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The detection of virus in osteoclasts from Pagetic patients is now well known, but it has yet to be shown convincingly that the presence of virus in Pagetic osteoclasts influences their behaviour. In this study, osteoclasts from embryonic chick tibiae were infected with canine distemper virus or measles virus and compared with mock-infected controls. Infection was confirmed using virus-specific fluorescent antibodies. It was found that virus infection did not alter osteoclast morphology or tartrate-resistant acid phosphatase (TRAP) activity. Both infected and mock-infected osteoclasts produced resorption pits on bovine bone slices; these could be divided into two distinct size classes with a computer-based measuring system. Virus infection significantly increased the proportion of the larger size class of resorption pit. These results suggest that virus infection can increase bone resorption by osteoclasts, lending further support to the hypothesis that viruses play a role in Paget's disease of bone.

Rodent Achilles tendons were subjected to midpoint tenotomy and allowed to recover for various times in situ before the operated tissue was removed, placed into a Millipore diffusion chamber, and inserted intraperitoneally into syngeneic hosts. Diffusion chambers were then removed at weekly intervals, such that the total time after the operation (i.e., time allowed to recover in situ plus time within the diffusion chamber) was up to 8 weeks, and examined histologically. Ectopic cartilage was produced within the diffusion chamber after a total of 4 weeks but only if the first 2 weeks of recovery were in situ. With increasing time, calcified cartilage, osteoid, and bone were also observed. Overall, the evidence suggests that the cartilage forms via a direct conversion from tendon tissue and that the bone may form as a result of differentiative changes of hypertrophic chondrocytes.

The subcutaneous injection of solutions of chloride salts of the rare earths is followed by calcification of the dorsal fascia in the mouse. The concentration of salt required to produce a constant, predictable response varies from salt to salt. The macroscopic outline of the reaction is generally irregular and therefore a quantitative radiological method has been developed to allow an accurate assessment of the dose/response relationship. This with the majority of salts is best described as a log regression and with three as a linear regression.

The subcutaneous injection of small quantities of LaCl3 and CeCl3 was followed by calcification of the dorsal fascia in mice. The calcification reaction was shown by separate positive histochemical tests for calcium ions (the chloranilic acid reaction) and phosphate (the von Kossa reaction). The injection of cadmium chloride and stannous salts caused damage to and a positive von Kossa reaction in the fibres of the panniculus carnosus muscle. The significance and specificity of the histochemical tests was determined by X-ray microprobe analysis of tissues injected with the above salts and other salts known to cause either combined chloranilic acid and von Kossa positive reactions or isolated von Kossa positive reactions in mouse skin. The pathogenesis of the reactions produced by LaCl3, CeCl3 and KMnO4 was studied by applying histochemical tests to tissues recovered at timed intervals after injection. The reactions produced by LaCl3 and CeCl3 were similar and occurred in the dorsal fascia with positive VK reactions occurring first after 18 followed by positive CA reactions after 24 hr. The distribution of these reactions suggested a haematogenous origin for the constituent ions. The injection of KMnO4 in a much higher dose caused damage to the skin and particularly the fibres of the panniculus carnosus muscle. In contrast to the other salts, the calcific reaction occurred in association with these fibres, showing equally positive von Kossa and chloranilic acid reactions from the early stages.

Systemic treatment with disodium ethane-hydroxy-1,1-diphosphonate is ineffective in inhibiting the calcergenic reactions induced in mouse skin by the lanthanides. In contrast, disodium dichloromethylene diphosphonate prevents lanthanide calcergy induced by 12 of the 15 compounds tested but only when treatment with Cl2MDP is given prior to the subcutaneous (sc) injection of the lanthanide. This is the first experimental calcification system in which EHDP was ineffective in inhibiting the calcification and the first in which Cl2MDP was found to be effective in this regard. It is increasingly apparent that individual members of the diphosphonates show variable anti-calcific effects, that the activity of one particular compound may vary from one test system to another and that the time of application of treatment of the compounds in respect to the application of the initiating stimulus to calcification may be an important factor in determining the efficacy of a particular compound.

Calciphylaxis is a local tissue calcific reaction at the site of an injection of challenger substance given a critical time period after the oral administration of a sensitizer substance such as dihydrotachysterol (DHT), vitamin D or parathormone. Cutaneous calciphylaxis is readily induced in the rat but not in the mouse and this may be because, in the latter, the challenger substance is absorbed rapidly by macrophages. In the rat the administration of 500 micrograms/0.1 ml of DHT followed after 24 h by the subcutaneous (SC) injection of ferric chloride (FeCl3) (30 micrograms/0.1 ml) is followed rapidly by calcification of the SC site. There is an early transient acute inflammatory reaction with the incrustation of collagen fibres by the iron salt and an apparent exudation of calcium and phosphate ions from the bloodstream. These ions also become associated with collagen fibres. Two days after injection macrophages and multinucleated giant cells become the dominant cells. Calciphylaxis is a useful experimental model of ectopic calcification and is associated with an initial hypercalcaemia. The diphosphonates ethane-1-hydroxy-1, 1-diphosphonate (EHDP) and dichloromethylene diphosphonate (Cl2MDP) are effective inhibitors of the calciphylactic reaction when administered prior to the initiation of the experimental procedure.

The subcutaneous injection of mast cell degranulators in the mouse is followed by calcification of fibres of the Panniculus Carnosus muscle. This reaction is seen in damaged fibres adjacent to a central zone of complete necrosis. Calcification of muscle fibres is also seen after the injection of KMnO4 but this uniformly affects the fibres at the site of reaction. Quantitative studies of the latter model and qualitative studies of the former show that treatments with the diphosphonates EHDP and Cl2MDP do not influence the calcific responses. It is suggested that the inducing chemicals interact with the muscle fibre membrane causing membrane dysfunction and a resultant influx of calcium ions. It has been proposed that this is a pathogenetic mechanism in various myopathies and that prevention of net calcium ion influx might form a basis for treatment. In this context, the results of the present experiments suggest that the diphosphonates would be unlikely to efficacious in this regard.

Bone tissue from a patient with chronic renal failure and a dialysis encephalopathy syndrome has been studied by histological and histochemical means, by flame emission spectroscopy and by electron probe X-ray microanalysis. There was significant renal osteodystrophy manifest as an osteomalacia. Emission spectroscopy showed the presence of iron (Fe), aluminium (Al), silicon (Si), zinc (Zn), strontium (Sr), lead (Pb) and copper (Cu) in the concentration range 100-1000 parts per million (ppm). Electron probe X-ray microanalysis showed focal concentrations of Fe and Si in the marrow tissue only, whereas Al was localized to the calcification front zones at the junction of osteoid and mineralized tissue of both trabecular and cortical bone. It is concluded that the presence of Al at these sites could interfere with the mineralization process and significantly contribute to the pathogenesis of haemodialysis-related osteomalacia and that it is unlikely that the other elements detected are significant in this regard.

Local calcergy is an ectopic calcification reaction (due to hydroxyapatite formation) induced in connective tissue sites by the application of dilute solutions of certain metallic salts (calcergens). The phenomenon is usually produced in the subcutaneous tissues of the experimental animal. The single intra-articular injection of lead acetate (PbAc) solution (a known calcergen) into the knee joint of the rat is followed by opacity of the synovial membrane and para-articular tissues with the aggregation of macrophages and multinucleated giant cells and the formation of some granulation tissue. This lesion ultimately resolves and there is no cartilaginous degeneration. Repeated intra-articular injections of PbAc produce pronounced changes in the synovium and para-articular tissues. There is extensive calcific deposition with exuberant macrophage and giant cell accumulation and fibroblastic proliferation. The proliferated synovial membrance becomes adherent to articular cartilage. There is thinning and fragmentation of the latter with focal loss and replacement by fibrous tissue. Therefore, in contrast to the effects of a single injection, repeated calcergenic stimulation of the knee joint is associated with a destructive arthropathy.

The intrarenal injection of Boivin antigen is followed by the development of true melakoplakic lesions as characterised by the accumulation of macrophages containing MG bodies. Similarly the injection of diluted antigen is followed by the accumulation of macrophages with a granular PAS-positive cytoplasm but lacking MG bodies. These experimental models are compared with typical human renal malakoplakia and that entity known as megalocytic interstitial nephritis.

Midpoint tenotomy of the mouse Achilles tendon is followed by regeneration with heterotopic ossification at the junction of tendon stump and the regenerated segment. This heterotopic bone formation occurs through a process of endochondral ossification and the cartilage cells appear to arise by a process of fibroblast transformation. Five weeks after tenotomy 60 per cent. of specimens show cartilage and bone formation whilst the remaining 40 per cent. show chondrification only. After 10 weeks all specimens showed bone formation with trabecular bone and haemopoietic marrow. The treatment of tenotomised animals with either disodium ethane-1, 1-diphosphonate (EHDP) or disodium dichloromethylene diphosphonate (Cl2MDP) has no effect on the process of heterotopic ossification which can be detected at the radiological or light microscopical level.

The reactions to a number of histochemical stains by Michaelis-Gutmann (MG) bodies in 13 cases of malakoplakia are described. All MG bodies contained calcium and phosphate. Iron was present in six cases. Special stains failed to reveal the presence of micro-organisms. In six cases the MG bodies contained either lecithin or sphingomyelin and in three both phospholipids were present. There was no evidence of phospholipid of bacterial cell membrane derivation. Carbohydrate staining reactions suggested the presence of a neutral polysaccharide and an acidic non-sulphated polysaccharide (such as a sialoglycan). No histochemical evidence could be adduced to implicate bacterial cell membranes in the structure of the organic matrix of the MG body. The implications of these findings in the light of the association between clinical bacterial infection and malakoplakia are discussed.

Both disodium pyrophosphate and disodium ethane-hydroxy-1, 1-diphosphate inhibit the reaction of simple calcergy induced in the mouse by lead acetate. The pyrophosphate is effective only by a direct interaction with the lead salt and the disphosphonate is effective only before the occurrence of histochemically demonstrable calcification.

The diphosphonate compound ethane-hydroxy-1, 1-diphosphonate (EHDP) is an effective inhibitor of the calcification reaction induced by the subcutaneous injection of lead acetate in the mouse. Dichloromethylene diphosphonate (CL2MDP) has no such effect and prednisolone and sodium aurothiomalate are also ineffective in inhibiting the reaction. The rate of resorption of the calcified plaque is decreased by C12MDP when this is administered on an extended basis. This effect disappears after prolonged treatment so that EHDP, calcitonin and C12MDP have no effect after 7 weeks of daily treatment.

The ultrastructural features of a case of disseminated malakoplakia are described and compared with available published cases. Generally macrophages were involved (although characteristic inclusions were seen in association with some plasma cells) and contained three types of cellular inclusions. These were (1) the phagolysosomes (2) and intermediate structure sharing features of the phagolysosome and the Michaelis-Gutmann (MG) body and (3) the MG body. All inclusions were delineated by unit membranes and their matrices (except those of large MG bodies) composed of membranous whorls and loops. It is suggested that these inclusions represent stages in the development of the MG body. Septate junctional complexes were observed between phagolysosomes and small MG bodies. These complexes may represent either a mechanism of organelle fusion or an abnormality of molecular organisation of the limiting unit membrane.

The case is presented of an intraspinal meningioma in a 14-yr-old female. After surgical exploration pulmonary metastases became apparent. At necropsy the tumour had increased proportions of the cathodal isoenzymes LDH-4 and 5. This pattern has previously been observed in malignant meningiomas and may be used at the time of biopsy to assess malignancy.