HLA antigens on red cells. Implications for achieving low HLA antigen content in blood transfusions

HLA antigens on red cells were measured using the W6/32 monoclonal antibody as well as with other monoclonal antibodies directed to monomorphic determinants of HLA Class I molecules. Antibody binding was quantitated indirectly by either radioimmunoassay or flow cytometry. Red cells from approximately 50 percent of blood donors bound HLA-A, B, and C antibodies but not antibodies to HLA-DR or those directed to other leukocyte-specific antigens. Persons with HLA-B7-positive lymphocytes consistently expressed measurable red cell HLA antigens. However, 35 percent of donors with HLA-B7-negative lymphocytes also expressed HLA on red cells, and this expression did not correlate with any other HLA antigen. Storage did not affect expression of HLA antigens in red cells stored at 4 degrees C for 21 days or in red cells that had been cryopreserved. Contrary to previous reports, red cells expressing HLA antigens also had beta-2-microglobulin detected, suggesting that the HLA molecules in red cells are similar to those in lymphocytes and other cells, and consequently, that they have the potential to be immunogenic. These results demonstrate that patients requiring multiple transfusions will be exposed to HLA antigens even if they receive blood units depleted of leukocytes and platelets.