transfusion red cell antigens part 1 of 1 week 19.pptx

Red Cell Antigens & Blood Types Geoff White Transfusion Science 1 1 Session Aims and Outcomes this session aims for you to gain an understanding of : Red Cell Antigens & Antibodies Structure and Function of Blood Group Antigens ABO, Rh & Other Blood Group Antigens Blood Phenotyping By the end of...

Red Cell Antigens & Blood Types Geoff White Transfusion Science 1 1 Session Aims and Outcomes this session aims for you to gain an understanding of : Red Cell Antigens & Antibodies Structure and Function of Blood Group Antigens ABO, Rh & Other Blood Group Antigens Blood Phenotyping By the end of this session you should be able to explain How the immune system creates antibodies to blood group antigens Why blood group antigens are needed for red cell function Why blood phenotyping is important in blood bank practice. Transfusion Science 2 The Red Cell Membrane  Red Cell Membrane showing Glycocalyx, Lipid Bilayer & Cytoskeleton (from Issitt & Anstee,1999) Transfusion Science 3 Red Cell Antigens Defn. an Immunogen is anything which stimulates a specific immune response an Antigen is a substance capable of eliciting an immune response and reacting specifically with the product of that response normal humoral response to a foreign Antigen is production of an antibody  an Antigen may be comprised of several different epitopes an immune response will produce a number of Antibodies that bind specifically to each particular epitope on an Antigen Transfusion Science 4 Red Cell Antigens Defn. Immunogenicity is a measure of the ability of an antigen to provoke an immune response this is dependent on number of features of the antigen  includes degree of polymorphism, molecular characteristics, accessibility & number of copies an Immunogenic Antigen is more likely to induce an immune response white blood cell groups are generally immunogenic many red cell blood groups are not very immunogenic Transfusion Science  5 Immune Response may produce Red Cell Antibodies exposure to ‘foreign’ immunogenic Red Cell Antigens may cause a Humoral Immune Response Transfusion Science 6 Antigens, Antibodies and the Humoral Immune Response Transfusion Science 7 Red Cell Antibodies Defn. Antibodies are substances produced in response to immunogenic stimulation by foreign antigens and are able to interact specifically with those antigens  glycoprotein molecules  found in all body fluids five classes of Immunoglobulin  IgG IgM IgA IgE IgD IgG and IgM function as Blood Group Antibodies  IgM: directed against carbohydrate/glycolipid antigens  IgG: directed against protein/glycoprotein antigens Transfusion Science 8 Red Cell Antibodies and Clinical Significance IgG and IgM red cell antibodies will react with specific antigen on the red cell surface  cause haemolysis of the red cell in vivo  cause haemagglutination in vitro  antibodies are clinically significant if this results in patient morbidity or mortality   Transfusion Science seen in a number of haemolytic conditions normally caused by a Blood Group incompatibility 9 Red Cell Antigens and Blood Groups over 400 different antigens found on red cell membranes Red Cell antigens are the Blood Groups/Blood Types ‘inherited characters of the red cell surface, detected by a specific alloantibody’ classified into Major & Minor Blood Group Systems (BGS) Transfusion Science 10 Clinically Significant Blood Group Systems 9 Major Blood Group Systems ABO and Rh Blood Group Systems are most clinically significant Blood Group Systems Major Antigens Chromosome Location ABO Rh A, B, D, C, c, E, e 9 MNSs P Kell Duffy Kidd Lewis Lutheran M, N, S, s P1 22 K, k, Jsa, Jsb, Kpa, Kpb Fya, Fyb Jka, Jkb Lea, Leb Lua, Lub 4 Transfusion Science 1 7 1 18 19 19 11 Red Cell Membrane Antigenic Structures red cell antigenic structures composed of  Proteins: e.g. Rh  Carbohydrates: e.g. ABO  Glycoproteins: e.g. Fy (Duffy), MNSs   Lipids/Glycolipids: Transfusion Science 12 ABO Blood Group System Karl Landsteiner discovered the ABO Blood Groups in 1900 most important Blood Group System for transfusion Practice there are 4 main Blood Groups there are only 2 antigens: A & B there is not actually an ‘O’ antigen Transfusion Science 13 ABO Blood Groups thus individuals with Group A red cells have the A antigen protruding from the cell surface A A A A A Group A Red cells A A A Group B red cells have B antigens protruding from the cell surface A B B B B B Group B Red cells B B Transfusion Science 14 B B Schools Education: Paul Watson 2006 ABO Blood Groups thus individuals with Group AB red cells have both A and B antigens on the cell surface B A A Group AB B Red cells A B A Group O red cells have NEITHER A nor B antigens on the cell surface Transfusion Science B B Group O Red cells 15 Schools Education: Paul Watson 2006 Landsteiner’s Law individuals lacking either the A or B antigens on their red cells will have the corresponding antibody in their plasma  this ‘phenomenon’ is only found with the ABO system  Blood GroupAntigen on Red Cells Antibody in Serum A B O AB A B none A&B anti -B anti-A anti-A,B none  anti-A & anti-B are very potent ‘natural’ IgM antibodies with a wide thermal range an ABO incompatible transfusion may result in a fatal haemolytic Transfusion Science 16 transfusion reaction  16 ABO Antigens A and B antigens are distinguished by a specific immunodominant sugar that is attached to a precursor substance  the precursor substance is a carbohydrate chain which is linked to either polypeptides (to form glycoproteins) or to lipids (to form glycolipids)  A and B antigens on red cell membranes are mainly linked to glycoproteins  includes Band 3 integral glycoprotein  the immunodominant sugar that confers A antigen specificity is N-acetylgalactosamine (GalNAc)  the immunodominant sugar that confers B antigen specificity is D-galactose (Gal) Transfusion Science 17 Biochemical Structure of A & B antigens  the terminal structure is a carbohydrate chain, including the immunodomina nt sugar, attached to a membrane bound glycoprotein Transfusion Science  -R -R 18 Rh Blood Group System second most important blood group system in terms of Transfusion Practice RhD positive: the D antigen is present on the red cell surface  highly immunogenic RhD negative: the D antigen is missing from the red cell surface transfusion of an RhD Neg patient with RhD Pos blood may cause an immune response resulting in the production of IgG anti-D  anti-D can cause significant Haemolytic Transfusion Reactions and severe/fatal HDFN Transfusion Science 19 19 Biochemistry of Rh Polypeptides  important integral protein  RhD polypeptide includes the  multi-epitope RhD antigen   RhCE Polypeptide includes other (from Daniels,1995) Rh antigens (C,c,E,e)  the RhD and RhCE polypeptides  are large Transmembrane Polypeptides (417 amino acids long)  RH polypeptides span the membrane 12 times giving 6 extracellular domains arranged in a circular formation   Transfusion Science 20 Function of Rh Polypeptides  RhD & RhCE polypeptides form a macrocomplex with Rh Associated Glycoprotein and other large membrane macromolecules  has a skeletal function & be involved in cation transport across the red cell membrane Transfusion Science 21 The MNSs Blood Group System  discovered in 1927 by Landsteiner and Levine  complex polymorphic system producing numerous antigens  The M and N antigenic structures are found on glycophorin A (GPA)  The S and s antigenic structures are found on glycophorin B (GPB)  these are the large abundant sialoglycoproteins on the red cell membrane Transfusion Science 22 The Duffy Blood group system DARC Glycoprotein with seven membrane spanning domains Red cell receptor for Chemokines Binding Site for Plasmodium Vivax Transfusion Science 23 Blood Group (Pheno)Typing red cell antibodies are specific for the antigen that caused their production react with specific antigen on the red cell surface in an Antigen:Antibody reaction in vitro this can be observed in lab tests as Haemagglutination Transfusion Science 24 Blood Group (Pheno)Typing Antibodies of known specificity can be used as (Pheno)Typing Reagents (aka ‘antisera’) to determine the Blood Type (Group) of an unknown red cell sample Laboratory testing involves incubating reagent antisera (antibody of known specificity) with unknown test red cells: if haemagglutination occurs the specific antigen is present  absence of haemagglutination means specific antigen is not present  for example: anti-D antisera is used to phenotype unknown test cells to see if they are RhD Pos or RhD Neg Transfusion Science 25  Laboratory Practical  You will be reproducing ‘Landsteiner’s’ experiment  this will involve incubating unknown test red cells against unknown test serum from six ‘colleagues’, and observing for (Haem)agglutination  a Direct Saline Haemagglutination technique will be used  from the pattern of Agglutination observed, you will predict the ABO group of each of the six samples Transfusion Science 26