Recap of ABO and Carbohydrate Blood Group Systems

• Overview: This lecture is a recap of carbohydrate antigens in blood group systems, designed to summarize key information and highlight points important for the ASCP exam. For in-depth understanding, refer to individual lectures on each topic.

1. Carbohydrate Antigens: General Characteristics

• Not Direct Gene Products: Carbohydrate antigens are not directly produced by genes.

  • Genes produce transferases, which are enzymes.

  • Transferases catalyze the production of antigens.

  • This is done by adding specific sugars to existing carbohydrate chains.

• Common Precursor Structure: All carbohydrate antigens share a common precursor structure.

  • This precursor is a lactosylceramide, which serves as the building block.

  • There are two types of precursor substances:

    • Type 1 Precursor: Predominantly found in body fluids and secretions.

    • Type 2 Precursor: Primarily located on red blood cells (RBCs).

• Image Reference: The provided image is helpful as it illustrates how different carbohydrate antigens branch out from a common precursor structure.

2. ABO Blood Group System

• Most Important System: ABO is the most critical blood group system in transfusion and transplant medicine.

  • This is due to the presence of naturally occurring antibodies against ABO antigens.

• Genes Involved: Three genes are responsible for ABO antigens:

  • ABO gene

  • H gene

  • Secretor gene

• Antigen Development:

  • ABO antigens are detectable in utero as early as 5-6 weeks of gestation.

  • They reach full adult strength around 2-4 years of age.

• H Antigen Expression: Memorize the H antigen expression chart (though not explicitly shown in the transcript, it’s referenced as important).

  • O cells: Have the most H antigen expression.

    • React strongest with anti-H.

  • (Implied: A and B blood types have less H antigen, and AB has the least).

• ABO Antibodies:

  • Predominantly IgM.

  • Naturally occurring.

  • Anti-A and anti-B are not present at birth.

    • Reason why reverse typing is not performed on newborns or cord blood.

  • Antibodies normally appear around 3 months to 1 year of age.

  • Reach full adult titers between 5 to 10 years of age.

• ASCP Exam Relevance: For the ASCP exam, you need to understand:

  • Basic biochemistry of the ABO system.

  • How to resolve ABO discrepancies.

  • The relationship between secretor, ABO, and Lewis antigens.

3. Lewis Blood Group System (ISBT 007)

• Unique Antigen Location: Lewis antigens are not intrinsic to RBCs.

  • They are synthesized on Type 1 precursor substances found in secretions.

  • Then, they are absorbed onto the RBC membrane from the plasma.

• Primary Lewis Antigens: The two main Lewis antigens are:

  • Lewis a (Le^a)

  • Lewis b (Le^b)

• Lewis Locus Alleles: Two alleles exist at the Lewis locus:

  • LE (capital LE)

  • le (lowercase le)

  • The le allele is an amorph, meaning it does not produce a functional transferase and thus no Lewis antigen directly.

• Secretor Locus Alleles: Similar to Lewis, the secretor locus has two alleles:

  • SE (capital SE)

  • se (lowercase se)

  • The se allele is also an amorph, not producing a functional secretor transferase.

• Synthesis Dependence: Lewis antigen synthesis depends on two genes (fucosyltransferases):

  • FUT2 (Fucosyltransferase 2): This is the secretor gene.

  • FUT3 (Fucosyltransferase 3): This is the Lewis gene.

• Image Explanation (Lewis and Secretor Interaction): The provided image is crucial for understanding Lewis antigen expression based on the presence or absence of Lewis and secretor genes.

  • Lewis negative and secretor negative (lele sese):

    • No Lewis antigens (Le(a-b-)).

    • No H antigens in secretions.

  • Lewis positive and non-secretor (LEle sese or LELE sese):

    • Lewis a (Le^a) present (Le(a+b-)).

  • Lewis positive and secretor positive (LEle SEse, LELE SEse, LEle SESE, LELE SESE):

    • Lewis b (Le^b) present (Le(a-b+)).

• FUT Gene Functions:

  • FUT1 (Fucosyltransferase 1): Makes H antigen on RBCs.

    • Adds fucose to Type 2 precursor substances.

  • FUT2 (Secretor gene): Adds fucose to Type 1 precursor substance in secretions.

  • FUT3 (Lewis gene): Adds fucose to Type 1 precursor substance also in secretions.

• Interaction of Lewis and Secretor Genes:

  • Lewis without Secretor (LE and sese): Only Lewis a (Le^a) activity is seen.

  • Both Lewis and Secretor (LE and SE): Presence of Lewis b (Le^b).

    • A small amount of Lewis a may still be present in secretions, but Lewis b is the predominant antigen.

  • Neither Secretor nor Lewis (lele sese): Lewis A and B negative (Le(a-b-)).

• Lewis Antibodies:

  • Made by Lewis a and b negative individuals (Le(a-b-)).

  • Often produce both anti-Le^a and anti-Le^b.

  • Optimal reaction at room temperature (RT), but can also react at 37°C.

  • Usually IgM, but sometimes IgG.

  • Rarely cause transfusion reactions, generally considered “annoying” antibodies.

  • Can be neutralized with Lewis substance.

  • Anti-Le^a is common in pregnant women.

  • Most are naturally occurring.

  • Enzyme-treated cells enhance reactivity.

• Clinical Significance & Management of Lewis Antibodies:

  • Usually not clinically significant.

  • Give Cross Match compatible blood.

  • Pre-warm technique can be used to avoid interference in testing.

4. I Antigens

• Link to ABO and H: I antigens are closely linked to ABO and H antigens.

• Cold Reactive Antibodies: The type of cold reactive antibody produced is related to ABO blood type.

  • Linked to the expression of A, B, H, and I antigens on the RBC surface.

• Structure:

  • Little i antigen: Linear precursor structure.

  • Big I antigen: Branched structure of the little i antigen.

• H and I Antigen Expression Chart (Implied): Chart shows the relative amounts of H and I antigens on different blood types. (Not shown but referred to).

• Mini Cold Panel: Used to identify cold reacting antibody specificity.

  • Typically involves cord cells (rich in little i, poor in Big I) and reagent cells (adult cells, rich in Big I, less little i).

• Resolving Typing Issues with Cold Antibodies: Cold antibodies can cause problems with blood typing.

  • Example: Forward type A, Reverse type O. A cold autoantibody can cause extra reactions in reverse typing.

  • Resolution method: Use pre-warm technique for antibody screen and typing reagents.

    • Pre-warm all screen reagents; screen should become negative.

    • Pre-warm reverse typing reagent cells.

    • Pre-warm patient plasma for reverse typing.

    • This should allow the reverse type to correctly identify as Type A.

• Clinical Significance & Management of I Antibodies:

  • Usually not clinically significant, mainly “annoying.”

  • For transfusion, a blood warmer might be used.

5. P1PK and Globoside Blood Group Systems

• P1PK Blood Group System (ISBT 003):

  • Three antigens: P1, P^K, and p.

• Globoside Blood Group System:

  • Two antigens: P and P^X2.

• LU Blood Group: Antigen Luke was initially in Globoside but moved to the high prevalence 901 series.

• Structure Chart (Optional): Chart visualizing the structures can be helpful for understanding relationships (not essential to memorize for exam, but aids understanding).

• Phenotypes – Clinical Significance:

  • Little p phenotype is the most clinically significant.

    • Individuals with this phenotype can make a clinically significant anti-P antibody.

• Phenotype Chart (Key to Understand Phenotypes):

  • P1 phenotype: Antigens present: P, P1, P^K. Antibodies made: None.

  • P2 phenotype: Antigens present: P, P^K. Antibodies made: Anti-P1.

  • P1^K phenotype: Antigens present: P1, P^K. Antibodies made: Anti-P.

  • P2^K phenotype: Antigens present: P^K. Antibodies made: Anti-P and anti-P1.

  • Little p phenotype: Antigens present: None (no P1, P^K, or P). Antibodies made: Anti-P, anti-P1, anti-P^K (all antibodies of the system).

• P1 Phenotype & Anti-P^K: P1 phenotype cells have P^K but usually don’t react with anti-P^K because P1 antigen may sterically hinder or mask P^K.

• Antibodies Related to P Systems:

  • Allo Anti-P:

    • Rare antibody because P antigen frequency is very high (>99.9%).

    • Transfusion reactions are rare (incompatible Cross Match would prevent transfusion).

    • HDN (Hemolytic Disease of the Fetus and Newborn) is unlikely.

    • Known to cause spontaneous abortions in Little p mothers.

  • Auto Anti-P:

    • Cause of Paroxysmal Cold Hemoglobinuria (PCH).

    • Powerful biphasic IgG hemolysin.

    • Donath-Landsteiner Test: Test for PCH.

      • Incubate cells at 4°C (cold phase), then warm to 37°C (warm phase).

      • Positive test: Hemolysis occurs (due to biphasic nature of auto-anti-P).

    • Don’t confuse PCH with PNH (Paroxysmal Nocturnal Hemoglobinuria).

    • More common in children than adults.

  • Anti-P1:

    • Found in P2 individuals.

    • Almost always naturally occurring IgM antibody.

    • Reacts best colder than room temperature.

    • Rarely binds complement.

    • Can be neutralized.

    • Does not cause HDN.

    • Manage by giving Cross Match compatible units.

  • Anti-P P1 P^K:

    • Naturally occurring antibody in Little p individuals.

    • Does not require stimulation to produce.

    • Reacts at RT, 37°C, and AHG phase.

    • Potent hemolysin.

    • Can cause spontaneous abortions and severe transfusion reactions.

Summary & Further Learning:

• This was a quick recap of carbohydrate blood group systems.

• Refer to individual lectures for a deeper understanding of each system.