Rat model of distraction osteogenesis

Prior studies of distraction osteogenesis in dog and rabbit models have shown predominantly intramembranous bone formation. Other models of fracture healing normally display mixtures of both endochondral and intramembranous bone formation. We have established a rat model of tibial lengthening that reliably reproduces the pattern of zonal osteogenesis previously observed in dog and rabbit models. A distraction rate of 0.25 mm twice a day with a 0-day latency period produced intramembranous bone with zones of progressive mineralization from collagen. With this protocol, rats bridged the distraction gap with a 25% increase in the tibial bone length. After 20 days of distraction and 50 days of consolidation, the three-point bending stiffness, as a percentage of the contralateral control, reached a level equivalent to that measured in the canine model for a 15% lengthening (28-day distraction and 84-day consolidation). Radiodensitometric analysis of the regenerate bones measured 97% of the unaffected contralateral tibial densities, and mineral analyses demonstrated that calcium and phosphorus levels in the regenerate bone reached 78% of contralateral tibial levels by day 70. We concluded that a rat model of distraction ostegenesis will be useful for a wide range of studies involving rapid intramembranous bone formation.     

Depressed spontaneous cellular cytotoxicity associated with normal or enhanced antibody-dependent cellular cytotoxicity in patients on chronic haemodialysis.

Lymphocyte function as assessed by spontaneous cellular cytotoxicity (NK) and antibody-dependent cellular cytotoxicity (ADCC) was studied in a group of 23 patients with end-stage renal disease who were being maintained on haemodialysis. The mononuclear cells from 12 (50%) of these patients were markedly reduced in their ability to effect NK activity. When mononuclear cells from 13 patients were examined for ADCC activity, however, only two displayed reduced cytotoxicity. The remainder showed either normal or enhanced ADCC activity against erythrocyte targets. Five patients with consistently low NK cell function demonstrated a significantly enhanced ADCC function when compared with normal controls. Several patients were tested repeatedly over a period of 6 months and we found that these two mononuclear cell functions remained consistent during this time. A reduction in NK activity may reflect a lessened capability for immunosurveillance in these patients.