The Kg‐antigen, RhAG with a Lys164Gln mutation, gives rise to haemolytic disease of the newborn

Abstract

The Kg-antigen was first discovered in an investigation of a mother whose infant had haemolytic disease of the newborn (HDN). The antibody against the Kg-antigen is believed to be responsible for HDN. The Kg-antigen is provisionally registered under the number 700045, according to the Red Cell Immunogenetics and Blood Group Terminology. However, the molecular nature of the Kg-antigen has remained a mystery for over 30 years. In this study, a monoclonal antibody against the Kg-antigen and the recombinant protein were developed that allowed for the immunoprecipitation analysis. Immunoprecipitants from the propositus' red blood cell ghosts were subjected to mass spectrometry analysis, and DNA sequence analysis of the genes was also performed. A candidate for the Kg-antigen was molecularly isolated and confirmed to be a determinant of the Kg-antigen by cell transfection and flow cytometry analyses. The Kg-antigen and the genetic mutation were then screened for in a Japanese population. The molecular nature of the Kg-antigen was shown to be RhAG with a Lys164Gln mutation. Kg phenotyping further clarified that 0Á22 % of the Japanese population studied was positive for the Kg-antigen. These findings provide important information on the Kg-antigen, which has been clinically presumed to give rise to HDN.

Anti‐Kg antibodies induce monocyte phagocytosis of the red blood cells

“…1 We recently detailed the molecular nature of this antigen and clarified that the Kg antigen is an Lys164Gln mutation in the RhAG family (RHAG: ISBT030), using proteomic analysis. 2 In this study, we further elucidated the importance of anti-Kg antibodies in the pathogenesis of HDFN, using the monocyte monolayer assay (MMA). A unique flow cytometry (FCM) phagocytosis assay for MMA has been reported, by using which the phagocytic activity of an antibody can be quantified by counting phagocytized RBCs in the monocytes after co-culture.…”

International Society of Blood Transfusion Working Party on Red Cell Immunogenetics and Blood Group Terminology Report of Basel and three virtual business meetings: Update on blood group systems

“…The molecular nature of the Kg antigen has remained a mystery for over 30 years. A monoclonal antibody to the Kg antigen and recombinant protein were developed that allowed for immunoprecipitation analysis [41]. Immunoprecipitates from the proposita's RBC ghosts were subjected to mass spectrometry analysis.…”

When recombinant proteins can replace rare red cells in immunohematology workups

“…b Kg antibody inhibited by the RhAG protein expressed on the surface of Chinese Hamster Ovary cells. 95 For all new antigens, several lines of evidence are sought and rBGPs are just another, yet readily available, line of evidence. The approach of using rBGPs may have a wider application and would enable more laboratories to participate in the search and definition of new blood group antigens.…”

“…Since 1996, multiple studies have exploited soluble or cell membrane‐bound recombinant proteins to screen human sera for blood‐group‐specific antibodies (Table 1). 27,29,32,44–95 There are 190 red cell antigens classified as high‐prevalence by the ISBT (see web resources) 96 . To identify antibody specificities against all high‐prevalence antigens, up to 190 distinct red cells lacking high‐prevalence antigens or lacking the whole carrier protein would be needed.…”

“… b Kg antibody inhibited by the RhAG protein expressed on the surface of Chinese Hamster Ovary cells 95 …”