To determine the pattern of cellular expression of donor MHC class I and class II antigens during the course of rat cardiac allograft rejection, ACI cardiac allografts transplanted to BN recipients were examined from day 2 to day 6 using immunohistologic and immunoelectron microscopic methods. We used both monomorphic and donor-specific mouse anti-rat MHC class I and class II mAbs in this study. In normal ACI hearts, MHC class I reactivity was confined to the vascular endothelium and to interstitial cells. Ongoing rejection was characterized by an increased donor MHC class I staining intensity of microvascular endothelium and induction of donor class I surface reactivity on cardiac myofibers. Donor MHC class II reactivity was exclusively confined to interstitial dendritic cells (IDC) in both normal ACI hearts and in rejecting allografts, although rejection was associated with marked fluctuations in class II IDC frequency. An early numerical depression in class II IDC present in both allografts and syngeneic heart grafts was attributed to a direct effect of the transplantation procedure. By days 3-4, allografts showed an absolute overall increase in donor class II IDC frequency, which was associated with the presence of multiple localized high-density IDC-lymphocyte aggregates. The lymphocytes present in the focal areas were predominantly of the class II-reactive Th cell subpopulation. These aggregates may thus represent the in vivo homologue of dendritic cell-lymphocyte clustering, which has been shown to be required for primary class II allosensitization in the rat and mouse in vitro. During the late phase of rejection, there was a marked numerical fall in donor class II IDC, which correlated with extensive overall graft destruction. This study has shown that acute rat cardiac allograft rejection can occur in the absence of donor MHC class II expression by allograft vascular endothelium and cardiac myofibers. The IDC, which are believed to represent the principal class II alloantigen presenting cells in the rat heart, remain the sole class II-expressing cellular constituents of the graft throughout the course of rejection.

No abstract

Endothelins (ET) are potent vasoconstrictors that are directly mitogenic for vascular smooth muscle cells and fibroblasts. It is possible that the vasoconstrictor and mitogenic effects of ET could play a significant role in the vascular remodeling process that occurs in chronic vascular rejection (CVR). We have previously shown that cardiac allografts in the indefinitely surviving major histocompatibility complex identical WF.1L (RT1(1)) to Lewis (LEW) (RT1(1)) inbred rat strain combination provide a highly reproducible model of progressive CVR. The objective of this investigation was to measure endothelin-1 ventricular content of WF.1L-LEW cardiac allografts and to determine the immunohistochemical patterns of ET cellular reactivity at well defined posttransplant time periods. Data were compared with those obtained in similar studies of LEW-LEW syngeneic: heart grafts as well as all recipients' own hearts. The ventricular ET-1 content of the WF.1L cardiac allografts was markedly higher (4.3-, 7.0-, and 4.8-fold at 20, 40, and 60 days, respectively) than in corresponding recipients' hearts. Also, the increase in ventricular ET-1 levels as compared with the recipients' hearts rose significantly only in the allograft group. No comparable differences were observed in the syngeneic heart graft controls. Allografts consistently showed ET staining of intimal myocytes at sites of occlusive and subocclusive intimal proliferation associated with CVR. Allografts also showed ET cellular staining in areas of reparative fibrosis associated with indolent interstitial rejection and ischemic myocardial damage. The results of this study strongly suggest that ET may play a significant role in the pathogenesis of CVR.

No abstract

A p-nitrophenyl alpha-galactoside hydrolase is partially released when whole cells of Pseudomonas atlantica are converted to spheroplasts. The p-nitrophenyl alpha-glactoside hydrolase is completely inactivated by treatment of whole cells with diazonaphthalene -- disulfonic acid (NDS), a reagent which does not penetrate the cytoplasmic membrane. Under the conditions used no inactivation of lactic acid dehydrogenase was observed. A specific staining procedure for this enzyme for use in electron microscopy was developed. The results with this technique in conjunction with the results of spheroplasting and NDS localization suggest that p-nitrophenyl alpha-galactoside hydrolase is located in or on the double-track membranes, primarily on the outer double track.