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17 Once again, CD8+ T cell-depleted animals had a significant reduction in medial SMC apoptosis and significantly higher numbers of medial SMCs when compared to wild-type animals

17 Once again, CD8+ T cell-depleted animals had a significant reduction in medial SMC apoptosis and significantly higher numbers of medial SMCs when compared to wild-type animals. significantly lowered CD8+ T cell counts in peripheral blood, reduced medial SMC apoptosis at 20 days, and increased medial Avibactam sodium SMC counts at 60 days. Both short- and long-allogeneic exposure groups confirmed these findings and exhibited that medial SMC loss is usually proportional to the length of allogeneic exposure. Antibody depletion of CD8+ T cells results in reduced medial SMC apoptosis and better medial SMC preservation. This supports the hypothesis that medial SMC loss occurs by apoptotic death and is driven by CD8+ T lymphocytes. Orthotopic heart transplantation is usually a well-established treatment modality for end-stage heart disease. Immunosuppressive drugs have dramatically improved 1-12 months graft survival. However, loss of organ allografts because of chronic rejection remains a major clinical problem and has become a major limiting factor for long-term survival. It is a leading cause of late graft failure, responsible for 23% to 36% of deaths among patients that survive 1 year after heart transplantation. 1,2 Chronic rejection is usually characterized by a diffuse, concentric intimal proliferative response within the arteries of transplanted organs, termed allograft arteriosclerosis (AAS). 3-5 The presence of AAS can be exhibited in up to 50% of patients 5 years after heart transplantation. 6,7 There is no current therapy for AAS other than retransplantation which has been shown to have much poorer results than the initial transplant in addition to compounding the problem of donor shortage. 8 Avibactam sodium The pathogenic mechanisms of AAS remains primarily unknown. To date, chronic rejection research has focused on allorecognition of graft endothelium with subsequent leukocyte infiltration and production of cytokines, chemokines, and growth factors. 9 In response, vascular clean muscle cells (SMCs) are thought to transmigrate to the intimal compartment resulting in occlusive lesion formation. 10 We, as well as others, have observed that in arteries from both humans and animals undergoing chronic rejection the media undergoes striking thinning and loss of SMCs. 11-14 In an aortic interposition graft model, which is a well-described and reproducible model of AAS, 13,15 medial SMC loss occurred only in allografts. 16 In addition the degree of Avibactam sodium medial SMC loss and intimal proliferation observed were directly proportional to the duration of allogeneic exposure, 17,18 suggesting that medial SMC cell destruction occurs by allo-immune mechanisms and may be linked to AAS. It is also consistent with observations made in arterial injury models, that strong intimal proliferation is dependent on, and proportional to, the extent of medial SMC injury. 19 In this context, we have recently provided evidence that medial SMC loss in allografted arteries occurs by apoptotic cell death and that CD8+ T cell-derived inducers of apoptosis are up-regulated concomitantly. 12 These include granzyme B, perforin, and Fas ligand, Avibactam sodium which are the primary mediators by which cytotoxic T lymphocytes kill target cells. We therefore hypothesized that medial SMC loss occurs by CD8+ T lymphocyte-induced SMC apoptosis rather than migration. We further hypothesize that medial SMC destruction may be linked to myointimal lesion formation. In support of this hypothesis is usually evidence that this proliferating intimal lesion is usually of CCR5 recipient not donor origin (Johnson P, unpublished observations). 20 In the current study we have established a role for CD8+ T lymphocytes in medial SMC loss and evaluated the correlation between this and intimal proliferation in a rat aortic interposition graft model of AAS. To achieve this, CD8+ T lymphocytes were depleted from recipient animals with a depleting mAb to the CD8 molecule (MRC OX-8). We have also used retransplantation experiments that are known to have reduced medial SMC damage and less intimal proliferation 17,18 to explore the impact Avibactam sodium of CD8 depletion around the timing and reversibility of AAS. Materials and Methods Animals Inbred male Brown Norway (RT1.An) and Lewis (RT1.Al) rats weighing 250 to 350 g were purchased from Harlan Sprague-Dawley (Indianapolis, IN) and housed in the Medical Sciences animal care facility. All animals were housed and fed at.