HLA expression in aortic and pulmonary homografts: effects of cryopreservation.

ABSTRACT

BACKGROUND: The present study was undertaken to find out the HLA allo-antigens on cardiac homografts. METHODS AND RESULTS: One pulmonary and eight aortic homografts were studied for the presence of major HLA class I and class II antigen expression. Cadaveric hearts were procured from the mortuary and kept in Hank's balanced salt solution with antibiotics at 4 degrees C. Bits were taken from the conduits and valves every 24 hours for 14 days during storage and snap-frozen using liquid nitrogen. A total of 1368 sections were made using a cryostat. These sections were stained using 4 monoclonal antibodies BLA class I (MO736), class II HLA-DR (MO746), CD45 (MO701), and endothelial stain (MO616). All monoclonals were procured from DAKO. Class I antigen molecules could be demonstrated on the endothelial surface of the vessel wall from day 1 to day 4 to 5 of storage. They stained weaker and could not be demonstrated after day 10 of storage. Class I antigen molecules were positive in very fresh valves and by day 5-6 could not be seen on the valve surface. Class II (HLA-DR) antigen expression was present in the subendothelial layer from day 1 to day 12-14 of storage. They could also be demonstrated in valves and conduits released after cryopreservation. These class II staining cells were also stained by CD45 monoclonal antibody and hence could be macrophages, histiocytes or leucocytes. The endothelium was very well demonstrated in the vessel walls from day 1 to day 12-14 of storage; it could only be seen in very fresh valves. Storage in the liquid medium and sterilization procedures led to loss of endothelial lining of the valves. After cryopreservation and thawing, class I antigen molecules could not be demonstrated on the valves and conduits. Class II antigen molecules and CD45-stained cells continued to be demonstrated in the subendothelial layer and the valve matrix. The endothelium was intact in the vessel wall after cryopreservation and thawing, but could not be seen in the released valves. CONCLUSIONS: Allograft aortic and pulmonary conduits and valves are immunogenic, and HLA-ABC and HLA-DR antigen molecules can be demonstrated on different components of the vessel wall and valve leafets.