An Immunohistochemical Study of Matrix Components in Early-Stage Vascular Canals Within Mandibular Condylar Cartilage in Midterm Human Fetuses.

Matrix components of vascular canals (VCs) in human fetal mandibular condylar cartilage (15-16 weeks of gestation) were analyzed by immunohistochemistry. Prevascular canals (PVCs), consisting of spindle-shaped cells without capillary invasion, were observed within the cartilage. Intense immunoreactivity for collagen type I, weak immunoreactivity for aggrecan and tenascin-C, weak hyaluronan (HA) staining, and abundant argyrophilic fibers in PVCs indicated that they contain noncartilaginous fibrous connective tissues that was different from those in the perichondrium/periosteum. These structural and immunohistochemical features of PVCs are different from those of previously reported cartilage canals of the long bone. Capillaries entered the VCs from the periosteum and ascended through VCs. Following capillary invasion, loose connective tissue had formed in the lower part of VCs, and immunoreactivity for collagen types I and III, tenascin-C, and HA staining was evident in the matrix of loose connective tissue. No chondroclasts or osteogenic cells were seen at the front of capillary invasion, although small, mononuclear tartrate-resistant acid phosphatase (TRAP)-positive cells were present. Meanwhile, TRAP-positive, multinucleated chondroclasts and flattened, osteoblast-like cells were observed in the loose connective tissue at the lower part of VCs. These results may indicate slow progress of endochondral ossification in human fetal mandibular condyle. Further, unique matrix components in PVCs/VCs, which were different from those in cartilage canals in long bone, may reflect the difference of speed of endochondral ossification in cartilage canals and human fetal mandibular condyles.