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We have recently demonstrated that one of our monoclonal antibodies (MAB's) to glial fibrillary acidic protein (GFAP) recognizes an epitope on this molecule which is to a large degree blocked during fixation with formaldehyde or crosslinking with Dithiobis (Succinimidyl) Propionate (DTSP). This was shown to be due to the crossbinding of a single or a number of proteins to the GFAP and is not due to a change in the epitope on GFAP induced by the fixation itself. In an attempt to produce further MAB's capable of recognizing epitopes on the GFAP molecule available following formaldehyde fixation, we immunized BALB-C mice with cytoskeletal preparations of human glioma cells which contain GFAP where the blocking protein or proteins were crossbound by DTSP or formaldehyde to the GFAP. Following fusion of the spleen lymphocytes to Sp 2/0 myeloma cells we have cloned hybridomas which produce antibodies that recognize GFAP in formaldehyde fixed tissues. This method presents the antigen in its native "fixed" state for the mouse's immune system and avoids the production of MAB's which (although excellent for immunochemical studies) do not recognize any epitopes available on the molecule in question in formaldehyde fixed tissues. Antibodies so produced are of great interest in routine pathology where most tissues are still, unfortunately, undiscriminately fixed in formalin. The results also show that GFAP varies immunologically in different species (i.e. human v. rat/mouse) and confirm that the GFAP of the PNS is immunologically distinct and/or associated with different proteins from that found in the CNS.

Ten cylindrical implants, made of polycarbonate and covered with a 120-250-nm-thick layer of pure titanium, were implanted into each tibial metaphysis of five rabbits. Observation time was 12 weeks. The implants were surrounded by mature, living bone. No soft tissue intervened between bone and implant at any point. With TEM microscopy the titanium was shown to be bordered by a 20-nm-thick layer of proteoglycans, showing the characteristics of ground substance, and separating the collagen from the implant surface. Cells at the interface were likewise separated from the titanium by such a layer. Hydroxyapatite crystals were observed within the ground substance layer, occasionally seemingly in direct contact with the titanium. Normal mineralization was present 100-500 nm from the implant surface. While this study aims at defining interface anatomy, it also shows that macroscopically smooth-surfaced titanium can readily heal into bone without a soft tissue envelope. This could be of help for materials' choice and design of permanently fixed implants.