The up-regulation of human leukocyte antigens (HLA) class I and class II, has been suspected of involvement in chronic rejections following orthotopic heart transplantations (OHT). A total of forty four endomyocardial biopsy specimens from 11 patients were immunohistochemically analyzed at intervals of 7±2, 30±4, 84±10 and 340±40 days following OHT. The immunohistological study was based on cryostat sections using monoclonal mouse anti-human HLA antibodies. To detect bounding primary antibodies, the DAKO LSAB¨+ Kit/Alkaline Phosphatase detection system was used. For the assessment of the intensity of staining, a semiquantitative scale of 0-3 was employed. HLA class I (ABC) and class II (DR) staining ³2+ was clinically significant. The study group consisted of patients with ischemic cardiomyopathy (six patients) and dilated cardiomyopathy (five patients) as an indication for OHT. The mean donor ischemia time was 116 minutes (ranging between 45 and 194). None of the patients died during the 14 months observation period. Histological rejection(³2) during the time of the immunohistological study was seen in 2 cases at 7±2 days, in 5 cases at 30±4 days, in 3 cases at 84±10 days and in 1 patient at 340±40 days following OHT. In all endomyocardial biopsies, a late expression (300 days post OHT) of HLA-ABC and HLA-DR occurred as moderate (1/11) and severe (10/11). A significant expression of HLA was only seen in one patient at 7± days following OHT, (7±, vs 300±, p=0.005). This expression had a strong diffuse character and was associated with histological signs of an acute injury. Generally, in contrast to focal and vascular staining during the early period, late staining was diffuse in distribution, including sarcolemmic myocyte staining without histologic signs of myocyte injury. In addition, HLA-DR staining was more intense in capillary endothelial cells as opposed to HLA-ABC, which predominated on myocytes. Late up-regulation of HLA in the myocardium may reflect the time-dependent chronic rejection, without histological signs of a myocardial injury. Our results confirm the hypothesis that the microvascular expression of HLA during an acute rejection may differ from that seen in the chronic state.

Keywords: orthotopic heart transplantation, immunohistology, HLA molecules