Appearance and distribution of dendritic cells and macrophages in dental pulp during early postnatal morphogenesis of mouse mandibular first molars.

Dendritic cells and macrophages were examined in dental pulp during the postnatal development of mouse mandibular first molars, by immuno- and enzyme histochemistry. F4/80 antibody against dendritic cells and macrophages demonstrated labeled cells predominantly in and around the odontoblastic layer during tooth development from postnatal day 0 (PN0) to PN5. Labeling with Mac-1, Mac-2, and MOMA-2 antibodies against macrophages showed varied distribution patterns. Mac-1-positive cells were not detected in the dental pulp. Mac-2-positive cells appeared in the dental pulp at PN0, but not in or around the odontoblastic layer, and disappeared by PN3. A few MOMA-2-positive cells were detected in the dental pulp during the period examined. The F4/80-positive cells in and around the odontoblastic layer did not exhibit acid phosphatase or non-specific esterase activities. In addition, the F4/80-positive cells showed continued expression of Fcgamma receptor, but not class II major histocompatibility complex (MHC). Other antibodies against dendritic cells (NLDC-145, MIDC-8, and 33D1) did not label the F4/80-positive cells. We concluded that the F4/80-positive and class II MHC-negative cells in and around the odontoblastic layer may be immature dendritic cells in the early stages before eruption, weaning, and crucial exposure to antigenic stimuli. They may not only act primarily as immunosurveillance cells, but also play a role in a regulatory function and differentiation of odontoblasts.

Collagen-phagocytosing ability of periodontal osteoblasts at the bone surface.

The collagen-phagocytosing activity of osteoblasts at the alveolar bone-ligament interface of rat mandibular first molars was investigated both histologically and histochemically. Alveolar bones of male Wistar rats (6 months old) were used in this study. Collagen-containing phagosomes appeared in cuboidal osteoblasts aligned on the bone surface. The 5.7% of the osteoblasts exhibiting alkaline phosphatase activity revealed collagen-containing phagosomes, and the collagen fibrils within the phagosomes were at various stages of degradation. In addition, acid phosphatase activity and the immunocytochemical distribution of cathepsin B were found in these collagen-containing phagosomes at similar locations. The presence of both enzymes in the phagosomes suggests that an intracellular degradation of collagen occurs. Therefore, in addition to the osteoblastic functions of synthesizing and secreting bone matrices, osteoblasts are also capable of phagocytosis and the intracellular disintegration of collagen. Our findings suggest that osteoblasts at the alveolar bone-periodontal ligament interface have a collagen-phagocytosing ability and play an important role in the physiological remodeling and metabolic breakdown of collagen fibrils of periodontal ligament without osteoclastic bone remodeling.

Effects of running exercise on the mandible and tibia of ovariectomized rats.

To examine the effects of running exercise on the mandible and tibia of ovariectomized (OVX) rats, 26-week-old sham-operated (Sham) and OVX rats 1 week post-ovariectomy were subjected to non-exercise (Sham-Cont and OVX-Cont) and exercise (Sham-Exc and OVX-Exc) for 8 weeks. OVX induced a significant decrease in alkaline phosphatase (ALP) and an increase in tartrate-resistant acid phosphatase (TRAP) activity and a reduction of 17beta-estradiol in the serum. In OVX-Cont rats, histology and bone mineral density (BMD) showed bone loss in the proximal tibia, and histology, soft X-ray photographs and bone marrow area (BMA) revealed enlargement of the bone marrow cavity in the neck of the condylar process. In OVX-Exc rats, exercise significantly increased ALP activity, decreased TRAP activity and markedly elevated serum progesterone levels. Histology and BMD in the tibia and histology, X-ray photographs and BMA in the mandible were comparable to those in Sham rats. In Sham-Exc rats, unexpected decreases were observed in serum enzymes and hormones, but the histology and BMD in the tibia and histology, X-ray photographs and BMA in the mandible were very similar to those in Sham-Cont rats, suggesting a decrease of bone turnover with no change of bone mass in the tibia and mandible. We conclude that exercise has a beneficial effect not only on bone loss in the tibia, but also on differential changes in the neck of the condylar process, perhaps by increasing serum levels of progesterone in OVX rats.