International Cell Exchange, 1991.

1. During 1991, lymphocytes from 40 individuals of various races and 20 cultured B-cell lines were sent to 290 laboratories (listed in appendix) for typing. The results of the blind tests were analyzed and reported monthly. This is a summary of the year's 10 monthly exchanges. 2. Ten A-locus antigens showed 95% or greater agreement among laboratories, and 100% agreement was achieved for A2 and A3. Agreement of 95% or more was reached for 7 B-locus specificities. Both Bw54 and Bw73 showed marked improvement in detection during the last 3 years. 3. Six laboratories did not miss the assignment of any A- or B-locus antigens. The false-positive and false-negative assignment rates are given for the A- and B-loci. 4. The following variants were studied: B5-53 variants from various races, BN21, B7x40 (DT), and B7x27. 5. Aw66 assignment was found to be discrepant between the United States and European laboratories. 6. The A28 splits, Aw68 and Aw69, were studied, as were cells with different Aw68 splits. 7. Cell lines were typed by 150 laboratories, including 19 DNA laboratories. Six Class II antigens had 95% or higher detection levels, and 5 others had higher than 90% detection levels. 8. Both DNA and serology laboratories had difficulty in assigning the DRw6 splits, DRw13 and DRw14. The definition of the splits of DR3, DQw1, and DQw3 was clarified with the additional DNA typing results. 9. Amino acid sequencing confirmed a new variant of Bw53, as indicated by the assignments based on serology.