Other Red Cell Blood Group Systems

Core Learning Objectives and Systematic Evaluation

• Identify the major antigens within various blood group systems outside of ABO and Rh.

• List the frequencies of observed phenotypes and establish their associations with ethnic group diversity.

• Describe the biochemical characteristics of antigens within each distinct blood group system.

• Explain the genetic mechanisms underlying antigen expression for each system.

• Compare and contrast the serological characteristics and clinical relevance of associated antibodies.

• Identify unique system characteristics, including disease associations and specific biological functions.

• Evaluate systems based on the following diagnostic criteria:

  • Abbreviation for each antigen.

  • Clinical significance of the antibodies.

  • Immunoglobulin class ($IgG$ or $IgM$).

  • Optimal temperature of reaction in vitro.

  • Optimal reaction phase in vitro (e.g., IS, $37^{\circ}C$, AHG).

  • Response of the antigen to enzyme treatment.

Kell Blood Group System

• Overview and Similarities: The Kell system is often compared to the Rh system due to its complexity and the high immunogenicity of its antigens.

• Major Antigens:

  • K ($K1$): Found in less than $9\%$ of the population.

  • k ($K2$, also known as cellano): Observed in more than $90\%$ of the population.

  • Antithetical Relationship: K and k are antithetical alleles.

• Development and Immunogenicity:

  • Antigens are well-developed at birth.

  • The $K1$ antigen is the second most immunogenic antigen in blood banking, following the D antigen.

  • Statistics: $1$ in $10$ individuals who are $K-$ will produce anti-K if exposed to $K+$ blood. Approximately $1/3$ of all non-Rh antibodies encountered in the lab are anti-K.

• Other Kell Antigens (Rh Equivalents): Analogous to the Rh system's C/c and E/e pairs.

  • Kp series:

    • $Kp^a$: A low-frequency antigen (found in only $2\%$ of people).

    • $Kp^b$: A high-frequency antigen (found in $99.9\%$ of people).

  • Js series:

    • $Js^a$: Found in $20\%$ of Black individuals but only $0.1\%$ of Caucasians.

    • $Js^b$: A high-frequency antigen ranging from $80\%$ to $100\%$.

• Biochemistry and Treatment Responses:

  • Disulfide Bonds: Kell antigens possess disulfide-bonded regions on their glycoproteins.

  • Sulfhydryl Sensitivity: Because of these bonds, antigens are sensitive to sulfhydryl reagents which break the bonds:

    • $2$-mercaptoethanol ($2$-ME).

    • Dithiothreitol (DTT).

    • $2$-aminoethylisothiouronium bromide (AET).

  • Enzyme Resistance: Proteolytic enzymes do not affect Kell antigens.

• Genetics and Alleles:

  • Sets of alleles include: K/k, $Kp^a/Kp^b$, $Js^a/Js^b$, $KEL11/KEL17$ (also called $Wk^a$), and $KEL14/K24$.

  • High-incidence alleles: k, $Kp^b$, $Js^b$, and $KEL11$.

  • Low-incidence alleles: K, $Kp^a$, $Js^a$, and $KEL17$.

• The Null Phenotype ($K^0$):

  • Definition: Lacks all Kell system antigens ($K^0K^0$).

  • Expression: Expresses the related $Kx$ antigen.

  • Clinical Consequence: Following RBC stimulation, these individuals can develop anti-Ku (an antibody directed against the universal Kell substance). Anti-Ku is clinically significant and necessitates the use of rare donor blood.

• Kell Antibodies:

  • Class: $IgG$.

  • Stimulation: RBC stimulated via transfusion or pregnancy.

  • Laboratory Findings: Agglutinates best in the indirect antiglobulin test (IAT/AHG). They usually do not bind complement.

  • Clinical Impact: Strongly associated with Hemolytic Transfusion Reactions (HTRs) and Hemolytic Disease of the Fetus and Newborn (HDFN). Anti-K is the most common specificity.

Kx Blood Group System and McLeod Syndrome

• Kx Characteristics: The $Kx$ antigen is phenotypically related to the Kell system but is genetically distinct.

• X-Chromosome Inheritance: The system is inherited on the X chromosome, meaning defects are primarily seen in males.

• McLeod Phenotype: A lack of the $Kx$ antigen results in RBC abnormalities known as the McLeod phenotype.

• McLeod Syndrome: This clinical condition is the manifestation of the McLeod phenotype.

  • Symptoms: Muscular and neurological defects.

  • RBC Morphology: Acanthocytosis (star-shaped red cells).

  • Infection Risk: Increased susceptibility to infection.

  • Biomarkers: Increased levels of creatine kinase.

  • Chronic Granulomatous Disease (CGD): Often associated with CGD, where white blood cells can engulf pathogens but cannot kill them (impaired phagocytosis).

Duffy Blood Group System

• Antigen Characteristics:

  • Antigens: $Fy^a$ ($FY1$) and $Fy^b$ ($FY2$).

  • Expression: Well-developed at birth and detectable on fetal cells.

  • Alleles: Codominant alleles.

  • Stability: Antigens are destroyed by proteolytic enzymes and deteriorate during storage.

• Malaria Association:

  • Resistance: Most African Americans possess the $Fy(a-b-)$ phenotype.

  • Mechanism: $Fy^a$ or $Fy^b$ acts as a specific receptor for malarial merozoites ($Plasmodium\,knowlesi$ and $Plasmodium\,vivax$). Individuals lacking these antigens ($Fy(a-)$ and $Fy(b-)$) are resistant to infection by these parasites.

  • Evolution: The high frequency of $Fy(a-b-)$ in West and Central African populations suggests selective evolution against malaria.

• Duffy Antibodies:

  • Class: $IgG$.

  • Phase: React best at the AHG phase.

  • Clinical Impact: Clinically significant (HTRs and pregnancy-related stimulation); however, they are not a common cause of HDFN.

  • Complement: Usually do not bind complement.

  • Dosage: Antibodies often show dosage, reacting more strongly with homozygous cells ($Fy(a+b-)$ or $Fy(a-b+)$) than heterozygous cells ($Fy(a+b+)$).

  • Prevalence: Anti-$Fy^a$ is more frequently encountered than anti-$Fy^b$.

Kidd Blood Group System

• Antigen Details:

  • Major Antigens: $Jk^a$, $Jkb$, and $Jk3$.

  • Jk3 Presence: $Jk3$ is always present if $Jk^a$ and/or $Jk^b$ are inherited.

  • Phenotype Frequencies in the US:

    • Black population: Primarily $Jk(a+b-)$ at $51.1\%$.

    • Caucasian population: Primarily $Jk(a+b+)$ at $50.3\%$.

• Kidd Null Phenotype ($Jk(a-b-)$):

  • Most common in individuals from the Far East or Pacific Islands.

  • Resistance: RBCs are resistant to lysis in $2M$ urea.

  • Can produce the anti-$Jk3$ antibody.

• Kidd Antibodies:

  • Characteristics: $IgG$, clinically significant, and may bind complement.

  • Phase: Best detected at the AHG phase.

  • The Delayed HTR Hazard: Kidd antibodies are notorious as a common cause of delayed hemolytic transfusion reactions because their titers drop quickly below detectable levels.

  • Laboratory Optimization: Detection is aided by enzymes, Low-Ionic-Strength Solution (LISS), and Polyethylene Glycol (PEG).

  • Dosage: Shows dosage effects.

Lutheran Blood Group System

• Structure and Prevalence:

  • Total of $19$ antigens located on chromosome $19$.

  • Expression: Weakly expressed on cord blood cells.

  • Primary Antigens: $Lu^a$ and $Lu^b$.

  • Phenotype Frequencies:

    • $Lu(a-b+)$: $92.4\%$

    • $Lu(a+b+)$: $7.4\%$

    • $Lu(a+b-)$: $0.2\%$

  • Null Phenotype: The $Lu_{null}$ phenotype is rare and inherited recessively.

• Lutheran Antibodies:

  • Anti-$Lu^a$:

    • Class: $IgM$ and $IgG$.

    • Stimulation: May occur without RBC exposure.

    • Reaction: Best at room temperature.

    • Key Feature: Exhibits a mixed-field pattern of agglutination.

    • Not clinically significant.

  • Anti-$Lu^b$:

    • Class: $IgG$.

    • Antigen Context: Rare antibody because the antigen is high-frequency.

    • Reaction: Best at AHG.

    • Key Feature: Also exhibits a mixed-field pattern.

    • Clinically significant for transfusion reactions.

MNS Blood Group System

• Glycophorin A (GPA): Codes for the M and N antigens.

  • Structure: Sialoglycophorin A consisting of $131$ amino acids.

  • Differences: M and N differ at positions $1$ and $5$ of the GPA chain.

  • Proximity: Located on the outer end of the GPA; easily destroyed by enzymes.

  • Dosage: Agglutination is enhanced by homozygous inheritance ($M+N-$) or ($M-N+$).

• Glycophorin B (GPB): Codes for the S, s, and U antigens.

  • Structure: Sialoglycophorin B consisting of $72$ amino acids.

  • Differences: S and s differ at position $29$ (S has methionine; s has threonine).

  • U Antigen: Located near the RBC membrane; present when S or s is inherited. Absence of GPB leads to the $S-s-U-$ phenotype.

  • Ethnic Specificity: $U-$ individuals are only found in the Black population (less than $1\%$).

• Antibody Characteristics in MNS:

  • Anti-M:

    • Class: Usually $IgM$ ($50-80\%$ may have an $IgG$ component).

    • Reaction: Best at room temperature or colder; agglutination seen at IS, $37^{\circ}C$, or AHG.

    • Enzyme sensitivity: Destroyed by enzymes.

    • Clinical Significance: Only significant if reactive at $37^{\circ}C$ or AHG.

  • Anti-N:

    • Class: Cold-reactive $IgM$.

    • Dialysis Association: N-like antibodies are found in dialysis patients due to formaldehyde-sterilized instruments.

  • Anti-S, Anti-s, and Anti-U:

    • Class: Clinically significant $IgG$.

    • Reaction: Best at $37^{\circ}C$ and AHG.

    • Can cause HDFN and HTR.

Lewis Blood Group System

• Origin of Antigens: Unlike other systems, Lewis antigens are not intrinsic to the RBC membrane. They are found as glycoproteins in secretions and glycolipids in plasma.

• Adsorption: The glycolipids in plasma adsorb onto the RBC membrane surface.

• Genetics: Depends on the interaction of $Hh$, $Se$, and $Le$ genes.

  • If $Le$ is inherited: $Le^a$ substance is produced.

  • If $Le$, $H$, and $Se$ are all inherited: $Le^a$ is converted to $Le^b$.

• Phenotypes and Pregnancy:

  • $Le(a+b+)$ is extremely rare in adults.

  • Antigens are significantly reduced during pregnancy; women may develop temporary "pseudo anti-Lewis" antibodies.

• Lewis Antibodies:

  • Class: $IgM$.

  • Producers: Usually produced by individuals with the $Le(a-b-)$ phenotype.

  • Anti-$Le^a$: Can bind complement and cause in vitro hemolysis.

  • Neutralization: Lewis antibodies can be neutralized by Lewis substance to help identify other underlying antibodies.

I Blood Group System

• I and i Relationship: These are reciprocal antigens, not antithetical.

• Developmental Switch: Newborns have linear $i$ antigen on cord cells. Over approximately $2$ years, $i$ converts to branched $I$ antigen as the child matures.

• Autoanti-I: A commonly encountered cold autoantibody (reacts optimally at $RT$ or below).

  • Avoidance: Interference is avoided by the prewarming technique.

• Compound Antibodies: Anti-IH is often found; it reacts more strongly with RBCs that have many H sites (Type O and $A_2$ cells).

• Disease Associations:

  • Autoanti-I: Strongly associated with $Mycoplasma\,pneumoniae$ and Cold Hemagglutinin Disease.

  • Anti-i: Associated with Infectious Mononucleosis, lymphoproliferative diseases, and occasionally Cold Hemagglutinin Disease.

P1PK and Globoside Blood Group Systems

• Antigen Localization:

  • $P_1$ antigen is present in plasma and hydatid cyst fluid.

  • Globoside system includes the P antigen.

• Antibodies:

  • Anti-$P_1$: An $IgM$ alloantibody found in $P_2$ individuals; neutralizable by $P_1$ substance.

  • Autoanti-P (Donath-Landsteiner antibody):

    • Class: $IgG$.

    • Condition: Associated with Paroxysmal Cold Hemoglobinuria (PCH).

    • Mechanism: A biphasic hemolysin that binds at low temperatures and activates complement upon warming.

  • Anti-$PP_1P^k$: Found in null phenotype individuals; causes in vitro hemolysis and is clinically significant.

Miscellaneous Blood Group Systems

HLA and Platelet Systems

• Human Leukocyte Antigens (HLA):

  • Located on leukocytes and tissue cells.

  • MHC Classes:

    • Class I: Found on platelets, leukocytes, and all nucleated cells.

    • Class II: Found on macrophages, dendritic cells, and B cells.

    • Class III: Code for complement and cytokines.

  • Inheritance: Inherited as haplotypes (one from each parent); codominant expression.

  • Testing: Lymphocytotoxicity test method (uses complement and dye).

  • Clinical Significance: Refractoriness to platelets, organ/HPC transplant matching, and disease susceptibility assessment.

• Platelet Antigens:

  • NAIT (Neonatal Alloimmune Thrombocytopenia): Maternal antibodies destroy newborn platelets.

  • PTP (Posttransfusion Purpura): Platelet destruction following transfusion.

  • HPA-1a ($Pl^{A1}$): The most common target for platelet antibodies; present in $98\%$ of the population.