Red Blood Cell Antigens and Blood Typing

Red Blood Cell Antigens and Blood Typing (ABO system) • Antigens: found on the surface of cells to help immune system recognize self cells • Antibodies: secreted by lymphocytes in response to foreign cells • ABO system: antigens on erythrocyte cell surfaces a.Type A - has the A antigen b.Type B - has the B antigen c. Type AB - has both the A and B antigens d.Type O - has neither the A nor the B antigen Sheet Note 1 ‫ و بطلع على‬، ‫ موجود بكل خاليا الجسم‬Antigen ‫ هو عبارة عن‬MCH 1 ‫ال‬ ‫ انا خلية‬: ‫ زي كأنها بتنادي باقي الخاليا و بتقول‬infected ‫السطح اذا صارت الخلية‬ ‫مصابة‬ In ABO system 1. We have 4 phenotype . 2. We have 3 alleles . 2 Continue… • The plasma contains antibodies against the antigens not present on the RBC Agglutination Reaction a. Type A – has anti-B antibodies b. Type B – has anti-A antibodies c. Type AB – has no antibodies (universal recipient) d. Type O – has anti-A and anti-B antibodies (universal donor) • Transfusion reaction - If a person receives the wrong blood type, antibodies bind to erythrocytes and cause agglutination. • The A and B antigens are inherited as mendelian allelomorphs, A and B being dominants (E.g. an individual with type B blood may have inherited a B antigen from each parent or a B antigen from one parent and an O from the other) • The prevalence of the different blood types among one group of persons studied was approximately: O 47%, A 41%, B 9%, AB 3% Sheet Note 2 ‫ بميزه‬cell surface ‫ هو بروتين موجود على ال‬Antigen ‫اللي بهمنا نعرفه انه ال‬ immune response ‫ و ما بهاجمه و ما بعمل‬immune system ‫ال‬ - Type A Type B Antigens on red blood cells Antibodies in plasma Agglutination reaction 3 Titer of the Agglutinins at Different Ages • Immediately after birth, the quantity of agglutinins in the plasma is almost zero. • 2-8 months after birth, an infant begins to produce agglutinins (anti-A agglutinins when type A agglutinogens are not present in the cells, and anti-B agglutinins when type B agglutinogens are not in the cells) • A maximum titer is at 8 to 10 years of age • The titer gradually declines throughout the remaining years of life. Origin of Agglutinins in the Plasma • Agglutinins are gamma globulins Antibodies • They are produced by the same bone marrow and lymph gland cells that produce antibodies to any other antigens. • Most of them are IgM and IgG immunoglobulin molecules. Sheet Note 3 ‫ بتفاعل‬، ‫ بصير في حال حدوث خطأ بنقل الدم‬agglutination reaction ‫ال‬ Hemolysis of RBCs ‫ و بعديها بصير‬Antigen ‫ مع ال‬Antibody ‫ال‬ Agglutinin = Antibody Agglutinogen = Antigen 4 Agglutination can be used for blood typing • Agglutination plug small blood vessels throughout the circulatory system  Physical distortion of the cells or attack by phagocytic WBC destroys the agglutinated cells membrane  releasing hemoglobin into the plasma causing hemolysis of the RBCs. • Acute Hemolysis: When the recipient and donor bloods are mismatched • Before giving a transfusion to a person, it is necessary to determine the blood type of the recipient’s blood and the blood type of the donor blood so that the bloods can be appropriately matched This process is called: Blood typing and blood matching 1. The RBCs are first separated from the plasma and diluted with saline solution. 2. One portion is mixed with anti-A agglutinin and another portion with anti-B agglutinin. 3. After several minutes, the mixtures are observed under a microscope. 4. If the RBCs have become clumped “agglutinated”  an antibody-antigen reaction has resulted. 5. Type O blood have no agglutinogens and therefore do not react with either the anti-A or the anti-B agglutinins. 6. Type A blood has A agglutinogens and therefore agglutinates with anti-A agglutinins. and agglutinates with anti-B agglutinins. Type B blood has B agglutinogens. Type AB blood has both A and B agglutinogens and agglutinates with both types of agglutinins. Anti-B Anti-A Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Type A Type B Type AB 5 Rhesus (Rh) factor Sheet Note 5 Short important video about ( Rh )and (Erythroblastosis fetalis) • Antigen D is the most popular, while (C, E, c, d, e) are very less popular • Rh-positive has the D antigen • Rh-negative does not have the D antigen; will not have antibodies unless exposed to Rh+ either through a blood transfusion or pregnancy • Issues in pregnancy - An Rh− mother exposed to Rh+ fetal blood produces antibodies. This may cause erythroblastosis fetalis in future pregnancies as antibodies cross the placenta and attack fetal RBCs. Rh- mother is treated with RhoGAM that inactivates the antigens • Rh Transfusion Reactions • If an Rh-negative person has never been exposed to Rhpositive blood, transfusion of Rh-positive blood into that person will likely cause no immediate reaction • The anti-Rh antibodies can develop in sufficient quantities during the next 2 to 4 weeks to cause agglutination of the transfused cells that are still circulating in the blood  hemolyzed by the macrophage • With multiple exposures to the Rh factor, an Rh-negative person eventually becomes strongly “sensitized” to Rh factor 6 The human leukocyte antigen (HLA) system • The HLA system is the major histocompatibility complex [MHC] in humans • it is an important part of the immune system and is controlled by genes located on chromosome 6. • It encodes cell surface molecules specialized to present antigenic peptides to the T-cell receptor (TCR) on T cells • MHC molecules that present antigen are divided into two main classes: 1) Class I MHC molecules: present on the surface of all nucleated cells (If the cell is infected by a virus, the HLA system brings fragments of the virus to the surface of the cell so that the cell can be destroyed by the immune system.) Foreign antigens presented by MHC class I attract T-lymphocytes called Killer Tcells killer T-cells that destroy cells. 2) Class II MHC molecules: present only on professional antigen-presenting cells (B cells, macrophages, dendritic cells, Langerhans cells), thymic epithelium, and activated T cells) • Mutations in HLA genes may be linked to autoimmune disease such as type I diabetes, and celiac disease. 7