Cells and Materials


The tissue response to implanted hydroxyapatite (HAP) in rat alveolar bone was investigated using morphological and cytochemical approaches. High-resolution immunogold labeling was used to examine the distribution of two non-collagenous bone proteins, osteopontin and osteocalcin, and two plasma proteins, a2HSglycoprotein (fetuin) and albumin. Glycoconjugates were characterized by lectin-gold cytochemistry using Ricinus communis I agglutinin and Wheat germ agglutinin. Transmission electron microscopy demonstrated the presence of an electron-dense, lamina limitans-like layer at the HAP particle-bone interface and organic material within the micropores of the particles. Mineral was observed in relation to both these sites. The HAP particle-bone interface was strongly immunoreactive for osteopontin; moderately to weakly reactive for osteocalcin, a 2HS-glycoprotein and albumin, and rich in glycoconjugates containing galactose and/or N-acetyl-glucosamine/sialic acid. Organic material within the micropores of the HAP particles was also labeled with the various antibodies and lectins. These results indicate that the lamina limitans at the HAP particle-bone interface is enriched in osteopontin as well as in sugars present in this and other molecules. Similarly, certain bone and plasma proteins infiltrate the micropores of HAP and distribute differentially throughout the particles.