Immunomodulatory effect of Lacticaseibacillus rhamnosus and Lactobacillus acidophilus in human dendritic cells

This study explored the immunomodulatory properties of the probiotic strains Lacticaseibacillus rhamnosus LR-32 and Lactobacillus acidophilus LA-5 by evaluating their effects on human dendritic cell (DC) responses. Immature DCs were obtained from human CD14⁺ monocytes and challenged with E. coli LPS and/or probiotic lactobacilli at a DC ratio of 1:10. Relative transcription of inflammatory mediators and pattern-recognition receptors was assessed by RT-qPCR. Cytokine production and surface marker expression were evaluated by ELISA and flow cytometry, respectively. DC function was further assessed after interaction with CD4⁺ T lymphocytes, followed by analysis of T cell phenotype by flow cytometry and cytokine production by ELISA. LPS upregulated the transcription of intracellular receptors AIM2, NOD1, and NOD2 and increased COX-2, TNF-α, IL-1β, IL-6, CXCL-8, IL-12, and IL-18 mRNA levels compared with immature DCs (p < 0.001). Exposure to probiotics downregulated most genes encoding receptors and inflammatory mediators compared with LPS-stimulated DCs. In LPS-stimulated DCs, LA-5 reduced intra- and extracellular receptor gene expression, increased COX-2, TNF-α, IL-1β, IL-6, CXCL-8, and IL-10 transcription, and decreased IL-12 mRNA levels. LR-32 upregulated TLR2, COX-2, IL-6, CXCL-8, and IL-10, while reducing IL-12 expression, although these effects were less pronounced than those induced by LA-5. LA-5-exposed DCs induced a higher frequency of CD25highFOXP3highCD127low CD4⁺ T cells than LR-32. These findings indicate that LA-5 and LR-32 modulate human DC responses in a strain-dependent manner. Rather than acting as broadly anti-inflammatory stimuli, these probiotics reshaped LPS-induced activation by modulating pattern-recognition receptor pathways, cytokine responses, and a Treg-associated CD4⁺ T cell phenotype, suggesting a potential role in controlled mucosal immune regulation.