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

HLA alloimmunization following blood transfusion results from recipien t exposure to donor alloantigens. Numerous studies have documented tha t intact donor leukocytes are capable of provoking primary alloimmuniz ation and that leukoreduction can decrease the incidence of primary HL A alloimmunization. HLA antigens also exist in soluble form and are pr esent on leukocyte cell fragments. We measured the concentration of so luble HLA class I antigen in both standard and leukoreduced blood comp onents during storage. Although the concentration of soluble class I H LA protein varied widely among different individuals, the concentratio n was stable during refrigerated storage of red cell concentrates and was not affected by leukocyte reduction by filtration. We also investi gated whether or not HLA antigens present on leukocyte fragments were capable of stimulating either resting or in-vitro-primed lymphocytes i n 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 s econdary MLR even in cultures supplemented with recombinant interleuki n-2. These studies provide in vitro evidence to support the hypothesis that HLA antigens are not shed from intact cells to soluble forms dur ing storage and that HLA alloantigens on cell fragments do not elicit a cellular immune response.