HLA ANTIGENS ON LEUKOCYTE FRAGMENTS AND PLASMA-PROTEINS - PRESTORAGE LEUKOREDUCTION BY FILTRATION

HLA alloimmunization following blood transfusion results from recipient exposure to donor alloantigens. Numerous studies have documented that intact donor leukocytes are capable of provoking primary alloimmunization and that leukoreduction can decrease the incidence of primary HLA alloimmunization. HLA antigens also exist in soluble form and are present on leukocyte cell fragments. We measured the concentration of soluble HLA class I antigen in both standard and leukoreduced blood components during storage. Although the concentration of soluble class I HLA protein varied widely among different individuals, the concentration was stable during refrigerated storage of red cell concentrates and was not affected by leukocyte reduction by filtration. We also investigated whether or not HLA antigens present on leukocyte fragments were capable of stimulating either resting or in-vitro-primed lymphocytes in the mixed lymphocyte reaction (MLR). Leukocyte fragments prepared by repeated freeze-thaw were found to express both class I and class II KLA antigens, but fragments were not able to stimulate in primary or secondary MLR even in cultures supplemented with recombinant interleukin-2. These studies provide in vitro evidence to support the hypothesis that HLA antigens are not shed from intact cells to soluble forms during storage and that HLA alloantigens on cell fragments do not elicit a cellular immune response.