MNS Blood Group System Quiz

MNS Blood Group System

• Antithetical M and N antigens and antithetical S and s antigens exist.
• The U antigen is part of the MNS system and is exclusively found in African populations.
• Genetic inheritance mirrors the Rh system, with two pairs of closely linked alleles located on closely linked loci.
• The GYPA gene controls M and N antigens and GYPB controls S and s antigens.
• Antigens are found on glycophorins, which are transverse to the red cell membrane.
• Glycophorin A carries M or N antigens.
• Glycophorin B carries S, s, and U antigens.
• M and N antigens have similar frequencies.
• The s antigen is more frequent than the S antigen.

MNS Antibodies

• M and N antibodies (Ab) are mostly opposite to S, s, and U.
• Anti-M and Anti-N are often clinically insignificant unless they react at 37°C.
• Anti-S and Anti-s are less common as causes of reaction at 37°C.
• Anti-M is typically insignificant but can be associated with severe hemolytic disease of the newborn (HDN).
• The effect of Anti-M varies based on the enzyme, with enzymes typically decreasing all other MNS antigens except U.
• Most Anti-M, Anti-N, and Anti-s antibodies do not bind complement.
• Some Anti-S antibodies do bind complement.
• Antibody dosage is evident with Anti-M and Anti-N, but not so readily apparent with Anti-S and Anti-s.

P Blood Group System

• Antigens: P1 (has both P and P1 on cells), P2 (only P on cells), and p (no P or P1).
• High incidence, with variations in antigen strength amongst individuals.
• P1 antigens vary greatly in strength within P-positive individuals.
• P1 antigen deteriorates when blood is stored in vitro.
• P1 antigen expression originates from independently inherited genes.
• P1 antigen is produced by adding a galactose to a precursor chain.
• The GLOB gene converts Pk antigen to P antigen by adding N-acetylgalactosamine to the Pk antigen.
• The Pk gene adds galactose to a precursor chain.
• Mutations in the Pk gene can result in the p phenotype with no antigen expression.

P Phenotypes

• Most individuals produce antibodies (Ab) with P antigens that have poor expression at birth, improving later to age 7.
• P2 lacks P1, expresses Pk, and produces anti-P and anti-P1 antibodies in plasma.
• P1k lacks P antigen, expresses P1 and Pk, and produces anti-P1 antibodies in plasma.
• P2k expresses Pk, and produces anti-P and anti-P1 antibodies in plasma.
• The p phenotype lacks all P, P1, and Pk antigens and produces anti-P1, anti-p, and anti-Pk (or anti-Tja).

P Antibody Characteristics

• Anti-P1 is less common.
• Anti-P1 antibody formation is rarely stimulated by transfusions of P1 positive blood to a P2 individual.
• Anti-P is an example of a Donath Landsteiner antibody associated with paroxysmal cold hemoglobinuria.

P Clinical Significance

• Transfusion reactions are rare, occurring seldomly.
• P substances have been found in hydatid cyst fluid, worm extracts, fluke, fish roe, and pigeon serum, with some severity.
• Compound antibodies (Ab) may be formed with I blood system antibodies.
• Both antigens must be present before the antibody can react.

Lutheran Blood Group System

• Lua and Lub are codominant alleles.
• Lu is an amorphic allele.
• Lua and Lub are not fully developed at birth.
• Anti-Lua and Anti-Lub antibodies are not common.
• They can cause mild transfusion reactions or hemolytic disease of the newborn (HDN), uncommonly.
• Lua has low frequency and Lub high frequency.
• Most enzymes (e.g., 2ME or DTT) lower Lua antigen activity.

Lutheran Characteristics and Clinical Significance

• Anti-Luª antibodies are uncommon and not typically significant.
• Anti-Luª antibodies are usually IgM, reacting best at room temperature (RT) but sometimes reacting at 37°C.
• Anti-Luª antibodies usually do not bind complement.
• Anti-Lub antibodies can be IgM, IgG, or IgA, with the best reaction observed at 37°C using the indirect antiglobulin test (IAT).
• Anti-Lub antibodies are uncommon.

Xg Blood Group System

• The Xg gene is located on the X chromosome (X-linked).
• The Xg antigen is present in the majority of females (90%) and slightly fewer males (66%).
• Xg antibodies are generally not significant.
• The genes associated with this system are Xg and Xga.
• The Xga antigen is significant.

Xg Blood System Inheritance

• An Xg(a) male mating with an Xg female can produce offspring with various genotype combinations.
• All daughters are Xga+, while all sons are Xga-.
• Males are hemizygous for the Xg gene.

Xg Antibodies

• Xg antibodies are usually red blood cell (RBC)-immune.
• Most Xg antibodies bind complement.
• Xg antibodies are commonly detected by an antiglobulin test (AHG).
• HDN or transfusion reactions are rare despite the Xg antigen being well developed at birth.

High Incidence Antigens

• Antibodies against these antigens are rare but can cause difficulties in finding compatible blood units when they occur.
• These antigens are very present (>90%) in the European population.
• Examples include Cellano (k), Colton (Coa), Cartwright(Yta), Vel (V), Gerbich (Ge), and Sid (Sda).

Low Incidence Antigens

• Low incidence antigens occur less frequently (<1/1000).
• Examples include Levy, Wright (Wra), and Swann (Swa).
• Antibodies formed against these antigens usually don't cause practical problems in crossmatching.

High Titre Low Avidity Antibodies (HTLA)

• These antibodies show variable reactions with antiglobulin tests (AHGs), lacking true specificity.
• Reactions remain weak even at low dilutions.
• These antibodies are neutralized by group-specific substances (GSS), similar to soluble antigens.
• HTLA antibodies rarely cause hemolytic disease of the newborn (HDN) or transfusion reactions.
• Examples include Costerlin (Csa), York (Yka), Chido (Cha), Knops (Kna), McCoy (McCa), Holley (Hya), and Gregory (Gya).

HLA Antibodies

• These antibodies target antigens on white blood cells (WBCs).
• HLA antibodies are found in the plasma of patients with multiple transfusions or multiple pregnancies.
• HLA antibodies may bind complement.
• HLA antibody detection may produce nonspecific results.
• Common HLA antibodies include anti-Bgª and anti-Bgb.
• Transfusion reactions due to HLA antibodies can be severe, often accompanied by symptoms such as fever and respiratory distress.
• Patients with HLA antibodies who require transfusions should receive blood lacking WBCs to prevent reactions, and WBC-poor units are recommended.
• HLA antibodies are critical for organ donation compatibility and rejection prevention.

GPI-Linked Glycoprotein Antigens

• These antigens are rare.
• GPI-linked glycoproteins are deficient in patients with acquired hemolytic anemia, particularly paroxysmal nocturnal hemoglobinuria.
• These antigens may not express any antigens found on GPI-linked glycoproteins, such as JMH, Cartwright (Yt), Dombrock (Do), and Cromer (Cr).
• These deficiencies should not be confused with Paroxysmal Cold Hemoglobinuria (PCH).

Distinguishing Facts

• Chido/Rogers soluble antigens are found on the C4 complement component in plasma.
• Absorption of these antigens onto red blood cells (RBCs) occurs postnatally.
• Methods like chloroquine diphosphate or EDTA/glycine acid can dissociate immunoglobulin G (IgG) antibodies from RBCs.
• The expression of some antigens (e.g., Sid) varies among individuals, possibly decreasing during pregnancy; these can persist in bodily fluids like urine.
• Some antigens (e.g., V or Sid), though uncommon in Europeans, can be more common in other racial groups, and these may be clinically insignificant.
• Additional information can be found in separate course notes.

Test your knowledge on the MNS blood group system, focusing on the M and N antigens, as well as S and s antigens. This quiz covers key concepts, genetic inheritance, and the clinical significance of MNS antibodies within hematology. Dive into this unique blood group system and its components.