Medicine:MNS antigen system

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Short description: Human blood group classification

The MNS antigen system is a human blood group system based upon two genes (glycophorin A and glycophorin B) on chromosome 4. There are currently 50 antigens in the system,[1][2][3][4] but the five most important are called M, N, S, s, and U.

The system can be thought of as two separate groups: the M and N antigens are at one location on the ECM and S, s, and U are on a closely related location. The two groups are very closely located together on chromosome 4 and are inherited as a haplotype.

The MN Blood Group

The MN blood group system is under the control of an autosomal locus found on chromosome 4, with two alleles designated LM and LN. The blood type is due to a glycoprotein present on the surface of a red blood cell (RBC), which behaves as a native antigen. Phenotypic expression at this locus is codominant because an individual may exhibit either one or both antigenic substances. Frequencies of the two alleles vary widely among human populations.[5]


The U and Ss groups: an overview

Other MNS antigens

The other 41 identified antigens in the MNS group are low incidence, such as He (0.8% of the population) or high incidence, such as ENa (>99.9% of the population).

MNS glycoproteins and genes

Antigens of the MNS system are located on one of two glycoproteins: glycophorin A (GPA, CD235A) and glycophorin B (GPB, CD235B).[6] Each glycoprotein crosses the membrane once and has an external N-terminal domain (varying in length from 44 amino acids for GPB to 72 amino acids in length for GPA)[6] as well as a C-terminal cytosolic domain (GPB, 8 amino acids in length; GPA, 36 amino acids in length).[6]

Clinical diagnostic

Clinical testing in patient care for MNS antigens follows published minimum quality and operational requirements,[7] similar to red cell genotyping for any of the other recognized blood group systems. Molecular analysis can identify gene variants (alleles) that may affect MNS antigens expression on the red cell membrane.

MNS antibodies

Interpretation of antibody panel to detect patient antibodies towards the most relevant human blood group systems, including MNS.
  • MNS antibodies display dosage (they react stronger against cells which are homozygous vs heterozygous for the antigen in question).
  • Anti-M and anti-N antibodies are naturally occurring, cold-reacting IgM-class antibodies.[8]
  • Anti-M and anti-N are generally clinically insignificant.
  • Anti-S, anti-s and anti-U antibodies are acquired following exposure (via pregnancy or past transfusion with blood products) and are warm-reacting IgG-class antibodies.[8]
  • Anti-S, anti-s and anti-U are usually clinically significant.

References

  • https://www.mun.ca/biology/scarr/MN_bloodgroup.html
  • Mark E. Brecher, Editor (2005), AABB Technical Manual, 15th edition, Bethesda, MD: AABB, ISBN 1-56395-196-7, p. 336-340
  • Denise M. Harmening (1999), Modern Blood Banking and Transfusion Practices, Philadelphia, PA: F.A. Davis Company, p. 164-169
  1. ↑ Daniels G, Flegel WA, Fletcher A, et al. International Society of Blood Transfusion Committee on Terminology for Red Cell Surface Antigens: Cape Town Report. Vox Sang 2007; 92: 250-3.
  2. ↑ Poole J, Daniels G. Blood Group Antibodies and Their Significance in Transfusion Medicine. Transfus Med Rev 2007; 21: 58-71.
  3. ↑ Daniels G. Human Blood Groups. 2nd Ed. Oxford: Blackwell Science, 2002.
  4. ↑ ISBT Committee on Terminology for Red Cell Surface Antigens. "Table of blood group antigens within systems". International Society for Blood Transfusion. Archived from the original on 2011-08-18. https://web.archive.org/web/20110818062517/http://ibgrl.blood.co.uk/ISBTPages/ISBTTerminologyPages/Table%20of%20blood%20group%20antigens%20within%20systems.htm. Retrieved 2010-01-24. 
  5. ↑ Ralph H. Kathan and Anthony Adamany. 1967. Comparison of Human MM, NN, and MN Blood Group Antigens. The Journal of Biological Chemistry, 242, 1736-1722.
  6. ↑ 6.0 6.1 6.2 Roback JD et al. AABB Technical Manual, 16th Ed. Bethesda: AABB Press, 2008.
  7. ↑ "Association for the Advancement of Blood & Biotherapies (AABB). (2025). Standards for molecular testing for red cell, platelet, and neutrophil antigens, 7th ed. (ISBN: 978-1-56395-516-7)". https://www.aabb.org/aabb-store/product/standards-for-molecular-testing-for-red-cell-platelet-and-neutrophil-antigens-7th-edition-print-18521318. 
  8. ↑ 8.0 8.1 Mais DD. ASCP Quick Compendium of Clinical Pathology, 2nd Ed. Chicago: ASCP Press, 2009.



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