Redefining peripheral tolerance in the BALB/c to CBA mouse cardiac allograft model - Vascular and cytokine analysis after transient CD4 T cell depletion

Background. To evaluate cardiac allografts from recipients that had achieve d peripheral tolerance after transient CD4+ T cell depletion, we analyzed c ellular infiltrate, cytokine expression, and vascular thickening. Long-surv iving cardiac allografts from tolerant recipients were compared with acutel y rejecting allografts and isografts. Methods and Results. In CBA mice treated with anti-CD4 (GK1.5, 0.5 mg intra peritoneally on days 1-28), BALB/c cardiac allografts survived >100 days. T hese recipients were tested for tolerance at >70 days, by challenge with do nor and third-party (C57BL/6) skin grafts. BALB/c skin grafts survived>80 d ays, although C57BL/6 skin was rejected in <12 days, reflecting alloantigen -specific peripheral tolerance. When vascular thickening in gk aft arteries was assessed and computerized measurements performed, heart allografts fro m tolerant recipients showed significantly increased percentage of luminal occlusion compared with isografts (47% compared with 1.2%). Semiquantitativ e reverse transcriptase-polymerase chain reaction was used to assess normal ized intragraft mRNA transcripts for cytokines and T cell markers, with imm unoperoxidase staining of frozen sections to confirmed the presence of prot ein. Compared with rejecting grafts, well-preserved hearts from tolerant mi ce had lower levels of macrophage and T cell infiltration and decreased tra nscription of interferon-gamma, interleukin (IL)-2, IL-10, and inducible ni tric oxide synthase. IL-4 expression was similar in both groups. Conclusions. The degree of tolerance achieved allowed specific acceptance o f donor skin grafts, preserved primary graft function, and reduced inflamma tory activation. Tolerance did not, however, completely prevent macrophage and T cell infiltration of the graft or the development of vascular lesions typical of chronic rejection.