Studies on the cellular modulation in cryopreservation focusing the allogenicity of thoracic tissues

背景：深低温保存的同种异体心脏瓣膜和血管已广泛应用于心胸外科。收获的组织通常在程序化的冷冻机中冷冻，这使得能够缓慢冷冻并避免由冰点附近的外来热造成的组织破坏。已经发现冷冻保存的气管比新鲜气管更容易植入。冷冻保存程序似乎降低了同种免疫原性。本研究主要探讨了冷冻保存对气管组织中细胞（气道上皮细胞、血管内皮细胞和成纤维细胞）同种异体性的影响。通过流式细胞术测定用干扰素-γ（IFN）增加同种异体分子表达的程度来评估同种异体活性。结果：程序冻存的细胞在各细胞系中均保持了良好的活力。IFN诱导细胞表面HLA-Ⅱ类分子表达，除气道上皮细胞外，冻存后细胞表面HLA-Ⅱ类分子表达无明显变化。冻存的气道细胞系在表达HLA-II类抗原方面对IFN不太敏感。结论：冻存过程对人气管组织中细胞的同种免疫原性有不同程度的调节作用。冷冻保存是否有利于同种异体移植物的持续时间是有争议的。细胞活力的保持对于同种异体移植物的耐久性是必不可少的，然而，它也与移植物的同种异体性有关。有关抗原呈递细胞的进一步研究，如同种异体移植物中包含的树突状细胞，将揭示冷冻保存组织中同种异体性的调节。

Background : Cryopreserved human allogenic heart valves and vessels have come to be widely utilized in cardiothoracic surgey. The harvested tissues are usually frozen in a programmed freezer, which enables slow freezing and avoids tissue destruction by the exotic fever around the freezing point. Cryopreserved tracheas have been found to be more easily implanted than fresh tracheas. The cryopreservation procedure seems to decrease alloimmunogenicity. In this study focused the influence of cryopreservation on the allogenicity of cells included in the tracheal tissue, i.e. airway epithelial cells, vascular endothelial cells and, fibroblasts.Methods : Viability of the cells was determined by colorimetric MTT assay. Allogenic activity was assessed by flow-cytometric assay determining the degree of increase in expression of allogeneic molecules with interferon-gamma (IFN). One-way mixed lymphocyte-stimulator cell culture (MLC) was also made up.Results : Viability of program-frozen cells was well preserved in each cell line. Expression of HLA-class II on cell surface was evoked by IFN, which ms not deteriorated by cryopreservation except for the airway epithelial cell. The cryopreserved airway cell line was less sensitive to IFN in expressing HLA-class II antigen. MLC of fibroblast and lymphocyte showed no decreased reaction even after the fibroblast was cryopreserved and thawed.Conclusions : Process of cryopreservation variously modulated the allogeneic immunogenicity of the cells included in the human tracheal tissue. It is controversial whether the cryopreservation is favorable for duration of the allograft. Preservation of the cell viability is essential for durability of the allograft, however, it is also associated with the allogenicity of the graft. Further studies concerning the antigen presenting cells, such as the dendritic cells included in the allograft, would reveal the modulation of allogenicity in cryopreserved tissues.