Intrathymic immune modulation prevents acute rejection but not the development of graft arteriosclerosis (chronic rejection)

Background. We showed previously that our intrathymic immune modulation protocol induces virtually permanent graft survival of simultaneously transplanted cardiac allografts in MHC-incompatible rat strain combinations. It is, however, unknown whether this procedure prevents the development of graft arterial disease (GAD).Methods. Male AO recipient rats were intrathymically inoculated with 2.5 x 10(7) PVG splenocytes immediately followed by heterotopic transplantation of a PVG cardiac allograft (day 0). Immunosuppression consisted of 1 mi of antilymphocyte serum i.p. (day 0) and cyclosporine i.m. (15 mg/kg body weight) on days 1, 2, and 3 posttransplantation. Histological analysis, mixed lymphocyte reactions, and intragraft cytokine mRNA expression were performed at several time points after engraftment.Results. Histological analysis revealed that GAD was already present 14 days after transplantation. At 200 days, virtually all vessels were affected and over 80% of the vessels showed severe intimal lesions, Infiltrate analysis displayed massive parenchymatous infiltrates (CD8(+) cells and ED1(+) macrophages) 2 weeks after transplantation. At later time points, infiltrates became epicardial and/or blood vessel associated and mainly consisted of CD4(+), CD8(+), and B cells. Mixed lymphocyte reactions showed nonspecifically decreased responses at 60 days but complete restoration of these responses at later time points (120 to 280 days). Intragraft cytokine mRNA expression showed decreased interleukin-2/interferon-gamma and sustained interleukin-10 expression 2 weeks after transplantation. Transforming growth factor-p mRNA expression was increased >200 days after transplantation.Conclusions. Intrathymic immune modulation does not abolish alloreactivity, and despite induction of long-lasting graft survival, this procedure does not prevent and may even facilitate the development of GAD.