Dombrock blood group (DO): assignment to chromosome 12p

Emily Cooley lecture 2012: Emily Cooley and techniques that have been applied to characterize DO and JR blood groups

Emily Cooley was a well-respected medical technologist and morphologist with a remarkable skill set. She was highly regarded both professionally and personally. The "Emily Cooley Lectureship and Award" was established to honor her in particular and medical technologists in general. This article first reviews the history of the Emily Cooley award and provides some of the reasons why it carries her name. Then, using two blood group systems, DO and JR, it illustrates how many discoveries regarding blood groups were dependent on access to techniques.

Complexities of the Dombrock blood group system revealed

The Do(a) antigen was discovered after I began my career in immunohematology and I have been fortunate to be involved in several fascinating discoveries in the Dombrock blood group system. The Do(a) antigen and its antithetical antigen, Do(b), have a prevalence that makes them useful as genetic markers. The paucity of reliable anti-Do(a) and anti-Do(b) has prevented this potential from being realized; however, our ability to type for DO alleles at the DNA level has made it possible to test cohorts from different populations. In 1992, the Dombrock blood group system was expanded to include three phenotypically related antigens, Gy(a), Hy, and Jo(a), when it was discovered that the Gy(a-) phenotype was the null of the Dombrock system. Based on the knowledge that the Dombrock glycoprotein is attached to the RBC membrane via a glycosylphosphatidylinositol linkage and subsequent to the assignment of the corresponding gene to the short arm of chromosome 12, expressed sequence tags from terminally differentiating human erythroid cells were analyzed in silico to identify the DO gene. This allowed determination of the molecular basis of the various Do phenotypes and the realization that DO is identical to the gene encoding a mono-ADP-ribosyltransferase, ART4. No enzymatic activity in RBCs has been demonstrated and the function of this glycoprotein, on the outside surface of RBCs, has yet to be determined. This review is a synthesis of our current knowledge of the Dombrock blood group system.

A panel of monoclonal antibodies recognizing GPI-anchored ADP-ribosyltransferase ART4, the carrier of the Dombrock blood group antigens

ART4 (CD297) is a member of the family of toxin-related ADP-ribosyltransferases (ARTs) and is the carrier of the Dombrock blood group alloantigens (Do). Two mouse monoclonal antibodies (MIMA-52 and MIMA-53), and two rat monoclonal antibodies (N0NI-B4 and NONI-B63) were obtained following immunization of mice with human Do/ART4-transfected cells and of rats with human Do/ART4 cDNA, respectively. All four mAbs recognize Do/ART4-transfected Jurkat cells but not untransfected cells by FACS analysis. Staining of Do/ART4-transfected cells by these mAbs was reduced following treatment of cells with PI-PLC, confirming that Do/ART4 is anchored in the cell membrane by linkage to glycosylphosphatidylinositol as predicted from its amino acid sequence. The four mAbs did not react with Gy(a-) (Dombrock null) erythrocytes but agglutinated other red blood cells. By flow cytometric analysis, all mAbs reacted prominently with erythrocytes, and weakly with peripheral blood monocytes and splenic macrophages, but not with B-lymphocytes or T-lymphocytes. The mAbs reacted weakly also with human umbilical vein endothelial cells and the basophilic leukemia KU-812. Immunohistology revealed staining of epithelia and endothelia on sections of tonsils. In FACS analyses NONI-B4 competed with MIMA-52 for binding to Do/ART4-transfected cells and erythrocytes, whereas NONI-B63 competed with MIMA-53. Neither of the mAbs reacted with mouse ART4-transfected cells, but NONI-B63 and MIMA-53 did react with a mouse/human ART4 chimera, indicating that the epitope recognized by these mAbs lies in the C-terminal half of the protein.

Identification of the Dombrock blood group glycoprotein as a polymorphic member of the ADP-ribosyltransferase gene family

Identification of the 25 known human blood group molecules is of fundamental importance for the fields of erythroid cell biology and transfusion medicine. Here we provide the first molecular description of the “Dombrock” blood group system. A candidate gene was identified by in silico analyses of approximately 5000 expressed sequence tags (ESTs) from terminally differentiating human erythroid cells. Transfection experiments demonstrated specific binding of anti-Dombrock and confirmed glycosylphosphatidylinositol membrane attachment. Dombrock expression is developmentally regulated during erythroid differentiation and occurs at highest levels in the fetal liver. Homology studies suggest that the Dombrock molecule is a member of the adenosine 5′-diphosphate (ADP)–ribosyltransferase ectoenzyme gene family. Genotypic comparisons suggest Doa versus Dob antigenicity results from a single amino acid substitution within an encoded arginine-glycine-aspartic acid (RGD) motif of the molecule.

Identification of the Dombrock blood group glycoprotein as a polymorphic member of the ADP-ribosyltransferase gene family

Identification of the 25 known human blood group molecules is of fundamental importance for the fields of erythroid cell biology and transfusion medicine. Here we provide the first molecular description of the “Dombrock” blood group system. A candidate gene was identified by in silico analyses of approximately 5000 expressed sequence tags (ESTs) from terminally differentiating human erythroid cells. Transfection experiments demonstrated specific binding of anti-Dombrock and confirmed glycosylphosphatidylinositol membrane attachment. Dombrock expression is developmentally regulated during erythroid differentiation and occurs at highest levels in the fetal liver. Homology studies suggest that the Dombrock molecule is a member of the adenosine 5′-diphosphate (ADP)–ribosyltransferase ectoenzyme gene family. Genotypic comparisons suggest Doa versus Dob antigenicity results from a single amino acid substitution within an encoded arginine-glycine-aspartic acid (RGD) motif of the molecule.

Assessment of the clinical significance of anti-Dob

BACKGROUND

Anti-Dob is an uncommon antibody, and there are few data regarding its clinical importance. In the present case, the patient's transfusion management was based on both in vivo and in vitro assay results.

CASE REPORT

A delayed hemolytic transfusion reaction was suspected in a 64-year-old white woman awaiting cardiac surgery when the transfusion of 1 unit of red cells failed to raise her hematocrit. Although direct antiglobulin tests were negative, antibody screening tests on samples drawn 9 days after transfusion were positive, and anti-Dob was identified, reacting to a titer of 4. 51Cr in vivo survival studies with incompatible Do(b+) red cells showed poor survival: 83.2 percent at 1 hour, 43 percent at 24 hours, and 29.6 percent at 48 hours and t1/2 = 19 hours (normal t1/2 = 25-35 days). A monocyte monolayer assay performed with the same incompatible Do(b+) donor red cells also indicated poor survival: 22 percent and 30 percent reactive monocytes, respectively, with and without the addition of complement (normal, 0-3%). The patient was given 4 Do(b-) red cell units without clinical signs or symptoms of a reaction.

CONCLUSIONS

This example of anti-Dob was implicated in a delayed hemolytic transfusion reaction. The 51Cr survival studies and monocyte monolayer assay results indicated that the anti-Dob was clinically significant, requiring the use of Do(b-) red cells for transfusion.

Chromosome location of genes encoding human blood groups

The chromosomal locations of genes controlling the expression of some 200 antigens constituting the 23 established human blood group systems have been reviewed. Twenty-one of the these genes are located on 12 autosomes, and two are located on the X chromosome. Refined chromosomal positions, to a single cytogenetically distinguishable band, have been established for 13 of the 23 genes. For the remainder, continued investigation will achieve the same result. The genes (RD, MER2, and OK) controlling the expression of one low-incidence and two high-incidence erythrocyte antigens have also been presented. Of these, OK is the most likely candidate for blood group system status, because its chromosomal location distinguishes it from all established system genes except LE and LW, and, the product of the OK gene is different from those of LE and LW (Table 3). This issue will be considered at the next meeting (scheduled for July 1998) of the ISBT Working Party. Alternatively, RD and MER2 are not good candidates for blood group system status because RD and MER2 reside in chromosomal regions containing genes for other blood group systems. In addition, the products of RD and SC have similar biochemical characteristics, and the product of MER2 has not yet been defined (Table 3). The challenge remaining for blood group scientists is characterization of genes that control expression of the approximately 50 other known erythrocyte antigens. Most of these are members of the ISBT's 700 (low-incidence) or 901 (high-incidence) series. Because the current genetic information for each of these antigens (attained by serologic investigation) varies considerably, future studies will have to rely on "tools" from related disciplines to provide the additional information. Use of resources such as molecular biological protocols and GBD should facilitate the effort.