Transfusion medicine

Red blood cell antigens

MNSU system


Editorial Board Member: Kyle Annen, D.O.
Deputy Editor-in-Chief: Patricia Tsang, M.D., M.B.A.
Brian D. Adkins, M.D.
Garrett S. Booth, M.D., M.S.

Topic Completed: 8 September 2021

Minor changes: 8 September 2021

Copyright: 2020-2021, PathologyOutlines.com, Inc.

PubMed Search: MNS blood group system[TIAB]

Brian D. Adkins, M.D.
Garrett S. Booth, M.D., M.S.
Page views in 2020: 8
Page views in 2021 to date: 82
Cite this page: Adkins BD, Booth GS. MNSU system. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/transfusionmedMNSUsystem.html. Accessed December 3rd, 2021.
Definition / general
  • MNSU blood group system is antigenic on the surface of red blood cells (RBC)
  • Antibodies to M and N are generally clinically insignificant
  • Antibodies to other antigens, such as S, s and U, are clinically significant
Essential features
  • Antibodies to M and N are generally clinically insignificant
  • Antibodies to other antigens, such as S, s and U, are clinically significant
  • There are numerous high frequency and low frequency antigens, some of which are clinically significant
Terminology
  • M (MNS1), N (MNS2), S (MNS3), s (MNS4)
  • U (MNS5) or universal
  • Glycophorin A (GPA, CD235A)
  • Glycophorin B (GPB, CD235B)
Antigens

Race / ethnicity M+N- M+N+ M-N+ M-N- S+s- S+s+ S-s+ S-s-
White 30% 49% 21% Rare 10% 42% 48% Rare
Black (U.S.) 25% 49% 26% Rare 6% 24% 68% 2%

Antibodies
  • Antibodies to M and N are usually cold reactive, not clinically significant and naturally occurring, while S, s and U antibodies are clinically significant
  • M antibodies tend to be IgM and are generally not associated with hemolytic disease of the fetus and newborn (HDFN) (rarely reported), though assessment for IgG conversion should be considered (AJP Rep 2017;7:e205)
  • N antibodies are generally IgM
  • S, s, U and other antibodies tend to be IgG and can cause hemolytic transfusion reactions and HDFN (Fung: Technical Manual, 19th Edition, 2017)
  • N antigen exists on the N terminus of the glycophorin A peptide, similar to the N terminus of all glycophorin B peptides; hence antibodies against N are less common (Fung: Technical Manual, 19th Edition, 2017)
  • Mur antibodies are common in Southeast Asia (Fung: Technical Manual, 19th Edition, 2017)
Pathophysiology
  • Antibodies to M can form naturally without exposure, with auto anti-M commonly encountered
  • S, s and U antibodies are clinically significant
  • Exposure to antigens can lead to sensitization
  • Reference: Fung: Technical Manual, 19th Edition, 2017
Clinical features
  • African Americans have a deletion in the coding region of GYPB and can form antibodies against S, s and U (a high prevalence antigen)
    • High prevalence of U antigen and scarcity of U negative donors render management of patients with anti-U challenging
  • Presence of an N antibody suggests a lack of glycophorin B and may indicate patients can form anti-U antibodies
  • Reference: Fung: Technical Manual, 19th Edition, 2017
Transmission
  • Exposure to MNS antigens secondary to pregnancy or transfusion
Laboratory
Case reports
Board review style question #1
A gravida 1 para 0 mother is found to have an anti-M antibody. The clinical team wants to determine if the antibody is IgG or IgM. Treatment of the patient serum with which reagent destroys IgM antibodies and helps to determine if this is an IgG antibody?

  1. Addition of antihuman globulin
  2. Dithiothreitol (DTT)
  3. Enzyme treatment
  4. Polyethylene glycol (PEG) enhancement
Board review style answer #1
B. Dithiothreitol (DTT)

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Reference: MNSU system
Board review style question #2
A Jehovah's Witness patient agrees to receive plasma products only. A type and screen is found to be positive. The patient is disturbed when he sees this result in the patient portal, as he has no transfusion history. What is the best explanation to provide to the patient?

  1. He has likely been transfused with RBCs at some point and this is evidence
  2. These antibodies can be naturally occurring
  3. This is likely passive transfer from his recent FFP transfusion
  4. This patient needs a RBC transfusion
Board review style answer #2
B. This could be a naturally occurring anti-M antibody

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Reference: MNSU system
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