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