MN and Ss Blood Group Systems

Cards (38)

  • 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