HLA DR4 ANTIBODIES CAUSE POSITIVE HTLV-III ANTIBODY ELISA RESULTS

Abstract

Human T-cell lymphotropic virus type III (HTLV-III) can be grown on the leukemic cell line H9 and prepared for HTLV-III antibody testing by enzyme-linked immunosorbent assay (ELISA). 2 kits licensed by the US Food and Drug Administration are now available for screening of blood donors and high-risk groups. We have tested HLA antisera in the Abbott ELISA (batches 74089 HR and 75207 HR). 152 HLA-A B C antisera (commercially available or obtained via exchange programs) were clearly negative. However of 310 HLA-DR antisera 10 gave positive HTLV-III antibody results. The HTLV-III antibody ELISA from Electro-Nucleonics Inc (fistributed by Viramed Munich) master lot 2362 HTLV-III plate lot 4301018 also gave positive results with all of the above HLA-DR4 antisera except for 9w594. These data suggest that DR4 is present on the H9 cell and also as a contaminant on the HTLV-III antigen coated beads used for ELISA test. The fact that no other DR specificity was detected besides DR4 may indicate DR4 homozygosity or heterozygosity for DR4 and an unknown 2nd DR antigen or loss of the 2nd DR antigen on the infected leukemic H9 cell line. Cross-absorption studies with DR4-positive B-cell suspensions revomed the DR4 antibodies from Biotest 512731 and Frsenius 7297 (loss of reactivity against DR4-positive B cells in the 2-color-fluorescence technique); a subsequent HTLV-III test on the absorbed sera became clearly negative. A direct absorption of DR4 antisera on the antigen-coated test beads for further tests of DR4 reactivity was impossible because of the necessary 1:440 predilution of the sera in the standard ELISA procedure. Since an antigenic relation between HLA-DR4 and HTLV-III or the probability that all 9 donors of the different DR4 antisera were HTLV-III infected is unlikely the recognition of DR4 antibodies in the sera of homosexuals (immunized by sperm and white blood cells) hemophiliacs and patients on hemodialysis is important in the interpretation of positive HTLV-III antibody ELISA results. (full text)