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Cardiovascular
Research Laboratory, Department of Pathology and Laboratory Medicine, St.
Paul's Hospital-University of British Columbia, and Vancouver Vascular Biology
Research Centre, Vancouver, British Columbia, Canada |
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SUMMARY: Apoptosis is associated
with acute rejection, transplant vascular disease, and the "Quilty effect"
in cardiac allografts. However, the causality and mechanisms of apoptosis
in the pathogenesis of vascular injury are poorly understood. In the current
study, the Lewis-to-F344 rat cardiac allograft model was utilized as a means
to immunohistochemically evaluate the expression of Bax, Bcl-2, and factor
VIII-related antigen in transplant vascular disease. Apoptosis was detected
by in situ labeling of fragmented DNA using in situ terminal deoxyribonucleotidyl
transferase-mediated dUTP nick end labeling (TUNEL) in native hearts and
grafted hearts of allogeneic and syngeneic recipients. Bax immunostaining
was detected in 50% of endothelial cells, in 60% of infiltrating
leukocytes associated with acute rejection in the myocardium, and in certain
other parenchymal cells, considering all cardiac allografts. More than 75%
of infiltrating leukocytes in the intima of vessel walls immunostained positive
for Bax. Bcl-2 immunopositivity was not detected in native hearts, allo
allo-, or syngrafts. On Days 2, 4, 7, and 14 after transplantation, TUNEL
positivity was detected in only about 1% of leukocytes in the interstitial
infiltrates, despite the fact that rather severe rejection was observed
in Day 14 allografts. The number of apoptotic leukocytes increased significantly
by Days 28 and 56 after transplantation, although the severity of histopathological
rejection did not increase as compared with Day 14. The apoptotic leukocytes
remained isolated or in small clusters, mainly perivascular. TUNEL positivity
colocalized with Bax expression in these cells. TUNEL staining was also
observed in certain parenchymal cells in the interstitium and in randomly
distributed inflammatory cells in vessel walls. TUNEL positivity was detected
in rare luminal endothelial cells in transverse sections of vessel walls
(about 10% of cells in <1/10 of the vessels studied). Nuclear TUNEL
positivity was observed in Bax-negative cardiomyocytes in ischemically damaged
areas of myocardium in both allografts and syngrafts. In summary, increased
expression of Bax was observed in rat cardiac allografts. The colocalization
of TUNEL and Bax suggests that endothelial cell injury and infiltrating
leukocyte apoptosis may be regulated in part by the apoptosis-promoting
protein, Bax. In the current model, myocyte death due to ischemia and surgical
injury in syngrafts and allografts does not seem to involve Bax. |
