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Storry, J.R.

18 IMMUNOHEMATOLOGY, Volume 37, Number 1, 2021
This update of the Ok (OK) blood group system (Smart EA, Storry 
JR. The OK blood group system: a review. Immunohematology 
2010;26:124–6) focuses on new information on the role of basigin 
(BSG), the carrier molecule of the Ok blood group antigens. No 
further antigens have been identified since the original review. 
However, the role of BSG in malaria continues to be explored. 
Immunohematology 2021;37:18–19.
Summary of the Ok Blood Group Antigens
To date, the Ok blood group system, system 24 in the 
International Society of Blood Transfusion (ISBT024), 
comprises three high-prevalence antigens: Oka, OKGV, 
and OKVM. Only one example of the OKGV− and OKVM− 
phenotypes has been described, each identified by the 
presence of a specific antibody to its respective high-prevalence 
antigen.1,2 The Ok(a−) phenotype was identified in Japanese 
people only,3 and the allele frequency in the gnomAD database 
is 0.1 percent in the so-called East Asian population.4 Table 1 
shows a summary of information regarding the Ok blood 
group system antigens.
The Ok antigens are carried on basigin (CD147, extra-
cellular matrix metalloproteinase inducer [EMMPRIN]), a 
single-pass membrane protein and member of the immuno-
globulin (Ig) superfamily. There are two primary isoforms of 
basigin (BSG); the first (BSG1) is a longer protein of 385 amino 
acids and three Ig domains, which is found in the retina. The 
shorter, more widely distributed isoform (BSG2) of 269 amino 
acids and two Ig domains is found on red blood cells (RBCs) 
and is commonly referred to as BSG.5 BSG interacts with a 
number of proteins in the membrane. It has been shown to 
bind directly to members of the monocarboxylate transporters 
and act as a chaperone to the membrane for these proteins. In 
addition to its interaction with monocarboxylate transporters, 
BSG forms a lipid raft–associated complex in the membrane 
with CD44, glucose transporter 1 (GLUT1), and the epidermal 
growth factor (EGF) receptor. For further details on the 
function of BSG, the interested reader is referred to the review 
by Muramatsu.5
Role of BSG in Infectious Disease
The role of BSG as an adhesion molecule and its role in the 
stimulation of tumor growth and invasion were discussed in 
the original review.6 BSG was also shown to be an important 
receptor for a number of pathogens. Pushkarsky et al.7 showed 
20 years ago that BSG facilitated human immunodeficiency 
virus 1 (HIV-1) infection by interacting with virus-associated 
cyclophilin A and that the cytoplasmic region of the protein 
was important for enhancing HIV-1 replication.8
Measles virus–associated cyclophilin B was shown to bind 
to BSG on epithelial cells. Although leukocytes are the primary 
target for the virus, other tissues are known to be infected. 
Watanabe et al.9 showed that virion-incorporated cyclophilin 
B bound to BSG and hypothesized that this interaction could 
account for symptoms such as pneumonia and diarrhea in 
measles-infected patients.
Blood gRoup Revie w
The Ok blood group system: an update
J.R. Storry
Table 1. A summary of information regarding the three known Ok blood group system antigens
Phenotype ISBT allele name
Nucleotide 
change in BSG Exon
Predicted amino 
acid change Reference rs number Identified in
Occurrence in  
gnomAD4
OK:1 or  
Ok(a+)
OK*01.01†
OK:–1 or  
Ok(a–)
OK*01.–01 c.274G>A 4 p.Glu92Lys 3 rs104894669 Japanese East Asian 0.1%
OK:–2 or  
OKGV– 
OK*01.–02 c.176G>T 2 p.Gly59Val 1 rs1023817527 Iranian No data
OK:–3 or 
OKVM–
OK*01.–03 c.178G>A 2 p.Val60Met 2 rs2229662 Hispanic European 0.005%
† OK*01.01 encodes Oka, OKGV, and OKVM. Nucleotide changes are based on transcript basigin (BSG)-203 (ENST00000353555.9; https://www.ensembl.
org/Homo_sapiens/Gene/Summary?db=core;g=ENSG00000172270;r=19:571277-583493;t=ENST00000353555). ISBT = International Society of Blood 
Transfusion; gnomAd = Genome Aggregation Database.
DOI: 10.21307/immunohematology-2021-004
brought to you by COREView metadata, citation and similar papers at core.ac.uk
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IMMUNOHEMATOLOGY, Volume 37, Number 1, 2021 19
In 2011, an elegant and systematic screening identified 
BSG as an important receptor for the malarial parasite, 
Plasmodium falciparum, binding to the Rh5 ligand.10 The 
PfRh5 protein is important for commitment and invasion 
into the RBC, so identification of the RBC ligand was an 
important finding. Interestingly, Ok(a−) RBCs showed a 
weaker binding affinity for PfRh5 and were not as easily 
invaded by P. falciparum. Aniweh et al.11 have shown that the 
PfRh5–BSG interaction leads to Ca2+ signaling, downstream 
phosphorylation, and transient remodeling of the RBC 
membrane.
In addition to its important role in malarial infection, BSG 
was recently implicated as an alternative binding partner for 
the SARS-CoV-2 virus responsible for COVID-19.12–14
In summary, although there are few variants of BSG 
that appear to be immunogenic and give rise to blood group 
antigens, our understanding of the role of BSG in health and 
disease is expanding.
References
 1. Karamatic Crew V, Daniels G, Poole J. A new variant in the Ok 
blood group system. Transfus Med 2003;13(Suppl 1):32.
 2. Karamatic Crew V, Thomas B, Gillen B, Poole J, Daniels G. 
A novel variant in the Ok blood group system. Transfus Med 
2006;16(Suppl 1):41.
 3. Spring FA, Holmes CH, Simpson KL, et al. The Oka blood 
group antigen is a marker for the M6 leukocyte activation 
antigen, the human homolog of OX-47 antigen, basigin and 
neurothelin, an immunoglobulin superfamily molecule that is 
widely expressed in human cells and tissues. Eur J Immunol 
1997;27:891–7.
 4. Karczewski KJ, Francioli LC, Tiao G, et al. The mutational 
constraint spectrum quantified from variation in 141,456 
humans. Nature 2020;581:434–43.
 5. Muramatsu T. Basigin (CD147), a multifunctional trans-
membrane glycoprotein with various binding partners. J 
Biochem 2016;159:481–90.
 6. Smart EA, Storry JR. The OK blood group system: a review. 
Immunohematology 2010;26:124–6.
 7. Pushkarsky T, Zybarth G, Dubrovsky L, et al. CD147 facilitates 
HIV-1 infection by interacting with virus-associated cyclo-
philin A. Proc Natl Acad Sci U S A 2001;98:6360–5.
 8. Pushkarsky T, Yurchenko V, Laborico A, Bukrinsky M. CD147 
stimulates HIV-1 infection in a signal-independent fashion. 
Biochem Biophys Res Commun 2007;363:495–9.
 9. Watanabe A, Yoneda M, Ikeda F, Terao-Muto Y, Sato H, Kai 
C. CD147/EMMPRIN acts as a functional entry receptor for 
measles virus on epithelial cells. J Virol 2010;84:4183–93.
 10. Crosnier C, Bustamante LY, Bartholdson SJ, et al. Basigin is 
a receptor essential for erythrocyte invasion by Plasmodium 
falciparum. Nature 2011;480:534–7.
 11. Aniweh Y, Gao X, Hao P, et al. P. falciparum RH5-basigin 
interaction induces changes in the cytoskeleton of the host 
RBC. Cell Microbiol 2017 Sep;19(9). doi:10.1111/cmi.12747. 
 12. Wang K, Chen W, Zhang Z, et al. CD147-spike protein is a novel 
route for SARS-CoV-2 infection to host cells. Signal Transduct 
Target Ther 2020;5:283.
 13. Ahmetaj-Shala B, Vaja R, Atanur SS, George PM, Kirkby 
NS, Mitchell JA. Cardiorenal tissues express SARS-CoV-2 
entry genes and basigin (BSG/CD147) increases with age in 
endothelial cells. JACC Basic Transl Sci 2020;5:1111–23.
 14. Ulrich H, Pillat MM. CD147 as a target for COVID-19 treatment: 
suggested effects of azithromycin and stem cell engagement. 
Stem Cell Rev Rep 2020;16:434–40.
Jill R. Storry, PhD, Technical Director, Immunohematology, Clinical 
Immunology and Transfusion Medicine, Department of Laboratory 
Medicine, Office for Medical Services, Akutgatan 8, SE-22185, Lund, 
Sweden, jill.storry@med.lu.se.
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