The oral mucosa is well known to be rich in dendritic cells (DCs), and the cervical lymph nodes (CLNs) are the draining lymph nodes for the oral mucosa. DCs play a crucial role in the induction of primary T cell-dependent immune responses. Upon uptake of antigens on the oral mucosal surface, immature DCs in the oral mucosa are thought to migrate to the regional CLNs. The oral mucosa is a potential route for vaccine administration. We examined the efficacy and some candidate biomarkers of the clinical responses to sublingual immunotherapy (SLIT) with a cedar pollen extract against cedar pollinosis. We found that Lactobacillus KW3110 administered sublingually migrated to the CLNs, and was effective for decreasing the IgE production and nasal symptoms induced by antigen provocation. Through simultaneous stimulation with antigen, improved efficacy of SLIT may be achieved by an adjuvant with oral mucosal administration of Lactobacillus KW3110.