Presence of the DRB4*0103102N null allele in different DRB1*04-positive individuals.

The DRB4 gene encoding the DR53 antigen is present in DRB1*04-, DRB1*07- and DRB1*09-positive individuals. Eight allelic variants of DRB4 have been recognized, 5 resulting in an expressed DR53 antigen and 3 belonging to the null alleles. So far the DRB4*0103102N null allele had been found exclusively in individuals carrying the haplotype DR7,-DQ9. High-resolution typing of HLA class II by polymerase chain reaction using sequence-specific primers (PCR-SSP) and/or sequence-based typing of kidney patients and their families revealed the presence of the DRB4*0103102N null allele segregating with DRB1*04 and DQB1*03 in 4 different families. Three different haplotypes on which the null allele was located, were recognized by family studies: DRB1*0401, DQB1*0301; DRB1*0402, DQB1*0302 and DRB1*0404, DQB1*0302. Determination of the DR53 specificity of antisera reacting with DR53-positive individuals has always been difficult due to the simultaneous presence of DR4, 7 or 9. Identification of DR4-positive DR53-negative individuals as described here, provided the serological reactions with DR53-antisera and revealed the antibody specificities in the antisera used.