Ontogeny of class II antigen expressing cells in rat incisor pulp

Class II antigen expressing cells are generally associated with the early phase of the immune response. Dendritic cells and macrophages expressing these cell surface antigens have recently been demonstrated and characterized in the dental pulp. The present study was undertaken to determine when the pulp receives its immunologic defense potential by examining the temporal appearance of class II antigen expressing cells in the rat incisor pulp. Pulp tissue specimens obtained at various time periods from a gestational age of 16 days to 14 wk after birth were examined by immunohistochemistry using O x 6 as a primary antibody and the ABC-technique. Comparisons were made with tissue samples from the spleen, intestine, skin and oral mucosa. At birth, all tissues, except for the pulp, presented cells expressing class II antigen with a dendritic appearance in a number and orientation resembling the mature tissue. A complete distribution of these cells was not seen in the dental pulp until 7 weeks following birth. Data show that the dental pulp acquires its ultimate structural arrangement of immune cells later than other tissues.