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Abo system
- 1. ABO blood groupsystem Dr R Amita Assistant Professor Dept of Transfusion Medicine
- 2. Discovery • Karl Landsteiner(1900)discovered human A,B,O groups. • Von Decastello and Sturli (1902) discovered AB blood group. • Von Dungern and Hirszfeld(1911) divided group A into 2 subgroups A1 and A2. ABO system is classified into 6 groups: A1, A2, A1B, A2B, B, AB and O
- 3. Landsteiner’s law • 1.Ifan agglutinogen is present on red blood cell membrane ,the corresponding agglutinin must be absent in the plasma. • 2.If an agglutinogen is absent on red blood cell membrane, then corresponding agglutinin must be present in the plasma.
- 5. Antigens • Appear inthe sixth week of fetal life. • Present on red cell membrane, WBC, platelets and in other tissues like salivary glands, pancreas, kidney, body fluids • Exception CNS
- 6. ABO gene • TheABO blood type is controlled by a single gene (the ABO gene) with three types of alleles i, IA, and IB. • The gene encodes a glycosyltransferase • The gene is located on the long arm of the ninth chromosome (9q34). • IA allele gives type A, IB gives type B, i gives type O. • Co dominant • O group : Only ii AB group : IAIB • A group : IAIA or IAi B group : IBIB or IBi
- 7. Genetics • Inheritance ofgenes follows Mendelian Law • Bernstein theory: there is one locus on a chromosome at which any of the three alleles may be located
- 8. ABO Antigen Genetics •The presence or absence of the ABH antigens on the red blood cell membrane is controlled by the H gene (chr 19) • The presence or absence of the ABH antigens in secretions is indirectly controlled by the Se gene (chr 19) • H gene – H and h alleles (h is an amorph) • Se gene – Se and se alleles (se is an amorph) • ABO genes – A, B and O alleles
- 9. Biochemistry • Precursor: Paragloboside/Glycan •Type I precursor : terminal galactose linked to a subterminal N-acetylgluosamine in a 1-3 linkage. • Type II precursor : same sugars combine in a 1-4 linkage • ABH antigens on RBC are derived from Type II chains • Blood group substances in secretion are made from both types I & II precursors
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- 11. H substance • Hgene (FUT1 gene) leads to production of an enzyme α-2-L-Fucosyl transferase, which transfers fucose to the terminal galactose of the precursor Glucose Galactose N-acetylglucosamine Galactose RBC Fucose
- 12. A antigen • The“A” gene codes for N-acetylgalactosaminyltransferase that adds N-acetylgalactosamine to the terminal sugar of the H antigen Glucose Galactose N-acetylglucosamine Galactose RBC Fucose N-acetylgalactosamine
- 13. B antigen • The“B” gene codes for D-galactosyltransferase that adds D-galactose to the terminal sugar of the H antigen Glucose Galactose N-acetylglucosamine Galactose RBC Fucose Galactose
- 14. ABO Subgroups • ABOsubgroups differ in the amount of antigen present on the red blood cell membrane • Subgroups have fewer antigens are present on the RBC • Subgroups are the result of less effective enzymes (not as efficient in converting H antigens to A or B antigens) • Subgroups of A are more common than subgroups of B
- 15. Subgroups of A •A1 and A2 • Both react strongly with reagent anti-A • To distinguish A1 from A2 red cells, the lectin Dolichos biflorus is used (anti-A1) • 80% of group A or AB individuals are subgroup A1 • 20% are A2 or A2B
- 16. A2 Phenotype • TheA2 gene doesn’t convert the H3 & H4 to A very well • The result is fewer A2 antigen sites compared to the many A1 antigen sites. • A2 and A2B individuals may produce an anti-A1 • This may cause discrepancies when a crossmatch is done.
- 17. A1 and A2Subgroups Anti-A antisera Anti-A1 antisera Anti-H lectin ABO antibodies in serum # of antigen sites per RBC A1 4+ 4+ 0 Anti-B 900 x103 A2 4+ 0 3+ Anti-B & anti-A1 250 x103
- 18. Other A subgroups •There are other additional subgroups of A • Aint (intermediate), A3, Ax, Am, Aend, Ael, Abantu • A3 red cells cause mixed field agglutination when polyclonal anti-A or anti-A,B is used • Mixed field agglutination appears as small agglutinates with a background of unagglutinated RBCs • They may contain anti-A1
- 21. B Subgroups • Bsubgroups occur less than A subgroups • B subgroups are differentiated by the type of reaction with anti-B, anti-A,B, and anti-H • B3, Bx, Bm, and Bel
- 22. Other ABO conditions •Bombay Phenotype (Oh) • Inheritance of hh • Missense mutation of FUT1 gene • The h gene is an amorph and results in little or no production of L fucosyltransferase • Originally found in Bombay (now Mumbai) by Bhende in 1952 • Very rare (Frequency in India 1:10000)
- 23. Bombay group • Thehh causes NO H antigen to be produced • Results in RBCs with no H, A, or B antigen (Cell group: O) • Bombay RBCs are NOT agglutinated with anti-A, anti-B, or anti-H (no antigens present) • Bombay serum has strong anti-A, anti-B and anti-H, agglutinating ALL ABO blood groups. • Group O RBCs cannot be given because they still have the H antigen • Transfuse the patient with blood that contains NO H antigen
- 24. Parabombay phenotype • Hantigen is weakly expressed on RBCs. Weak expression of A, B, H antigens on the red cells (Due to passive adsorption from secretion) which react weakly with antisera to A, B, H antigens • H antigen is present in the secretions, but there is no expression on red cells. Serum contains anti-H antibodies • Genotype:hh/Sese or hh/SeSe
- 26. ABO Antigens inSecretions • Secretions include body fluids like plasma, saliva, synovial fluid, etc • Blood Group Substances are soluble antigens (A, B, and H) that can be found in the secretions. • This is controlled by the H and Se genes • Se gene (FUT2gene) encodes α2 L fucosyltransferase which modifies type 1 precursor to H substance • If the Se allele is inherited as SeSe or Sese, the person is called a “secretor” • 80% of the population are secretors
- 27. Secretor Status • TheSe gene codes for the presence of the H antigen in secretions, therefore the presence of A and/or B antigens in the secretions is contingent on the inheritance of the Se gene and the H gene Se gene (SeSe or Sese) H antigen in secretions A antigen B antigen se gene (sese) No antigens secreted in saliva or other body fluids and/or
- 28. ABO Group ABH Substances Secretors (SeSeor Sese): A B H A +++ 0 + B 0 +++ + O 0 0 +++ AB +++ +++ + Non-secretors (sese): A, B, O, and AB 0 0 0 Sese + h/h (no H antigen) no antigens in secretions
- 29. H antigen • Certainblood types possess more H antigen than others: • The O gene is a silent allele. It does not alter the structure of the H substance….that means more H antigen sites O>A2>B>A2B>A1>A1B Greatest amount of H Least amount of H
- 30. Group O GroupA Many H antigen sites Most of the H antigen sites in a Group A individual have been converted to the A antigen Fewer H antigen sites A A A AA Group O Group A
- 31. ABO antibodies • Naturalantibodies: does NOT require the presence of a foreign red blood cell for the production of ABO antibodies. • ABO antibodies are “non-red blood cell stimulated” probably from environmental exposure. • Titer of ABO Abs is often reduced in elderly and in patients with hypogammaglobulinemia and infants (until 3 -6 months of age)
- 32. ABO antibodies • IgMis the predominant antibody in Group A and Group B individuals • Anti-A • Anti-B • IgG (with some IgM) is the predominant antibody in Group O individuals • Anti-A,B (with some anti-A and anti-B)
- 33. Anti-A • Group Oand B individuals contain anti-A in their serum • However, the anti-A can be separated into different components: anti-A and anti-A1 • Anti-A1 only agglutinates the A1 antigen, not the A2 antigen • Occurs in 1-8% of A2 and 22-30% of A2B • There is no anti-A2.
- 34. Anti-A,B • Found inthe serum of group O individuals • Reacts with A, B, and AB cells • Predominately IgG, with small portions being IgM • Anti-A,B is one antibody, it is not a mixture of anti-A and anti-B antibodies
- 35. Anti H antibody •A1 gene very efficiently converts all of H substance to A antigen, • Therefore some A1 and A1B individuals may have anti H • IgM cold agglutinin • Best reacts at room temperature
- 36. Anti-H Auto-Anti-H Clinically Significant No Abs class IgM Thermal range 4- 15 HDNB No Transfusion Reactions Extravascular Intravascular No yes Allo-Anti-H (Bombay group) Clinically Significant Yes Abs class IgM, IgG Thermal range 4 - 37 HDNB Yes Transfusion Reactions Extravascular Intravascular Yes Yes
- 37. Frequency of bloodgroup system RBC Phenotype Frequency (%) Serum Ab A 24 Anti-B B 30 Anti-A AB 6 -------- O 40 Anti-A,B
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- 39. ABO discrepancies • GroupI Discrepancies - • These are associated with unexpected reactions in the reverse grouping due to weakly reacting or missing antibodies. • Includes: • Infants less than 4-6 month of age • Elderly patients • Severe hypogammaglobulinemia • ABO incompatible HPC transplantation
- 40. • Resolution: • Enhancingweak or missing reaction by incubating the patient’s serum with reagent A1 and B cells at room temperature for 15-30 minutes • Serum cell mixture is incubated at 4⁰C for 15-30 minutes • An autocontrol and O cell control must always be tested concurrently to detect reactivity of other commonly occurring cold agglutinins eg: anti I
- 41. • Group IIdiscrepancies • These are associated with unexpected reactions in forward grouping due to weakly reacting or missing antigen • Includes: • Weak subgroups of A or B • Weakening of A or B antigen in malignancies • Acquired B phenotypes: • results from the action of bacterial deacetylase, which converts N- acetylgalactosamine to ẞ-galactosamine, which is very similar to galactose, the chief determinant of B. • ‘passenger antigen’ type is caused by adsorption of B-like bacterial products on to O or A cells but occurs only in vitro. • Out of group transfusion or ABO mismatched HPSCT • Neutralization of anti A and anti B typing reagent by high concentration of A or B soluble substances in serum with serum or plasma suspended red cell
- 42. • Resolution ofgroup II discrepancies • Weaker reactions with antisera can be resolved by enhancing reaction of antigen with respective antisera by incubating test mixture at room temperature for 15-30 minutes • Sub groups causing group discrepancies can be resolved by adsorption elution studies • Acquired B phenomenon can be resolved by lowering PH of monoclonal antisera. Anti B in the serum of acquired B person does not agglutinate autologous red cells (autocontrol negative). • Secretor status of person can resolve acquired B, saliva of acquired B person contains A substance not B substance. • High concentration of A or B substance causing group discrepancies can be resolved by saline washing of red cells
- 43. • Group IIIdiscrepancies • These are associated with protein or plasma abnormalities, rouleaux formation and pseudoagglutination. • Includes • Elevated level of globulin from e.g. multiple myeloma, waldenstorm macroglobulinemia, Hodgkin lymphoma. • Elevated level of fibrinogen. • Small fibrin clot in plasma or incompletely clotted serum can be mistaken for red cell agglutinates in reverse grouping. • Sample with abnormal concentration of serum proteins, altered serum protein ratio, or high molecular weight volume expanders can aggregate reagent red cells and can mimic agglutination. • Rouleaux will disperse when suspended in saline. True agglutination is stable in the presence of saline
- 44. • Group IVdiscrepancies are due to miscellaneous problems. • Recent transfusion of out of group plasma containing component. • Cold alloantibodies (e.g. anti M) or autoantibodies (e.g. anti I), pH dependent autoantibodies, a reagent dependent antibody (e.g. EDTA, paraben) leading to unexpected positive eaction. • Recent infusion of IvIg which can contain ABO isoagglutinins. • Mixed field agglutination with circulating red cell of more than one ABO type.
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