The role of the macrophage in collagen resorption during chronic inflammation. A new look at an old hypothesis

Cellular roles in physiological root resorption of deciduous teeth in the cat

This study has attempted to assess the importance of mesenchymal cells, fibroblasts, cementoblasts, and mononuclear phagocytes (i.e., macrophages) in physiological root resorption of feline deciduous teeth. Deciduous incisors of three- to six-month-old kittens undergoing root resorption were investigated by means of electron microscopy. In an early phase of root resorption, the resorption organ consisted of many fibroblasts and relatively few macrophages and odontoclasts, the last with a wide, clear zone and narrow, immature, ruffled border. In the active phase of root resorption, the resorption organ contained many odontoclasts with a well-developed ruffled border and a reduced clear zone, cementoblasts, fibroblasts, macrophages, neutrophils, and many blood vessels. Cementoblasts were present usually on the resorbing dentin surface adjacent to odontoclasts and, in many cases, these cells communicated with each other via gap junctions. Cementoblasts frequently extended broad cell processes with secretion granules and with phagosomes containing collagen fibrils into the dentinal tubules exposed to resorption lacunae. Some macrophages exhibiting a clear zone-like structure also appeared on resorbing dentin surfaces. In the resting phase of root resorption, the dentin surface was covered mostly with cementoblasts resembling bone lining cells. There was an occasional macrophage, but no odontoclasts were observed during this phase. During removal of the periodontal ligament concomitant with root resorption, many fibroblasts phagocytosed mature collagen fibrils, as well as amorphous fluffy material. These results suggest that these mesenchymal cells, as well as odontoclasts, are essential for the cellular removal of dental hard and soft tissues during shedding of feline deciduous teeth.

Degradation of metal-labeled collagen implants: ultrastructural and X-ray microanalysis

Three different metal salts, silver nitrate, uranyl acetate and lead citrate, are mixed with a collagen gel to produce 3 metal/collagen sponges. These sponges were implanted subcutaneously in the rat and samples harvested after 5 days of implantation. TEM observation shows that sponges are degraded and digested by macrophages, polymorphonuclear cells (PMN) and fibroblasts. We have observed that the location of the precipitates differs according to the metal added to the collagen. Lead precipitates stay longer on the collagen mesh while silver precipitates, after 5 days, are soon digested and are found in phagosomes of macrophages. Uranium precipitates are digested with the collagen and uranium/collagen associated pictures are seen in phagolysosomes. Metal precipitates accumulated in phagolysosomes of macrophagic cells are recognized by X-ray microanalysis. The degradation process of implanted collagen is discussed.

Macrophage chemotaxis in experimental tooth movement in the rat

Extracts from tissue surrounding teeth being moved contained chemotactic activity for peritoneal exudate cells (PEC). The tissue was homogenized, extracted and diafiltered using a 100,000 mol. wt cut-off filter. The filtrate contained statistically-significant chemotactic activity, whereas the retentate did not. Further fractionation of the filtrate using an isoelectric focusing column produced a filtrate fraction in the pH range between 5.0 and 6.8 which was chemotactically active. This sample was analysed for purity and mol. wt using sodium dodecylsulphate polyacrylamide-gradient gel electrophoresis (SDS-PAGE). Gels of the active fraction stained with Coomassie blue showed two distinct bands with molecular weights of 69,000 and 60,000.

Effect of dexamethasone, indomethacin, and lipopolysaccharide on the secretion of interstitial collagenase and type V collagenase by cultured macrophages

The rabbit alveolar macrophage secretes at least two collagenolytic metalloproteinases in vitro including an interstitial collagenase and a type V collagenase. Using assays previously shown to discriminate between these two activities, the secretion of these two enzyme activities was investigated. Both enzyme activities accumulated in culture over 11 days and the release of both were similarly inhibited by cycloheximide. Collagenolytic activity was negligible in cell lysates. The interstitial collagenase was found in a latent form but the type V collagenase activity was active in the culture medium. When cultured in the presence of dexamethasone, the secretion of both the enzymes were identically inhibited in a dose-dependent manner. Indomethacin was an effective inhibitor of secretion of both collagenases at a concentration of 10(-5) M but not at lower concentrations. Finally, bacterial lipopolysaccharide stimulated the secretion of both type V and interstitial collagenase by these cells. These studies indicate that, like the interstitial collagenase, the type V collagenase is released from the cell as synthesized and is not stored intracellularly. Protein synthesis is necessary for the release of both these collagenases. Furthermore, the release of type V collagenase responded to dexamethasone, indomethacin, and lipopolysaccharide in a manner identical to the secretion of the interstitial collagenase suggesting that synthesis and secretion of these two enzymes are regulated in a similar manner.

A stereologic analysis of collagen phagocytosis by fibroblasts in three soft connective tissues with differing rates of collagen turnover

The purpose of this study was to assess the importance of the phagocytic mechanism of collagen resorption in the normal turnover and remodelling of soft connective tissues. Collagen phagocytosis by fibroblasts in rat skin, attached gingiva, and periodontal ligament was quantitated using the methodology of electron microscopic stereology. Periodontal ligament contained five and 15 times as much phagocytosed collagen as attached gingiva and skin respectively. Also, for each tissue examined, a positive correlation was observed between the amount of collagen phagocytosed and the known rate of mature collagen turnover.