Direct regulatory immune activity of lactic acid bacteria on Der p 1–pulsed dendritic cells from allergic patients

Lactic acid bacteria (LAB) are suggested to play a regulatory role in the development of allergic reactions. However, their potential effects on dendritic cells (DCs) directing the immune polarization remain unclear. The immunologic effect of Lactobacillus plantarum NCIMB 8826 (LAB1) on monocyte-derived dendritic cells (MD-DCs) from patients allergic to house dust mite was evaluated. MD-DCs were stimulated for 24 hours with the related allergen Der p 1 in the presence or absence of LAB1. Cell-surface markers were assessed by means of FACS analysis, and the key polarizing cytokines IL-12 and IL-10 were quantified. The subsequent regulatory effect of pulsed MD-DCs on naive or memory T cells was evaluated by determining the T-cell cytokine profile. LAB1 induced the maturation of MD-DCs, even if pulsed with Der p 1. Interestingly, after incubation with LAB1 and Der p 1, MD-DCs produced higher amounts of IL-12 than Der p 1–pulsed DCs. Indeed, the T H2 cytokine (IL-4 and IL-5) production observed when naive or memory autologous T cells were cocultured with Der p 1–pulsed MD-DCs was highly reduced in the presence of LAB1. Finally, in contrast to naive or memory T cells exposed once to Der p 1–pulsed DCs, T cells stimulated by MD-DCs pulsed with Der p 1 and LAB1 failed to produce T H2 cytokines in response to a new stimulation with Der p 1–pulsed DCs. Thus in the presence of LAB1, MD-DCs from allergic patients tend to reorientate the T-cell response toward a beneficial T H1 profile.