Differential conditioning of mucosal and systemic DCs by secretory IgA in complex with the commensal bacterium Lactobacillus rhamnosus

The intestinal cross-talk between commensal bacteria and dendritic cells (DCs), as well as local IgA production, are essential characteristics ensuring gut homeostasis. However, the effect of secretory IgA (SIgA) on commensal-DCs interaction has not been addressed yet. In this study, we analyzed the impact of the commensal representative Lactobacillus rhamnosus (LPR), alone or associated with SIgA, on mucosal and systemic DCs freshly recovered from mouse Peyer’s patches (PPs), mesenteric lymph nodes (MLNs) and spleen. Exposure of LPR to mucosal DCs conditioned these latter to exhibit anti-inflammatory and regulatory profiles characterized by: low surface expression of co-stimulatory markers; higher anti-/pro-inflammatory cytokine production ratios; promotion of regulatory T cells priming; increased expression of vitamin A-metabolizing enzyme and of TLR pathway regulatory proteins. Association with SIgA further promoted the anti-inflammatory/regulatory LPR-induced conditioning of mucosal DCs, particularly in PPs. In contrast, splenic DCs were activated when exposed to LPR, a feature dampened with SIgA. These data suggest that in addition to DCs origin and bacterial stimuli, SIgA may contribute to the regulation of immune processes after association with commensal bacteria. We conclude that commensal-SIgA immune complexes found in PPs could modulate mucosal DC functions towards a tolerogenic status prone to maintenance of intestinal homeostasis.