Natural killer (NK) cells are programmed to kill target cells without prior antigen priming. Because of their potent cytolytic activities, NK cells are one of the key cell types involved in dismantling allografts. However, in certain transplant models, NK cells also express potent immunoregulatory properties that promote tolerance induction. The precise mechanism for such striking dichotomy remains unknown. In the present study, we showed in a skin transplant model that the skin allografts contain a subset of antigen-presenting cells (APCs) that can home to the recipient mice. We also showed that such graft-derived APCs are usually destroyed by the host NK cells. But in the absence of NK cells, donor APCs can survive and then migrate to the host lymphoid and extralymphoid sites where they directly stimulate the activation of alloreactive T cells. T cells activated in the absence of NK cells are more resistant to costimulatory blockade treatment, and under such conditions stable skin allograft survival is difficult to achieve. Our study identified a novel role for NK cells in regulating T cell priming in transplant models, and may have important clinical implications in tolerance induction.
Calcaneal fractures are rare injuries in children and adolescents, and fractures with displaced intra-articular fracture patterns are even more rare. The purpose of this study was to report 9 intra-articular calcaneal fractures in 8 children (mean age, 12.6 years; range,10-15 years) treated with open reduction and internal fixation (ORIF) and to examine cases reported in the literature to better define the classification characteristics and operational outcomes of this uncommon fracture. Preoperative radiographs and computed tomography scans were used to evaluate and classify the fractures. Clinical and radiographic examinations were performed at postoperative follow-up, and functional outcome was assessed with the modified American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot score. Mean follow-up was 47 months (range, 21-72 months). Mean time to union was 9.2 weeks (range, 8-12 weeks). Mean modified AOFAS score was 65.2 points (range, 53-68 points). One foot experienced a minor complication.After a systematic review of the literature, 4 studies with a total of 35 patients (37 fractures) were included. All fractures were caused by high-energy injuries. Based on the Essex-Lopresti classification, 40.5% (15/37) were tongue-type fractures and 59.5% (22/37) were joint depression-type fractures. Based on the Sanders classification, 62.2% (23/37) of fractures were 2 parts, 32.4% (12/37) were 3 parts, and 5.4% (2/37) showed comminution. No significant difference was found in classification information between children and adults. The authors concluded that the characteristics of intra-articular calcaneal fractures in children are similar to those in adults, and operative treatment of these fractures yields good results with few complications.
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