This work was supported by a grant from Taiwan National Science Council (NSC 99-2320-B195-001-MY3) and by Mackay Memorial Hospital to K.H.
STATE OF THE ART†
Physiological Implications of Miltenberger blood group antigen subtype III (Mi.III)
Article first published online: 20 OCT 2011
© 2011 The Author(s). ISBT Science Series © 2011 International Society of Blood Transfusion
ISBT Science Series
Special Issue: State of the Art Presentations, 22nd Regional Congress of the ISBT – Asia, Taipei, Taiwan, November 19–23, 2011
Volume 6, Issue 2, pages 302–305, December 2011
How to Cite
Hsu, K. (2011), Physiological Implications of Miltenberger blood group antigen subtype III (Mi.III). ISBT Science Series, 6: 302–305. doi: 10.1111/j.1751-2824.2011.01504.x
- Issue published online: 20 OCT 2011
- Article first published online: 20 OCT 2011
- band 3;
- gas exchange;
- glycophorin A;
- glycophorin B;
- Miltenberger blood group antigen subtype III;
In Taiwan, Miltenberger blood group antigen subtype III (Mi.III) is the second most important blood group antigen following ABO. Mi.III presumably evolved from homologous recombination between GYPA and GYPB, and expresses a hybrid configuration of glycophorin B-A-B and the Mur antigen in the crossover region.
GPA and GPB oligomerize on the erythrocyte cell membrane. GPA also forms protein complexes with band 3 and facilitates band 3 expression. GPB is believed not to involve in the GPA-band 3 interaction. In Mi.III+ blood, half or all GPB is replaced with the glycophorin BAB hybrid, Gp.Mur. We previously showed that upon heterologous expression in HEK-293 cells, Gp.Mur, like GPA, facilitates the protein expression of band 3. Quantitative proteomics by iTRAQ revealed 25–67% more band 3 on the Mi.III+ erythrocyte membrane, as compared to the non-Mi.III. Band 3 is a Cl−/HCO3− exchanger. With more band 3 protein expression, Mi.III+ RBCs exhibit larger capacities for Cl−/HCO3− exchange across the cell membrane. Conceivably, those with the Mi.III phenotype might have larger capacities for CO2 respiration.
On the other hand, GPB is a component of the Rh protein complex, and has been shown to assist the surface expression of RhAG. Because GPB is half or completely replaced by Gp.Mur in Mi.III+ RBCs, we also examined if the expression of the Rh complexes could be affected in Mi.III. We found that homologous Mi.III RBCs exhibit reduced levels of RhAG and Rh antigens. The functions of Rh polypeptides and RhAG in erythrocytes are unclear, but RhAG in other species might function as gas channels for physiologically important molecules such as CO2, NH3, NO, and/or O2. Thus, substitution of GPB with Gp.Mur in Mi.III+ RBCs affects the structure of the band 3/Rh-associated macrocomplex, and is expected to affect functional coordination within the metabolon of O2/CO2 gas exchange as well.