Mucosal-associated invariant T (MAIT) cells are T lymphocytes with a key role in immune surveillance. Riboflavin derivatives produced by the gut microbiota are MAIT cell ligands(Reference Patel, Kjer-Nielsen and Le Nours1). Evidence suggests that unknown metabolites synthesised by probiotic strains modulate MAIT cell function(Reference Johansson, Bjorkander and Mata Forsberg2,Reference Hinks3) . Galactooligosaccharides (GOS) are prebiotics produced via transgalactosylation by β-galactosidases, which are expressed by gut bacteria(Reference Grimaldi, Swann and Vulevic4). We aim to assess whether GOS modulate the function of MAIT cells or other peripheral blood mononuclear cell (PBMC) subsets and whether cells respond differently to a riboflavin derivative in presence of GOS.
Healthy PBMCs (n = 8) were cultured for 20 h with GOS (Bimuno®) (12 mg/mL), or a riboflavin derivative (5-A-RU 0.18 μM + methylglyoxal 1 μM), or co-stimulated with both. Unstimulated cells were used as control. One-way ANOVA or Kruskal-Wallis test followed by Bonferroni's or Dunn's post-hoc test were performed depending upon data distribution.
Treatment with GOS did not affect viability. PBMCs incubated with GOS presented lower CD4 expression on T helper cells (MFI 14,561 ± 612.3 vs 17,593 ± 2,157; p = 0.0053) and secreted more IL-8 (104.0 ± 62.9 ng/mL vs 3.8 ± 2.6 ng/mL; p = 0.0005) compared to control. Intracellular staining revealed that monocytes were responsible for the upregulated IL-8 expression. Co-treatment of cells with the riboflavin derivative and GOS resulted in decreased CD69 expression by lymphocytes (MFI 19,076 ± 2,648 vs 15,761 ± 1,158 p = 0.0017), T cells (MFI 20,317 ± 2,303 vs 16,572 ± 1,439 p < 0.0001) and cytotoxic T cells (MFI 24,669 ± 4,249 vs 20,188 ± 3,485 p = 0.0205) compared to riboflavin derivative alone, and in lower % MAIT cells expressing IL-17A vs riboflavin derivative alone (0.03 ± 0.03 vs 0.49 ± 0.40 p = 0.0008).
Overall, GOS showed immunomodulatory effects, including the modulation of CD4 expression and enhancement of IL-8 secretion. PBMCs responded differently to ligand challenge in presence of GOS, suggesting that the prebiotic may interfere with riboflavin metabolites or signal via similar pathways.
Acknowledgements
GOS (Bimuno®) was provided by Clasado Biosciences
