Serum antibody reactivity of broadly sensitized patients with HLA-matched peripheral blood T lymphocytes

The sera of 45 hypersensitized patients with more than 90% panel reactive antibodies were tested for reactivity against peripheral blood T lymphocytes from 7 donors matched for HLA-A,B antigens. The target cells were phenotypically homozygous HLA-A1,B8 or A2,B44. Tests for lymphocytotoxic antibodies were essentially negative except for one target cell in which 10 of 25 sera were positive. More positive reactions were detected by flow cytometry, and the proportion of positive specimens ranged from 15% to 48% with the different target cells. Most positive reactions involved the HLA-A2 and B44 antigens, in which heterogeneity within the serologically defined specificities has been described. The positive reactions were further evaluated by testing the effect of purified soluble HLA molecules on the binding of antibodies to the HLA-marched targets. Purified HLA produced a detectable inhibition of antibody binding in the majority of the serum-target combinations studied. These results document that anti-HLA antibodies can still react with HLA-matched lymphocytes, which may be due to the recognition of subtypes of the known serologically defined specificities.