Degradation of the Cartilage by Mononuclear Cells in the Course of Ossification
Acta Veterinaria Brno
Cerny H.: Degradation of the Cartilage by Mononuclear Cells in the Course of Ossification. Acta vet. Brno, 53, 1984: 3-17. Morphology of the destructive phase of endochondral ossification was studied in the metaphyseal rim of the growth cartilage of the tuber coxae using 17 bovineindividuals from 241 d fetal age to 3.5 yr. The material was routinely processed for electron microscopy. Our attention was focused on the role of the mononuclear cell in the process of degradation of the cartilaginous
... f the cartilaginous model in the course of ontogenetic development. The electron-microscopic picture showing the cellular effects on the mineralized ground substance revealed endothelial cells of the penetrating blood capillaries, pericapillary clastic cells and free macrophages of hematogenic origin interposed between the wall of blood capillaries and ground substance of the cartilage participating in this process in the course of capillary invasion. In cattle, mononuclear clastic cells play a major role in destruction of the cartilaginous model being located in the erosion line and in the osteoid zone. In the course of ontogenetic development the numbers of the individual cell types are changing. Whereas in the prenatal period capillary resorption and activity of peri capillary cells prevail, in the postnatal period of ossification free blood macrophages form the majority of cells involved. Attacking of the mineralized ground substance by mononuclear clastic cells results in its degradation consisting of solubilization, fragmentation, phagocytosis and combined resorption. Degradation of the cartilaginous model connected with resorption of the ground substance is a complex process. It is the result of cells effect on the cartilage during which several mechanisms are operating simultaneously. The most effective mechanism of degradation is fragmentation resulting in substantial enlargement of the active surface. Larger fragments undergo further fermentation. These fragments are solubilized from the periphery of the ground substance to the centre and the smallest fragments are phagocytized by the macrophages. The final effect of cellular activity is complete solubilization of the ground substance and its resorption from the pericapillary space. Cattle, ontogenesis, ossification, degradation of the cartilage, resorption, mononuclear cell. Effects exerted by mononuclear cells on mineralized cartilage matrix have received rather limited attention in literature. As early as 1970 Irving and Heeley suggested that two different cell types participate in the osteoclastic resorption. Using an autoradiographic method with 3H-proline-labelling for organic structures they demonstrated that non-labelled inorganic material was phagocytized by osteoclasts whereas the labelled organic material was destroyed by mononuclear cells. These data seem to indicate that osteoclasts cannot destroy the organic matrix.