Transcript A antigen
BLOOD GROUP AND ABO ANTIGENS Lecturer Bahiya Osrah History: Karl Landsteiner • Discovered the ABO Blood Group System in 1901 • Blood types: • Type A, Type B, Type AB, & Type O The identification of blood group depends on the antigen and antibodies produced by the immune system. http://www.nobelpreis.org/castellano/medizin/images/landsteiner.jpg Introduction • Antigens: chemical structures imparting specific properties to the surface of the RBC • Antibodies: protein substance developed in response to foreign body substances • Three antigens we need to focus on: A, B, and H antigens that are usually expressed on the red blood cells surface. • The presence or absence of the A, B, and H antigens is controlled by the H and ABO genes ABO Basics • Blood group antigens are actually sugars attached to the red blood cell. • Antigens are “built” onto the red cell. • Individuals inherit a gene which codes for specific sugar(s) to be added to the red cell. • The type of sugar added determines the blood group. H Antigen • The H gene codes for an enzyme that adds the sugar fucose to the terminal sugar of a precursor substance (PS) • The precursor substance (proteins and lipids) is formed on an oligosaccharide chain (the basic structure) RBC Precursor Structure RBC Glucose Precursor Substance (stays the same) Galactose N-acetylglucosamine Galactose Formation of the H antigen RBC Glucose H antigen Galactose N-acetylglucosamine Galactose Fucose A and B Antigen • The “A” gene codes for an enzyme (transferase) that adds N-acetylgalactosamine to the terminal sugar of the H antigen • N-acetylgalactosaminyltransferase • The “B” gene codes for an enzyme that adds Dgalactose to the terminal sugar of the H antigen • D-galactosyltransferase Formation of the A antigen RBC Glucose Galactose N-acetylglucosamine Galactose Fucose N-acetylgalactosamine Formation of the B antigen RBC Glucose Galactose N-acetylglucosamine Galactose Fucose Galactose Genetics • The H antigen is found on the RBC when you have the Hh or HH genotype, but NOT from the hh genotype • The A antigen is found on the RBC when you have the Hh, HH, and A/A, A/O, or A/B genotypes • The B antigen is found on the RBC when you have the Hh, HH, and B/B, B/O, or A/B genotypes ABO Type Frequencies In U.S. ABO Type Per Cent O 45% A 40% B 11% AB 4% Landsteiner’s Rule • Individual’s will form immune antibodies to ABO blood group antigens they do not possess. • Critical for understanding compatibility between ABO blood groups. Antibody clinical significance • Immunizations are frequently done to protect us from disease. • Receive Hepatitis B immunization. • Actual bits of hepatitis virus injected. • Body recognizes as foreign and produces an immune antibody. • Subsequent exposure to real Hepatitis B virus will result in destruction of the virus by immune antibodies. • ABO antibodies are immune and will result in destroying incompatible cells which may result in the death of the recipient. Genetics • Two genes inherited, one from each parent. • Individual who is A or B may be homozygous or heterozygous for the antigen. • Heterozygous: AO or BO • Homozygous: AA or BB • Phenotype is the actual expression of the genotype, ie, group A • Genotype are the actual inherited genes which can only be determined by family studies, ie, AO. Group O • Approximately 45% of the population is group O. • Has NO antigens on RBC surface • Has anti-A & anti-B antibodies in the plasma • Universal Donor: can be given to any blood type no antigens on the RBCs • Genotype OO = Phenotype O Group A • Approximately 40% of the population is group A. • No B antigens present. • Has A antigens on the RBC surface • Has anti-B antibodies in the plasma • Genotypes AA & AO = Phenotype A Group B • Approximately 11% of the population is group B. • No A antigens present. • Has B antigens on the RBC surface • Has anti-A antibodies in the plasma • Genotype BB & BO = Phenotype B Group AB • Approximately 4% of the population is group AB. • Has A & B antigens on the RBC surface • Has NO antibodies in the plasma • Universal Recipient: can receive Type A, Type B, Type AB, or Type O blood NO antibodies in plasma to react with antigens • Genotypes: AB = Phenotype AB • NOTE: This slide is in error as it only illustrates presence of one antigen not 2. Hemolysis • If an individual is transfused with an incompatible blood group destruction of the red blood cells will occur. • This may result in the death of the recipient. Summary Blood Group Antigens on cell Antibodies in plasma Transfuse with group A A Anti-B A or O B B Anti-A B or O AB A and B none O None Anti-A & B AB, A, B or O O Rh (D) Antigen • Rh refers to the presence or absence of the D antigen on the red blood cell. • Discovered by Landsteiner & Wiener in 1937 • Discovered in the Rhesus monkey • Rh is an antigen on the RBC surface • Rh + has the antigens on the RBC (85% of population) • Rh – does NOT have the Rh antigens • Rh + can accept Rh + or Rh – blood • Rh – can accept ONLY Rh - blood Rh (D) Antigen • Production of antibody to D requires exposure to the antigen. • The D antigen is very immunogenic, ie, individuals exposed to it will very likely make an antibody to it. • For this reason all individuals are typed for D, if negative must receive Rh (D) negative blood. • Because the Rh(D) positive individuals already have D antigen and that will trigger the immune response of the negative individuals to the D-antigens and that will cause death •Erythroblastosis fetalis • Rh– mother and Rh+ father Rh+ child 1st pregnancy • during pregnancy fetal Rh pos rbc’s escape into maternal circulation (antigents) • Mother develops antibodies to baby’s Rh+ antigens • 2nd pregnancy with Rh+ child mother’s anti-Rh antibodies attack unborn child’s RBCs • Prevention: shot of Rhogam shortly after birth of first Rh+ baby to block development of antibodies • Antigen-antibody reaction due to mixing of Rh+ blood of fetus with Rh- blood of mother during 2nd Rh+ pregnancy Blood Typing • There are 2 components to blood typing: • Test unknown cells with known antibodies • Test unknown serum/plasma with known rbc’s • The patterns are compared and the blood group is determined. Slide Blood Typing - continued • The slide is divided into halves. • On one side a drop of anti-A is added, this will attach to and cause clumping of rbcs possessing the A antigen. • On the other side a drop of anti-B is added which will cause clumping of rbcs with the B antigen. • A drop of rbcs is added to each side and mixed well with the reagent. • The slide is tilted back and forth for one minute and observed for agglutination (clumping) of the rbcs Interpretation of Slide Typing Testing with Anti-A Anti-Serum • If an rbc contains the A antigen the red blood cells will be agglutinated by anti-A, a positive reaction. • If an rbc does not have the A antigen there will be no clumping, a negative reaction. Interpretation of Slide Typing Testing with Anti-B Anti-Serum • If an rbc contains the B antigen the red blood cells will be agglutinated by anti-B, a positive reaction. • If an rbc does not have the B antigen there will be no clumping by anti-B, a negative reaction. Slide Blood Typing Group A • An unknown rbc suspension is added to known anti-sera. • The left hand of the slide contains anti-A which reacts with the unknown cell. • The right hand side contains anti-B which does not react with the cell. Slide Blood Typing Group B • An unknown rbc suspension is added to known anti-sera. • The left hand of the slide contains anti-A does not react with the unknown cell. • The right hand side contains anti-B which reacts with the cell. Slide Blood Typing Group O • The left hand of the slide contains anti-A does not react with the unknown cell. • The right hand side contains anti-B does not react with the unknown cell. Slide Blood Typing Group AB • The left hand of the slide contains anti-A which reacts with the unknown cell. • The right hand side contains anti-B which reacts with the unknown cell. Summary of Slide Typing Anti-A Anti-B Blood Group NEG NEG O POS NEG A NEG POS B POS POS AB Any questions?? References • Cte.unt.edu/health/curriculum/blood_types.ppt • Cls.umc.edu/COURSE/CLS325/Week2/ABOsystem.ppt • www.austincc.edu/mlt/clin1/ABO.ppt