AN IMMUNOCYTOCHEMICAL STUDY FOR LYSOSOMAL CATHEPSIN-B AND CATHEPSIN-DRELATED TO THE INTRACELLULAR DEGRADATION OF TITANIUM AT THE BONE-TITANIUM INTERFACE

THE MORPHOLOGICAL RELATIONSHIP BETWEEN titanium and lysosomal proteina ses, cathepsins B and D, at the bone-titanium interface using titanium -coated plastic implants placed for 28 days in the tibiae of 6-week-ol d rats was immunocytochemically investigated by the colloidal immunogo ld-silver method. Under Light microscopy the titanium layer appeared t o make direct contact with the bone and one or a few layers of slender cells were interposed between the bone and titanium. Ultrastructurall y, the titanium came in contact with the bone or the slender cell laye r through a 20 to 40 nm thin amorphous zone. The slender cells at the bone-titanium interface consisted of two types; one was an osteoblast type with glycogen granules which was found along the newly-formed bon e facing titanium layer. The other was a fibroblast type which came in contact with the titanium layer and occasionally endocytosed the deta ched titanium fragments. In addition, some of the slender cells also s howed degenerative changes. Immunocytochemically, cathepsins B and/or D were sometimes colocalized in some phagolysosomes with titanium frag ments. These findings suggested that the fibroblast types at the bone- titanium interface may act as scavengers to remove both cell debris an d titanium by means of some endocytotic ability, and lysosomal catheps ins also developed in response to the endocytosed titanium. The osteob last type also appears to show a high degree of osteogenic activity ar ound the titanium-coated plastic implants.