Lecture #3: THE BLOOD GROUP SYSTEM

Related blood groups are collected into group systems that are inherited independently of each other. Blood groups were first discovered on erythrocytes but are now known that almost all body fluids and tissue cells contain antigens. They are also found in animals, bacteria and plants.

In Genetics, the word system denotes a series of related phenotypes determined by allelic genes. In general, when a gene or set of allelic genes can be shown to segregate independently of all other genes responsible for other antigens, the set is designated a system. In most cases, epistatic genes are considered members of the same system as the genes that they affect even though unlinked to these genes.

A blood group system is composed of several antigens related to each other, whose incidence varies with one another.

Landsteiner Law:

Landsteiner Law states that antibodies are present in plasma only when the corresponding antigen is not present on the erythrocytes.

Notes to remember about blood group systems:

1. All saline agglutinins are IgM.

2. All warm agglutinins are IgG (antibodies that gives best reactions with albumin – suspended cells and by the antiglobulin technique).

3. All of the antibodies mentioned are clinically significant except anti–N and most examples of anti–I.

4. All IgG antibodies are immune.

5. All IgM antibodies are, or can be, naturally occurring.

6. Only Rh antibodies do not bind complement. ABO, Lewis and Kidd antibodies usually bind complement. The rest of the antibodies sometimes bind complement.

7. Only IgG antibodies cause hemolytic disease of the newborn.

The different blood group systems

1.  Principal Blood Group system

a.  ABO System (Click here for full discussion)

b.  Rh System (Click here for full discussion)

c.  MNSs

d.  Kell

e.  Duffy

f.   Kidd

g.  Lewis

h.  Lutheran

i.   I Blood Group System

j.   P Blood Group System

2.  Other blood group system

a.  Xg^a

b.  En^a

c.   Do^a,b (Dombrock)

^d.    Di^a,b

e.   Scianna (Sm–Burell)

f.    Yt^a,b (Cartwright)

g.   Wr^a(Wright)

h.   Vel

i.    Ge^a (Gerbich)

3.  High–Incidence (Public) Antigens

Antigens of high frequency are defined as occurring 99% of the population. All antigens not established to a major blood group system fall in this category.

a.  At^a (Augustine)

b.  Ch^a(Chido)

c.   Cs^a(Stirling)

d.   Kn^a (Knops–Helgeson)

e.    Sd^a (Sid)

f.     Cr^a (Cromer)

g.    Gy^a (Gregory)

h.    Hy (Holley)

i.     Jr^a (Jacobs

j.     Jo^a (Joseph)

k.    Lan (Langereis)

4.  Low–Incidence (Private) Antigens

These are antigens of low frequency or distribution that do not appear to belong to an established blood group system. To be placed in this category, an antigen must have an incidence of less than 1 in 400 of the general population.

a.   Be^a (Berrens)

b.   Bp^a (Bishop)

c.    Bx^a (Box)

d.    Gr^a (Griffiths)

e.    Ht^a (Hunt)

f.     Sw^a (Swann)

g.    By

h.    Mt^a (new antigen of MNSs blood group)

i.     Tr^a (Traversu)

5.    High–titer, Low Avidity (HTLA) Antigens

They exhibit reactivity at high dilutions of serum but weak agglutination at any dilution. This characteristic differs them from other blood groups that demonstrate progressively weaker reactivity with increased dilutions of the antibody–containing serum.

a.  Yk^a (York)

b.  McC^a (McCoy)

c.   Rg^a (Rodgers)

d.   JMH (John Milton Hagen)

Nomenclature

1. Some blood group antigens uses single letter in upper or lower case

e.g. A, C, D

2. Some blood group antigens uses a two letter combination with a superscript

e.g.  Fy^a, Le^b

3. When antigens are tested for and found to be present; the antigen symbol is followed directly by a plus sign or a minus sign when absent.

e.g. D⁺, K^–

4. When results of tests for antigens denoted by symbol with superscripts are written, the superscripts and (+) or (–) are put within parentheses.

            e.g.       Fy(a+), Jk (a–b+)

5. The prefix “anti” designates an antibody to the antigen which follows the prefix. This designation of the label of a vial of a reagent serum indicates the specificity of the antibody in the reagent.

e.g.  anti–D, anti–Fy^a

Terminology

1. Amorphic gene or silent gene – when currently available techniques are unable to detect the product of a gene.

2. Codominant – when the allelic genes of paired loci differ and both are expressed.

3. Polymorphic – when a blood group system has two or more alleles.

************  THE LEWIS SYSTEM  ************

1. This was discovered by Mourant in 1946.

2. Difference of Lewis system from other blood group

a. Erythrocytes acquired the Lewis phenotype by absorbing Lewis substances fro the plasma, rather than being membrane–bound antigens.

b. Although the Lewis and secretor genes are inherited independently, the Lewis phenotype is influenced by the secretor status.

c. The Lewis phenotype may be modified by the ABO phenotype (such as A₁) which may interfere with the expression of the Le^a antigen in Le(b+) individuals.

3. The Secretor Status

The terms secretor and non–secretor refer only to the presence of water–soluble ABH antigen substances in body fluids. This condition is influenced by the independently inherited regulator Se gene. The presence of Se gene allows the H gene to function in secretory cells.

These secretions have the property of reacting with their corresponding antibodies to neutralize or inhibit the ability of these antibodies to agglutinate erythrocytes possessing the corresponding antigen. This reaction is termed hemagglutination inhibibition and provides a means of assaying the relative activity or potency of these water–soluble blood group substances.

4. The red cells of adults have three possible Lewis phenotypes

a. Le (a+b–) – found in non–secretors, secrete Lea substance and has inherited sese gene

b. Le (a–b+) – found in secretors, secrete ABH, Lea and Leb substances and has inherited either SeSe or Sese gene.

c. Le (a–b–) – found in persons of genotype lele, these individuals are usually secretors.

5. Lewis types are determined by allelic genes Le and le while phenotypes depends on three independently inherited genes: Lele, Hh and Sese

a.  Presence of Le gene – production of Le^a substance

b.  Presence of Le, H and Se – production of Le⁵ substance

c.  Presence of two le genes – phenotype Le (a–b–)

6. Lewis antibodies

a. Anti–Le^a occurs in Lele secretor only.

b. Anti–Le^b occurs in two forms – Le^b1 and Le^bH

c. Anti–Le^x  is a specific agglutinin and is not a combination of anti–Le^a and anti– Le^b

7. Le (a–b–) blood should be given to subjects with Lewis antibodies

8. Lewis antibodies are common in pregnant woman who may type as Le (a–b–) while pregnant.

9. Saliva tests are more satisfactory than red cell tests for the detection of Lewis substance.

************  KELL BLOOD GROUP SYSTEM  ************

1. Discovered by Coombs, Mourant and Race in 1946.

2. Named after Mrs. Kelleher – the mother of newborn with HDN but not due to Rh

3.  Antigens

Original Names                                  New names

K (Kell)                                                      K1

k (Cellano,1949)                                    K2

Kp^a (Penney, 1957)                               K3

Kp^b (Rautenberg, 1958)                      K4

Ku (Peltz)                                                 K5

Js^a (Sutter, 1958)                                   K6

Js^b (Matthews, 1963)                           K7

K1 and K2 antigens are very antigenic and is after Rh antibodies, anti–K is the most commonly found. A total of 25 antigens have been discovered so far.

Ku is a universal Kell antigen present on all cells except K_o cells (K null phenotype)

4.  Antibodies

a.  Anti–K (K1) – naturally occurring IgM anti–K (K1) is rare, thought as an immune IgG antibody, it stands second in frequency to antibodies of the ABO and Rh systems, detected by antiglobulin technique at 37^oC, shows the ability to bind complement and has been implicated with HDN and HTR.

b.  Anti–k (K2) – a rare antibody, usually IgG,  detectable by antiglobulin technique; has been implicate in HDN & HTR and is always stimulated by transfusion or pregnancy

c.  Anti–Jsb – usually seen in black patients and seen in sickle cell disease patients with multiple alloantibodies.

5. McLeod Phenotype – a X–linked anomaly of the Kell blood group system in which Kell antigens are poorly detected by laboratory tests. The McLeod gene encodes the XK protein, a protein with structural characteristics of a membrane transport protein but an unknown function. The XK appears to be required for proper synthesis or presentation of the Kell antigens on the red blood cell surface. Mc Leod phenotype lacks Kx and Km antigens

6. Null phenotype – a rare phenotype (K_o) in which RBCs lack all Kell antigens. Individuals with this phenotype are healthy but produce anti–Ku when they encounter RBCs that do not express Kell antigens. Anti–Ku is capable of causing a mild to severe transfusion reaction with at least one fatal case being reported. Therefore, if K_o individuals ever requires a blood transfusion, they should be transfused with K_o blood products.

7.  DTT (dithiothreitol) and ZZAP (cysteine-activated papain and dithiothreitol) denature all Kell antigen except Kx.

************  DUFFY BLOOD GROUP SYSTEM  ************

1. Discovered by Cutbush, Mollison and Park in 1950.

2. Named after Duffy – the hemophilic who has received multiple transfusion

3. The gene giving rise to the Duffy antigen is called Fy^a and its allele Fy^b. Fy^a and Fy^b are codominant.

The Fy gene appears on the same chromosome as the genes of the Rh system but the loci of the genes are too far to be described as linked. The term “synteny” applies here, to be inherited on the same chromosome at are too apart to be inherited.

4. These antigens are protein in nature and are easily destroyed in vitro by proteolytic enzymes such as papain and ficin.

5. Phenotypes

Fy (a+b+) – common among Caucasian.

Fy (a–b–) – common among Blacks

The majority of Blacks are of this phenotype; these people are also resistant to Plasmodium vivax malaria. The membrane structure that carries the polymorphic antigens of the Fy system is apparently a receptor for P.vivax and without it the parasite cannot invade the erythrocyte.

6.          Antibodies

a. Anti–Fy^a – detected only in the antiglobulin test; usually IgG and has the ability to bind complement; has been implicated in HDN and HTR.

b. Anti–Fy^b – extremely rare antibody; usually IgG and has never been implicated in HDN but has been the cause of HTR.

************  KIDD (JK) BLOOD GROUP SYSTEM  ************

1.  Discovered by Allen and associates in 1951.

2.  Antigens

a.   JK^a

b.   JK^b

3. Antibodies

a.   Anti – JK^a

b.   Anti – JK^b

c.   Anti – JK^a JK^b

Kidd antibodies are usually IgG; detectable by the antiglobulin or enzyme technique; bind complement and have been implicated in HDN and HTR. Anti– JK^a exhibits dosage effects.

4. Kidd antigens are located on red blood cell urea transporter (a.k.a. human urea transporter 11 – HUT11 or UT–B1) and thus can transport urea at renal medulla.

************  MNSs BLOOD GROUP SYSTEM  ************

1.  Discovered by Landsteiner and Levine in 1927.

2.  Genotypes for M and N genes: MN, MM and NN

Phenotypes: M, MN and N

3. The gene S, although part of the system, is not allelic to M and N.

The gene s is an allele of S and the antigen S is found as frequently as MM as in NN European blood samples.

4.  N antigen is the precursor of M.

5.  Antibodies

a. Anti–M – rare IgM, cold agglutinin, naturally occurring IgG also occurs, does not have the ability to bind complement and has been implicated in HDN and HTR.

b. Anti–N – found as naturally occurring cold agglutinin of IgM type

c.  Anti–S – mostly immune IgG type but some naturally occurring IgM has been reported. Has the ability to bind complement

d. Anti–s – usually immune IgG type; binds complement and causes HDN & HTR.

6. Glycophorins are transmembrane, single–pass glycoproteins that contain carbohydrate, mostly in the form of sialic acid. Glycophorins A and B carry he MNS antigens and they may also serve as receptors for cytokines and pathogens including the malaria parasite, Plasmodium falciparum.

************ P BLOOD GROUP SYSTEM  ************

1.  Discovered by Landsteiner and Levine in 1927.

2.  Antigens

a.  P₁

b.  P₂

3.  Antibodies

a.  Anti–P₁ – present in 90% of pregnant P2 woman

b.  Anti–PP_1pK

c.  Anti–P

Antibodies are usually naturally occurring, IgM type and reacts best in saline suspended cells at 4^oC. Anti–P₁ and anti–PP_1pK have both been implicated in HTR.

************  Ii BLOOD GROUP SYSTEM  ************

1. Discovered by Wiener and associate in 1956 as specific cold agglutinin in person with hemolytic anemia; in 1960, Jenkins and associates discovered non–specific cold agglutinins to contain anti–I specificity.

2.  Antigens:

a. I–adult – the I antigen in random adults show a great range of strength. It may be considerably weakened in leukemia and altered by some virus.

b. i–cord – cord bloods vary in the amount of I antigen they contain.

c.  i–adult – extremely rare, contain trace amount of I antigen.

3.  Antibodies:

a.  Anti–I – an autoantibody, reacts best at cold temperatures. This antibody is the usual “cold agglutinin” found in high titers in the serum of patients with mycoplasma pneumonia

b. Anti–i – a cold agglutinin common in patients suffering from alcoholic cirrhosis or infectious mononucleosis; reacts best with saline suspended cells at cold temperatures; maybe IgG or IgM or both; has never been implicated in HDN & HTR.

************  LUTHERAN (LU) BLOOD GROUP SYSTEM  ************

1. Discovered by Callender and his associates in 1945.

2. Antigens:

a.  Lu^a

b.  Lu^b

3.  Antibodies:

a. Anti–Lu^a – extremely rare, occurring as a cold agglutinin; of IgM type and maybe natural or immune.

b. Anti–Lu^b – mainly in the IgA fraction though some appears to be IgM, detected by antiglobulin test, mostly of immunte type.

c.  Anti–Lu^a–Lu^b – usually immune IgM or IgA type.

************  OTHER BLOOD GROUP SYSTEM  ************

1. Xg

The Xga antigen is the only one controlled by a gene on the X (sex–linked) chromosome.  All others are controlled by genes on the autosomes. The Xg^a antigen is carried by 89% of females and 67% of males. The genotype of women may be Xg^a Xg^a, Xg^a Xg or XgXg but men can only be Xg^a or Xg. Men wo are Xg (a+) pass on Xg^a to all their daughters but transmit no Xg genes to their sons. The mating of an Xg (a+) man with a Xg (a–) woman must produce all Xg (a+) daughters and Xg (a–) sons.

Anti–Xg^a is an uncommon antibody and is reactive by indirect antiglobulin test. It has not been associated with HDN & HTR.

2. Sid

Sd^a, the only defined antigen in this system, is inherited as an autosomal dominant character and appears to be genetically independent of most other blood group systems. Rare cases have demonstrated an enhanced erythrocyte antigen, called Sd (a⁺⁺) or “SuperSid” and another form of Sd^a, named Cad, was originally thought to be a form of inherited polyagglutinability. This antigen is very difficult to work with because of a wide variation in antigenic expression; it is known to be weaker during pregnancy.

Sd^a substance is present in most body secretions. Four times as much Sd^a is found in the saliva of newborn infants as in the saliva of adults. Because the greatest concentration of Sd^a occurs in the urine, it is sometimes easier to categorize apparent weak Sd (a+) persons by testing their urine.

Anti–Sd^a is characteristically weakly reactive. Some Sd^a antibodies react at room temperature, 37^oC and AHG. Most examples of anti–Sd^a are demonstrable with enzyme–treated red cells and cells enhanced with LISS. Observable agglutinates have a characteristic refractile, mixed–field appearance. It is not associated with HDN & HTR.

The system was named Sid, after Mr. Sidney Smith of the Lister Institute, whose cells had, over many years; give the clearest positive reaction with the emerging glass of antibodies.

3. Cartwright

Most Whites are Yt (a+b–). The antibody is an immune antibody. Both anti–Yt^a and anti–Yt^b are usually reactive in AHG with LISS enhancement. Some examples are reactive in enzyme–enhanced red cell suspension.

4. Colton

The antigens are Co^a and Co^b. About 99% of the Whit population are Co (a+) and about 10% are Co (b+). American Blacks may have a lower incidence of Co (a–)

Anti–Co^a and anti–Co^b were identified in 1974. These antibodies are IgG in nature and have been associated with pregnancy with an incompatible fetus. Anti–Co^a can cause HDN and HTR while anti–Co^b can cause HTR only.

5. Diego

The antigens are Di^a (1955) and Dib (1967). All whites are Di(a–) and approximately 36% of certain of South American Indians are Di (a+). Five to fifteen percent of Japanese and Chinese are Di (a+).

Anti–Di^a reacts at room temperature, 37^oC and with enzyme enhancement. Most Di^a antibodies react in the AHG phase. Anti–Di^b generally reacts in AHG but some examples are reactive with enzyme–enhanced erythrocytes. Both antibodies have implicated in HTR and HDN.

6. Scianna

The SM antigen which occurs in almost all individuals was discovered in 1962. In 1963, anti–Bu^a was discovered and in 1964 t was suggested that two antigens, SM and Bu^a were products of allelic genes.

7. En^a

The cells of En (a–) individuals exhibit remarkable properties, particularly in that they have a marked deficiency in sialic acid, resulting in a reduction of their surface charge.

Situations in which antibodies against Erythrocyte Antigens can be found:

1. Naturally Occurring Isoantibodies

All people with component immune systems possess circulating antibodies against several red cell antigens. These naturally occurring antibodies are isoantibodies because they are directed against blood group antigens not present on the cells of the host. For example, person with type A blood has anti–B isoantibodies in his serum. Type O individuals have both anti–A and anti–B isoantibodies and type AB have neither.

Naturally occurring isoantibodies are virtually always directed against polysaccharide antigens. ABO isoantibodies are the most significant naturally occurring antibodies in clinical medicine. They are strongly reactive at physiologic temperature. An ABO transfusion mismatch can have fatal consequences, and the existence of these antibodies provides the fundamental reason for a strict blood typing before transfusion.

Naturally occurring isoantibodies directed against other red cell polysaccharide antigens also exist. Le in negative (le/le) individuals can possess antibodies against both Lea and Leb antigens. Anti–Lewis antibodies rarely cause significant hemolytic reactions, perhaps because the Lewis antigens will dissociate from the red cell more readily than the intrinsic antigens.

Naturally occurring isoantibodies of the MN system are usually cold–reacting complete agglutinins less commonly they are reactive at physiologic temperatures, transfusions reactions. Cold reacting anti–P₁ are found in P₂ individuals.

What stimulates the production of naturally occurring isoantibodies? By definition, a person possessing naturally occurring isoantibodies to a given red cell antigen has not been previously exposed to RBCS bearing antigen. The most popular explanation is that bacterial cell walls may have antigens in common with the red cell surface and that isoantibodies result from immune stimulation by these cross reacting bacterial antigens.

2. Isoantibodies arising from Immunization

Direct immunization with red cell antigens usually result either from mismatched transfusion leakage of fetal cells into the maternal circulation during pregnancy and delivery. These isoantibodies are predominantly IgG once the response has become establish.

3. Autoantibodies

Occasionally, individuals may make antibodies against their own red cell antigens. They can be responsible for a serious hemolytic anemia.