Kruskal-Wallis test with Dwass-Steel-Critchlow-Fligner post hoc comparisons, PCA, and Spearman's correlation. LPS administration significantly upregulated six immune-related genes compared to controls, including <i>Il6</i>, <i>Il1b</i>, <i>Ifng</i>, <i>Il10</i>, <i>Ccl3</i>, and <i>Ccl5</i> (log₂FC ≥ 2, <i>p</i> < 0.05). In the LPS+Stress group, only <i>Il10</i> and <i>Tnf</i> remained significantly upregulated above the same threshold. Principal component analysis (PCA) revealed distinct clustering of the gut microbiota profiles between the experimental groups. Significant alterations were found in the relative abundance of <i>Bifidobacterium</i><i>spp.</i>, <i>Lactobacillus</i><i>spp.</i>, <i>Klebsiella</i> <i>spp.</i>, <i>Morganellaceae</i>, and <i>Alcaligenes faecalis</i>. Notably, <i>Klebsiella</i><i>spp.</i> abundance positively correlated with <i>Il1b</i> expression in both LPS (<i>r</i> = 0.613, <i>p</i> = 0.0342) and LPS+Stress groups (<i>r</i> = 0.663, <i>p</i> = 0.0188), while <i>Alcaligenes faecalis</i> abundance correlated with <i>Tnf</i> expression in the LPS+Stress group (<i>r</i> = 0.616, <i>p</i> = 0.0330). Chronic social stress modifies the leptospiral LPS-induced immune response and contributes to significant alterations in gut microbiota. The observed correlations between specific microbial taxa and proinflammatory gene expression indicate microbiota-immune interactions that may underlie stress-associated changes in systemic inflammation.