MN and Ss Blood Group Systems

• MNSs System

  • The M antigen and N antigen were discovered to be alleles
  • The S antigen was discovered to be genetically linked to MN
• MNSs system

  • Little s is the allele of S
  • U (universal) antigen was discovered later
  • There are 49 antigens in the MNSs group
• The MNSs system was the second human blood group to be discovered
• MN

  • MN are antithetical antigens
  • they are co-dominant, you inherit one allele from each parent
  • MN are affected by dosage
• antithetical - affected by dosage
• MN can be inherited as MM, MN, or NN (3)
• MN antigens

  The MN antigens are found on a glycoprotein called MN-sialoglycoprotein (MN-SGP) or glycophorin A (GPA)
• MN antigens

  • the antigens exhibit dosage
  • MM people carry a double dose of M and react mroe strongly with anti-M than people with MN
• MN antigens

  • antigens can be detected as early as 9 weeks gestation, and are fully developed at birth
  • paternity test
• MN antigens

  • the antigens are on the outer end of GPA so they are easily destroyed by blood bank enzymes -- ficin, papain, bromelain
• MN antigens

  • detected on RBCs
• MN antigens

  • GPA is restricted to RBCs and is often used as an erythroid marker
  • a GPA-like molecule has been detected on the renal endothelium
• Ss antigens

  • Ss antigens are located on a smaller glycoprotein that is very similar to MN
  • SS-sialglycoprotein (SS-SGP) or glycophorin B (GPB)
  • The amino acid at position 29 on GPB is critical to antigen expression
  • S = methionine
  • s = threonine
• Ss antigens

  • Ss antigens exhibit dosage
  • they are co-dominant alleles
  • appear at 12 weeks gestation and are well developed at birth
• Ss antigens

  • Ss antigens are not so easily degraded by enzymes because the antigens are located further down on the glycoprotein
• Ss antigen

  • they will be degraded with stronger concentrations of ficin and papain
  • They are definitely degraded by bleach
• S-s-U-

  • seen in 2% of blacks and a higher proportion of Black Africans
  • U antigen is a high frequency antigen in the general populatin
  • 99% of white pop and 95% of black pop
• U antigen is resistant to denaturation by proteases (ficin, papain, trypsin...)
• GPA and GPB

  • GPA and GPB are exploited by Plasmodium falciparum as receptors for binding to RBCs and may be critical to the invasion process
  • Because of this, people from ethnic groups where this parasite is endemic are more likely to be negative for S and s antigens than any other population
• Other MNS antigens

  • Mur antigen is a form of M
  • it is relatively common in Southeast Asia
  • rare in whites and blacks, but has a prevalence of 7% in Chinese and 10% in Thai
• Other MNS antigens

  • anti-Mur is the most common blood group antibody after anti-A and anti-B in Hong Kong and Taiwan
• anti-Mur has the potential to cause HTRs and HDFN (2)
• MN antibodies

  • anti-M are generally IgM and are naturally occurring
  • anti-N is very rare
• MN antibodies

  • most anti-M and anti-N are not active at 37 degrees
  • They are not clinically significant, can ignore
  • some can be active at 37 degrees and when encountered, antigen negative cells should be used
• MN antibodies

  • anti-M has very rarely been responsible for HDFN
  • rarely anti-M and anti-N have been implicated in acute and delayed HTRs
• MN antibodies

  autoanti-N can cause warm AIHA
• MN lectins

  N reactivity - Bauhinia variegate, B candicans, B bonatiana, B purpura (4)
• MN lectins

  M reactivity - seeds from Iberis amar, I umbellate, I semperivens (3)
• Ss antibodies - anti-S, anti-s, and anti-U are immune antibodies
• Ss antibodies are usually IgG
• Ss antibodies are active at 37 degrees C
• Ss antibodies have been implicated at HTRs and in severe and fatal HDFN
• autoanti-S can cause AIHA
• if immunized, individuals with S-s-U- red cells may produce anti-U
• anti-U can cause HTR, HDFN, and AIHA (3)
• antibody comparison

  anti-M and anti-N

  • naturally occuring
  • cold IgM
  • dosage matters
  • insignificant
• antibody comparison

  anti-S, anti-s, and anti-U

  • requires exposure
  • warm IgG
  • minimal dosage
  • significant
• AIHA is autoimmune hemolytic anemia