Background. Dendritic cells regulate immune responses to microbial products and play a key role in ulcerative colitis (UC) pathology. We determined the immunomodulatory effects of probiotic strainLactobacillus caseiShirota (LcS) on human DC from healthy controls and active UC patients.Methods. Human blood DC from healthy controls (control-DC) and UC patients (UC-DC) were conditioned with heat-killed LcS and used to stimulate allogeneic T cells in a 5-day mixed leucocyte reaction.Results. UC-DC displayed a reduced stimulatory capacity for T cells (P<0.05) and enhanced expression of skin-homing markers CLA and CCR4 on stimulated T cells (P<0.05) that were negative for gut-homing markerβ7. LcS treatment restored the stimulatory capacity of UC-DC, reflecting that of control-DC. LcS treatment conditioned control-DC to induce CLA on T cells in conjunction withβ7, generating a multihoming profile, but had no effects on UC-DC. Finally, LcS treatment enhanced DC ability to induce TGFβproduction by T cells in controls but not UC patients.Conclusions. We demonstrate a systemic, dysregulated DC function in UC that may account for the propensity of UC patients to develop cutaneous manifestations. LcS has multifunctional immunoregulatory activities depending on the inflammatory state; therapeutic effects reported in UC may be due to promotion of homeostasis.