Dental caries and pulpitis are the most common bacterial infections in humans. However, the immune responses against bacterial stimulation in dental pulp that is bounded by special hard tissues are poorly understood. We examined the initial immune responses in mouse dental pulp after cusp trimming and acid treatment. Using fluorescence immunohistochemistry, two distinct cell populations were identified in the intact pulp; CD11c+F4/80- and CD11c-F4/80+ cells. CD11c+F4/80- cells were localized in the pulp-dentin (P-D) border of the central pulp beneath the dental fissure, whereas CD11c-F4/80+ cells with dendritic morphology were distributed in the perivascular region of the inner pulp and the sub-odontoblastic layer. CD11c+F4/80- cells, but not CD11c-F4/80+ cells, constitutively expressed toll-like receptors 2 and 4 and CD205, and migrated to the P-D border of the treated side within 2 h after the treatment. In parallel, some of the F4/80+ cells migrated to the inner pulp of the treated side, increased in size and enhanced CD86 expression. At 24 h, the CD86+ cells with high fluorescence intensity had disappeared entirely from the pulp. Concurrently, CD86high cells expressing intermediate levels of CD11c and high levels of MHC class II and F4/80, assessed by using flow cytometry, increased significantly in the regional lymph nodes, suggesting migration of these cells from the dental pulp. Our results are the first to demonstrate the existence of at least two types of dendritic cells (DCs) in dental pulp. The CD11c+ sentinel and F4/80+ interstitial DCs might have distinct territories and unique roles in responding to external stimuli via the dentinal tubules.