Blood Group Systems and Antigens

Comprehensive vocabulary flashcards covering the biochemistry, genetics, clinical significance, and laboratory characteristics of major human blood group systems.

Rh System Immunogenicity Order

The relative immunogenicity ranking of the five major Rh antigens from greatest to least: $D > c > E > C > e$.

f Compound Antigen

A compound Rh antigen expressed when both $c$ and $e$ are present on the same haplotype, such as in $Dce$ ($R_0$) or $ce$ ($r$).

G Antigen

An antigen present on all red blood cells that express either the $D$ antigen or the $C$ antigen, found on all Rh-positive cells as well as $CE$ ($r^y$) and $Ce$ ($R_1$).

Rh null

A rare phenotype in which red blood cells express no Rh antigens; individuals produce anti-Rh29 that reacts with all Rh antigens and exhibit stomatocytes and mild anemia.

$D--$ Phenotype

A deleted Rh phenotype missing the RhCE protein, demonstrating the highest expression of the $D$ antigen and the ability to produce anti-Rh17 directed against CcEe antigens.

RHIG (RHOGAM)

Donor-derived anti-D administered to D-negative pregnant women at $26\text{ to }28\text{ weeks}$ of gestation to bind fetal D-positive antigens entering maternal circulation and prevent maternal alloimmunization.

KEL Gene

A gene located on chromosome $7$ encoding the high-frequency antigens $k$, $Kp^b$, and $Js^b$, which can mutate via single point mutations into the low-frequency antithetical antigens $K$, $Kp^a$, $Kp^c$, and $Js^a$.

McLeod Syndrome

An X-linked condition in males caused by the lack of the Xk protein, leading to the absence of the $Kx$ and $Km$ antigens and the presence of acanthocytosis.

K null (Kell Null)

A red blood cell phenotype characterized by the complete absence of the Kell glycoprotein, which results in increased expression of the $Kx$ antigen and the potential to produce anti-Ku.

Kidd Blood Group System

A blood group system located on chromosome $18$ functioning as a red blood cell urea transporter; its IgG antibodies show dosage, bind complement to cause intravascular hemolysis, cause delayed hemolytic transfusion reactions, and frequently fade in vivo to low titers.

Jk3 Phenotype

The null Kidd phenotype ($Jk(a-b-)$) commonly observed in Polynesian populations, in which individuals can produce anti-Jk3.

Duffy Blood Group System

A blood group system located on chromosome $1$ that functions as a chemokine receptor and provides the cellular receptor exploited by $Plasmodium\ vivax$ to invade red blood cells.

GATA Box Mutation

A genetic mutation common in individuals of African ancestry that silences the $FY$ gene specifically in erythroid tissue, rendering red blood cells $Fy(a-b-)$ to prevent $Plasmodium\ vivax$ infection while permitting anti-Fya (but not anti-Fyb) production.

Glycophorin A (GPA)

A transmembrane protein encoded on chromosome $4$ that carries the $M$ and $N$ antigens, which are distinguished by single point mutations.

Anti-Nf

An antibody against the $N$ antigen that develops secondary to formaldehyde exposure, commonly found in patients undergoing kidney dialysis.

En(a) Antigen

A high-prevalence red blood cell envelope structure located on RBC with M or N

Absent in individuals are due to complete Glycophorin A gene deletion ($M-N-$ ).

• can make anti-En(a); unexpected antibody

Glycophorin B (GPB)

A red blood cell protein that carries the $S$ and $s$ antigens as well as an 'N-like' sequence, reducing the likelihood of anti-N production in $MM$ individuals unless GPB is deleted.

U Antigen

high prevalance, present if S and s antigens are present

U null (= S=s=) are exclusively found in African population

• Anti-U (unexpected) can cause HTR and HDFN

$M^k$ Gene

A rare null allele causing the complete deletion of both Glycophorin A and Glycophorin B, resulting in an $M-N-S-s-$ phenotype capable of producing anti-M, anti-N, anti-S, anti-s, anti-U, and anti-En(a).

MUR Antigen

A mutation on Glycophorin B commonly identified in Southeast Asian populations that is highly immunogenic and can cause hemolytic transfusion reactions and HDFN.

Lewis Antigens

Soluble antigens produced by tissue cells and secreted into body fluids that passively adsorb onto red blood cell membranes rather than being synthesized directly on the erythroid cell.

FUT3 (Le Gene)

Le (FUT3) add fucose on Type 1 chain (β-1,3 linkage) → Le(a) (this is b=)

FUT2 (Se Gene)

Se (FUT2) add fucose on Type 1 chain → form H type 1 chain → Le (FUT3) add another fucose onto H type 1 chain → Le(b) (this is a=)

$P^k$ Antigen (Gb3)

A globoside glycolipid intermediate formed from lactosylceramide (Gb2) that serves as the biological receptor for Shiga toxin and $Escherichia\ coli$.

Anti-P1

A naturally occurring IgM antibody directed against the $P_1$ antigen that is associated with pigeon exposure and can be neutralized in vitro by $P_1$ substance.

Auto-anti-P

A biphasic IgG autoantibody (Donath–Landsteiner antibody) that binds red blood cells at cold temperatures and causes intravascular complement hemolysis upon warming; associated with paroxysmal cold hemoglobinuria (PCH) and tertiary syphilis.

Anti-PP1Pk (Anti-Tja)

A complex antibody produced by individuals with the null $p$ phenotype that reacts against $P$, $P_1$, and $P^k$ antigens; notable for causing severe spontaneous abortions and found in consanguineous Amish populations.

I Antigen

A branched carbohydrate structure formed from linear $i$ chains as infants mature, becoming fully expressed on adult red blood cells past $18\text{ months}$ of age.

Cold Agglutinin Disease (CAD)

A clinical condition involving high-titer auto-anti-I reacting at warmer temperatures of $30\text{ to }32\,^\circ\text{C}$, frequently triggered by $Mycoplasma\ pneumoniae$ infection.

Anti-IH

A cold-reactive antibody that targets a compound epitope formed by $I$ and $H$ antigens, typically emerging in group $A_1$ individuals due to their low expression of H antigen.

In(Lu)

A dominant inhibitor gene that suppresses or weakens the phenotypic expression of all Lutheran system antigens, including $Lu^a$ and $Lu^b$.

common in Japanese

Diego Blood Group System

A red blood cell system located on the anion exchanger membrane protein consisting of the low-frequency antigen $Di^a$ (prevalent in Native American and Mongolian populations) and the high-frequency antigen $Di^b$.

Chido/Rogers (Ch/Rg) Antigens

High-titer, low-avidity (HTLA) antigens composed of complement C4 fragments adsorbed onto red blood cells that can be neutralized by human plasma.

Bennett-Goodspeed (Bg) Antigens

High-titer, low-avidity antigens related to HLA molecules present on red blood cells that can be neutralized by chloroquine.

DTT Sensitivity of Kell

The destruction of Kell system antigens by the reducing chemical dithiothreitol (DTT), which disrupts the disulfide bond linking the Kell glycoprotein to the Xk protein.

Proteolytic Enzyme-Destroyed Antigens

Antigens whose protein structures are cleaved and inactivated upon exposure to proteolytic enzymes, specifically MNSs, Duffy ($Fy^a/Fy^b$), and $Xg^a$.

Proteolytic Enzyme-Enhanced Antigens

Antigens whose serological reactivity increases after treatment with proteolytic enzymes, including ABO, Rh, Kidd, I, Lewis, and P.