DSLK and Kg: Antithetical antigens in the RHAG blood group system, and characterization of anti-DSLK antibody.

BACKGROUND AND OBJECTIVES: The RHAG blood group system contains five antigens: Duclos (RHAG001), Ola (RHAG002), DSLK (RHAG003), Kg (RHAG005) and SHER (RHAG006). Individuals who are DSLK-negative and Kg-positive have the same allele RHAG*01.-3, with a single-nucleotide variation (rs144305805), c.490A>C (p.Lys164Gln), in exon 3 of the RHAG gene. We aimed to confirm whether DSLK and Kg are antithetical antigens. MATERIALS AND METHODS: Blood samples of the original DSLK-negative proband with anti-DSLK, her son and another DSLK-negative individual were examined. The RHAG gene was analysed by polymerase chain reaction and Sanger sequencing. Immunocomplex capture fluorescence assays (ICFAs) and monocyte phagocytosis assays were performed to characterize the anti-DSLK antibody. Cross-testing of alloanti-DSLK and monoclonal anti-Kg (OSK46) was performed using transduced HEK293 cells by inducing the construct of expression vectors encoding wild-type RHAG*01 or the variant RHAG*01.-3. RESULTS: ICFA using monoclonal anti-RHAG (LA18.18) revealed that the anti-DSLK and anti-Kg antibodies reacted with the wild-type and variant RhAG (Rh-associated glycoprotein), respectively. The proband and a DSLK-negative individual appeared to be homozygous for variant RHAG*01.-3, and the proband's son was typed as RHAG*01/RHAG*01.-3 heterozygote. HEK293 cells with wild-type RhAG reacted with the anti-DSLK but not anti-Kg antibody, whereas HEK293 cells expressing the variant RhAG reacted with the anti-Kg but not anti-DSLK antibody. Monocyte phagocytosis assays indicated that 64% of red cells sensitized with anti-DSLK were phagocytosed by monocytes. CONCLUSION: Our results demonstrate that DSLK and Kg are antithetical antigens in the RHAG blood group system. Anti-DSLK may be a clinically significant antibody.