HLA antibodies as a cause of false‐positive reactions in screening enzyme immunoassays for antibodies to human T‐lymphotropic virus Type III

15,680 volunteer blood donors were screened by enzyme-linked immunosorbent assay (EIA) for antibodies to human T-lymphotropic virus Type III (HTLV-III). On at least two of three determinations, 0.37 percent were found to be reactive. When the first 38 of these samples were sent for repeat EIA and Western blot, the EIA was positive in 14. In only three of these 14 samples was the EIA result confirmed by Western blot. Eight of these eleven false-positive samples were from women who were found to have HLA antibodies. In seven of these women, the HLA antibodies were directed to Class II antigens expressed on the cell used to grow HTLV-III in the preparation of screening EIA kits. We conclude that HLA antibodies are an important cause of false-positive reactions in the screening test for HTLV-III antibody.