Judith W. Cook

Cytomegalovirus-Mediated Upregulation of Chemokine Expression Correlates with the Acceleration of Chronic Rejection in Rat Heart Transplants

ABSTRACT Cytomegalovirus (CMV) infections have been shown to dramatically affect solid organ transplant graft survival in both human and animal models. Recently, it was demonstrated that rat CMV (RCMV) infection accelerates the development of transplant vascular sclerosis (TVS) in both rat heart and small bowel graft transplants. However, the mechanisms involved in this process are still unclear. In the present study, we determined the kinetics of RCMV-accelerated TVS in a rat heart transplant model. Acute RCMV infection enhances the development of TVS in rat heart allografts, and this process is initiated between 21 and 24 days posttransplantation. The virus is consistently detected in the heart grafts from day 7 until day 35 posttransplantation but is rarely found at the time of graft rejection (day 45 posttransplantation). Grafts from RCMV-infected recipients had upregulation of chemokine expression compared to uninfected controls, and the timing of this increased expression paralleled that of RCMV-accelerated neointimal formation. In addition, graft vessels from RCMV-infected grafts demonstrate the increased infiltration of T cells and macrophages during periods of highest chemokine expression. These results suggest that CMV-induced acceleration of TVS involves the increased graft vascular infiltration of inflammatory cells through enhanced chemokine expression.

Homocysteine and arterial disease: Experimental mechanisms

Hyperhomocysteinemia (hH(e)) in the general population is associated with incidence and progression of arterial occlusive disease, although the underlying mechanisms are not well defined. Current research supports a role for homocysteine (H(e))-mediated endothelial damage and endothelial dysfunction. This mechanism appears to be a key factor in subsequent impaired endothelial-dependent vasoreactivity and decreased endothelium thromboresistance. These consequences may predispose hyperhomocysteinemic vessels to the development of increased atherogenesis. Additional mechanisms of H(e)-mediated vascular pathology, including protein homocysteinylation and vascular smooth muscle cell proliferation may also play a role. Continued investigation into the mechanisms contributing to H(e) toxicity will provide further insight into the processes by which hH(e) may increase atherosclerosis.

Elimination of donor-specific alloreactivity prevents cytomegalovirus-accelerated chronic rejection in rat small bowel and heart transplants

BACKGROUND The primary cause for late failure of vascularized allografts is chronic rejection (CR) characterized by transplant vascular sclerosis (TVS). Cytomegalovirus (CMV) infection accelerates TVS and CR by unclear mechanisms involving direct effects of CMV, indirect effects of the recipients immune response to CMV, or interactions between CMV and the recipients alloreactivity. This study examined the role of CMV and the alloreactive response in the development of TVS using bone marrow chimerism (BMC) in rat small bowel (SB) and heart transplantation models. METHODS Fisher 344 (F344) rat heart or SB grafts were transplanted into F344/Lewis bone marrow chimera. F344 heart or SB grafts transplanted into Lewis recipients (low-dose cyclosporine) were positive controls for the development of TVS. Lewis heart or SB grafts transplanted into Lewis recipients (+/-cyclosporine) were transplantation controls. The effect of rat CMV (RCMV) (5x105 plaque-forming units) on TVS (neointimal index, NI) and graft survival was studied in these groups. RCMV infection was assessed by serologic analysis and quantitative polymerase chain reaction techniques (TaqMan). RESULTS RCMV infection accelerated the time to graft CR (SB 70-38 days; hearts 90-45 days) and increased the severity of TVS in both the SB allografts (day 38, NI=27 vs. 52) and the heart allografts (day 45, NI=43 vs. 83). Grafts from CMV-infected syngeneic recipients failed to develop TVS and CR. Donor-specific tolerance induced by BMC prevented allograft TVS and CR in both transplant models. In contrast to naïve Lewis recipients, RMCV infection failed to cause allograft TVS and CR in bone marrow (BM) chimeras. CONCLUSIONS The events in CMV-induced acceleration of TVS involve a crucial interplay between CMV infection and the recipients alloreactive immune response.

Hyperhomocyst(e)inemia Induces Accelerated Transplant Vascular Sclerosis in Syngeneic and Allogeneic Rat Cardiac Transplants

Chronic rejection (CR) and transplant vascular sclerosis (TVS) cause the majority of graft failures in cardiac transplantation. Hyperhomocyst(e)inemia [hH(e)] is associated with human TVS without a proven causal relationship. This study investigated the effect of hH(e) on graft survival and TVS in allogeneic and syngeneic rat cardiac transplants. Lewis recipients of heterotopic F344 heart allografts, received normal or hH(e)‐inducing (↓folate, ↑methionine) diets {controls: syngeneic transplanted [± hH(e), + CsA] and nontransplanted rats [± hH(e), ± CsA]}. Serial plasma homocyst(e)ine [H(e)] levels were measured. TVS was assessed in clinically rejected grafts and a subset of pre‐rejection normal diet allografts (day 64) (neointimal index, NI). The hH(e) diet elevated plasma H(e) levels. When compared with normal diet controls (n = 9), hH(e) diet allografts (n = 9) had decreased time to onset of CR (40 ± 9 vs. 72 ± 10 d, p = 0.02), and graft failure (64 ± 10 vs. 107 ± 12 d, p = 0.009). hH(e) diet allografts at rejection (n = 9, 64 d) had more severe TVS (NI = 68 ± 2) than both time‐matched normal diet allografts (NI = 49 ± 6, n = 8, 64 d, p < 0.001) and normal diet allografts at rejection (NI = 58 ± 5, n = 9, 107 d, p = 0.007). hH(e) induced TVS in syngeneic grafts (NI = 50 ± 3, n = 10 vs. NI = 5 ± 3, n = 10, 130 d, p < 0.001). hH(e) accelerated rejection and increased the severity of TVS in allogeneic cardiac transplants, and induced TVS in syngeneic cardiac transplants.