Red Cell Antigens Trivia Quiz

Answer: N-acetyl-D-galactosamine

D-galactose is the B antigen. Both A1 and B are part of the ABO blood group system, the most important in transfusion medicine.
Acetylcholinesterase, an enzyme primarily known to degrade acetylcholine, exists as a dimer on the red cell surface and forms what is known as the Cartwright antigen. The Cartwright blood system has two antithetical antigens, Yt(a) and Yt(b), formed by an amino acid substitution at position 353 of histidine (Yt(a)) and asparagine (Yt(b)). The enzyme is active on the red cell membrane, however its function in this setting is unknown.
As a trivia note, a form of acetylcholinesterase is found in the Pacific Torpedo ray, Torpedo californica.
Glycophorin A is one half of the MNSs (more strictly, the MNS) blood group system, the M and N antigens. Glycophorin B forms the S and s antigens. The M and N antigens are a result of two amino acid substitutions. The M antigen has a serine and glycine and positions 1 and 5, respectively, while the N antigen has leucine and glutamic acid.

Answer: CD44

The Indian blood group system is named from the distinct phenotype found on 4% of the population in India. It comprises of two antithetical antigens, In(a) and In(b), and is carried on the CD44 glycoprotein. CD (cluster of differentiation) markers are used to identify cell surface antigens on leukocytes, though these markers are present on cells of haematopoietic lineage. CD44 is involved in cell-to-cell interactions, cellular adhesion and migration.
The Kell and Kidd glycoproteins are the components of the Kell and Kidd blood group systems, respectively.

Answer: Rh blood group system

The Rh blood group system consists of five main distinct antigens, D, C, c, E and e. All are highly immunogenic (that is, they elicit an immune response in a high number of cases of exposure/immunisation), especially the D antigen. They can cause haemolytic disease of the newborn and severe haemolytic transfusion reactions.
The Kell blood group system comes in right behind the Rh system in its clinical significance. The Kell system consists of five sets of antigens, but the primary concern in transfusion practice is the K (Kell) antigen, which has a prevalence of 9% in Caucasian populations and 2% in African American populations. Like the Rd (D) antigen, it is highly immunogenic and can cause haemolytic disease of the newborn and severe transfusion reactions.
As another trivia note, the Kell antigen only appears in humans, while the antithetical k (cellano) antigen appears on the red cells of lower primates as well as in humans.
The Colton blood group system is of little consequence in the majority of cases. There are three antigens in the Colton blood group system called Co(a), Co(b) and Co3. Co(a) is found in 99.9% of the population, Co(b) 10% and Co3 on all red cells except those of the very rare phenotype Co(a-b-). As a result of the low incidence of the Co(b) phenotype, it is rarely an issue in transfusion practice.
The Lewis blood group system is an unusual system in that the antigens are not attached to the red cell surface. They are instead adsorbed on to the red cell surface. In addition, as opposed to other blood group systems, the two antigens Le(a) and Le(b) are not alternate forms of a single gene. Le(b) is an enzyme modified form of Le(a).

Answer: H antigen

The Bombay phenotype was first discovered in Bombay, India and describes the extremely rare condition where a person lacks the H antigen. It is limited to South East Asian countries (at the time of current research) and has an incidence of 1 in 250,000 persons.
The H antigen is the precursor antigen for both A and B antigens, where A and B enzymes modify the H antigen to form A and B respectively. H antigen is the component of ABO blood group O red cells, though is undetected and referred to as an absence of A and B antigens in routine testing.
The I antigen is the subterminal portion of the H antigen from the red cell surface. It is an late modified form of the i antigen which exists on foetal red cells and persists until two years of age. The i antigen is then modified from its straight chain appearance to the branched I antigen. As this occurs after the immune system has begun to function, I antigen is not recognised as a self antigen and the body forms auto-anti-I in response. Generally the autoantibody is benign and only functions at low temperatures (that is, it is a cold agglutinin). I antigen is clinically significant only where the autoantibody is reactive at room temperature.
A and B antigens are the determinants of the ABO blood groups A and B.

Answer: Lewis and Chido/Rodgers antigens

Lewis antigens are carbohydrate molecules formed in the intestinal epithelium. These circulate in the plasma and are passively adsorbed onto the red cell membrane. Chido/Rodgers antigens are in fact complement protein bound to the red cell membrane. In complement activation in the classical pathway, C4 is bound to the red cell membrane before undergoing further cleavage. The C4d fragment forms the Chido/Rodgers antigen.
The other antigens named are real antigens.

Answer: A variant form of a known antigen

ABO blood group subtypes are extremely important in transfusion medicine.
The most commonly seen in clinical practice (and it is rare, at that) is the A subgroup A2. In Caucasian populations, 77% of individuals of group A are A1 with the remainder being A2, compared to 75% of group AB being A1B with the remainder A2B. While the statistics remain the same in African American populations for A1B versus A2B, only 70% of individuals of group A are A1 and the remainder A2. However, African American populations have a much higher incidence of ABO types B and O (19% B and 49%O) when compared against Caucasian populations (9%B and 44% O). In Asian populations A2 is extremely rare.
The difference between the antigens is both quantitative and qualitative. A2 cells have a lower number of antigens than A1 cells and the oligosaccharide branching is different between the two antigens. These subtypes are important in transfusion science as A2 and other subgroups of A (A3, A(el) and Ax) can form anti-A1, causing a ABO reverse group discrepancy on testing and a delay in transfusion as anti-A1 will react with the majority of group A units.
There are fewer B subtypes and consequently fewer issues associated with transfusion medicine.

Answer: The surname of the first person to show antibodies to the antigens

Many of the blood group systems discovered in clinical practice were named from the last name of the patient who first showed antibodies to the antigen system. As transfusions become a common occurrence, so too did the appearance of antibodies to previously unknown antigens. Mr Duffy was a haemophiliac who had received multiple transfusions and developed what was soon known as anti-Fy(a) as a result.

Answer: Modification of the A antigen to form a B antigen by bacterial enzymes

The acquired B phenotype is well documented in blood banking. It has two possible mechanisms. One is the modification of the A antigen (N-acetyl-D-galactosamine) by bacterial deacetylase to form the B antigen (D-galactose) and the other is the production of a B-like substance from Escherichia coli O21 which is adsorbed to the red cell surface. Both types give a weak forward grouping with anti-B reagents and the individual will have a reverse group according to their actual ABO group. An acquired B phenotype is only detectable with certain monoclonal antisera and the majority in use in blood banking today are those reagents which do not detect acquired B.

The acquired B phenotype occurs in cases where bacteria from the intestine enter the circulation in cases of colorectal carcinoma, intestinal obstruction or severe Gram-negative sepsis. As a trivia aside, there has been a case where the detection of an acquired B phenotype led to the diagnosis of a previously unknown colon carcinoma in a patient.

Answer: Duffy

The Duffy blood group system has two antithetical antigens, Fy(a) and Fy(b). Individuals are either Fy(a+b-), Fy(a+b+), Fy(a-b+) or the rarer Fy(a-b-). This last phenotype occurs predominantly areas where the P. vivax is endemic as the null phenotype (that is, one which lacks the antigens entirely) provides resistance to malarial invasion.
The Duffy antigen is not solely the receptor for P. vivax, of course, but is a chemokine receptor.

Answer: Kell antigen

McLeod syndrome is a disease which affects males more than females. It involves muscular and neurological defects including skeletal muscle wasting, cardiomyopthy, late onset dementia, peripheral neuropathy, facial tics and seizures. The XK gene is missing or has deletions in its sequence.

The gene is located on the X chromosome and lyonisation in females is thought to account for the lesser severity. The first symptoms appear after the fourth decade of life. Lyonisation is the inactivation of one X chromosome in mammalian cells by packaging the inactivated X chromosome in heterochromatin.

In higher mammals the inactivation persists for the life of the cell and is random as to either maternal or paternal X inactivation. In marsupials, the X inactivation is confined solely to the paternal X chromosome.