RBC MEMBRANE STRUCTURE AND ITS DISORDERS.pptx

RBC Membrane structure and its disorders. I am Dr. Samhati Tripathy from Department of Transfusion Medicine, S.C.B. Medical College, Odisha, India. Here, we will discuss structure of RBC membrane in detail with its receptors, their significance and the disorders arising out of it. Enzyme disorders are not included here.

1. RBC MEMBRANE STRUCTURE AND ITS DISORDERS DR. SAMHATI TRIPATHY PG 1 ST YEAR RESIDENT DEPT OF TRANSFUSION MEDICINE S.C.B. M.C.H.

2. introduction Biconcave--40% excess surface area allows it to stretch upto 2.5 times Volume 90 fl RBC membrane represents a semipermeable lipid bilayer supported by a mesh-like cytoskeleton

3. 2 impORTANT characteristics

4. RBC MEMBRANE LIPIDS 8% carb , 52% proteins, 40% lipids Lipid portion contains equal parts of cholesterol and phospholipids which form a bilayer The hydrophilic polar head of PL faces outwards towards both the aqueous plasma and cytoplasm The hydrophobic nonpolar acyl tails of PL arrange to form a central layer The esterified cholesterol being hydrophobic lies parallel to the acyl tails of phospholipids and confers tensile strength Membrane enzymes maintain the cholesterol conc.(LCAT-lecithin cholesterol acyltransferase ) Rise in cholesterol conc increases strength but reduces deformabilty

5. The PL are asymmetrically distributed Outer layer – phosphatidylcholine & sphingomyelin Inner layer – phosphatidylserine & phosphatidylethanolamine Membrane PL and cholesterol may also redistribute laterally to deform in response to stress

6. RBC MEMBRANE PROTEINS

7. Glycophorins Alpha helix made of hydrophobic amino acids with hydrophilic (negatively charged) sialic acid-rich intra and extra cellular domain. This – ve charge prevents clumping of RBCs to each other Act as transmembrane receptor for entry of plasmodium into RBC So, if absent----protected from malaria Also carry blood group antigens- A,B- MNSs C,D- Gerbich

8. Band 3 Mediates exchange of Cl - ions(in) with HCO3- (out) across membrane Diego antigen Age related marker on RBC- aggregation of band 3—autologous IgGs bind to it-triggers phagocytosis by liver and spleen macrophages

9. CR1(complement receptor) aka CD35- -regulator of complement system(avoid autologous complement attack due to deposition of naturally occuring IgG autoAbs - phagocytosis of ring stage Pf by complement activation CD55/DAF- pf attachment to RBC surface. CD55 null RBCs are refractory to invasion Duffy- receptor for pv ---absent--resistant Kidd- functions as urea transporter Basigin - recirculating mature RBCs from spleen, Ok antigen

10. CYTOSKELETAL PROTEINS Supporting framework for the lipid bilayer ---give it shape to make it biconcave Protein 4.1 Protein 4.2 Actin Contraction and relaxation of membrane

11. Spectrin helical flexible heterodimers made of 2 polypeptide chains- α and β Each actin oligomer can bind multiple spectrin tetramers creating a 2D spectrin-actin skeleton that is connected to the CM by 2 distinct tethering interactions- ankyrin and band 4.2 protein 4.1 (binds spectrin to band 3) (binds tail of spectrin to GP)

12. HEREDITARY SPHEROCYTOSIS Inherited intrinsic RBC membrane defect that render red cells spheroid, less deformable and vulnerable to splenic sequestration and destruction Northern Europe – 1:5000 75% AD, 25% AR(protein 4.2 , Japan) Rest are compound heterozygosity for 2 different defects---more severe, marked jaundice at birth, requires exchange transfusion

13. diagnosis Family history CBC— Hb,MCV MCHC,RDW Peripheral blood smear- Reticulocyte count ↑ S. indirect bilirubin ↑ S. LDH ↑↑ S. haptoglobin ↓↓ OFT, AGLT(acidified glycerol lysis test)—uses hypotonic soln Cryohemolysis test—uses hypertonic solution

14. EMA(eosin-5-maleimide binding test-flowcytometric test to observe CM protein interaction with EMA dye SDS-PAGE(sodium dodecyl sulfate polyacrylamide gel electrophoresis)—to quantify each protein Ektacytometry- reveals characteristic response of RBC memb to laser diffraction biomechanical stressors LC-MS/MS(mass spectrometry)— analyse the protein composition of RBC memb

15. HISTOPATH. FINDINGS Spherocytosis ---most specific, but npt pathognomonic Anisocytosis , poikilocytosis , target cells Reticulocytosis ---compensatory change—5-20% Marrow erythroid hyperplasia Hemosiderosis —repeated BT Howell Jolly bodies (small dark nuclear remnants) in splenectomised patients Osmotic fragility test MCHC , RDW ↑ Schistocytes on PBS,

16. Spherocytes

17. sCHISTOCYTES - Helmet cells, bite cells, etc

18. SDS- PAGE

19. CLINICAL FEATURES chronic hemolytic anemia of mild to mod severity---pallor, fatigue,dyspnea , tachycardia splenomegaly ---mod-—early satiety, LUQ pain Jaundice Cholelithiasis —pigment stones—40-50%

20. COMPLICATIONS Aplastic crisis—triggered by parvovirus B19 infection---because it infects and kills red cell progenitors Hemolytic crisis—increased splenic destruction---- trigerred by infectious mononucleosis infection Neonatal jaundice, non-immune hydrops fetalis -----with fetal death if severe

21. TREATMENT Phototherapy, exchange transfusion Folic acid supplements Blood transfusion Splenectomy -anemia is corrected but spherocytes persist Cholecystectomy —for GB stones Iron chelation therapy—for hemosiderosis

22. HEREDITARY ELLIPTOCYTOSIS Loss of the normal elastic recoil property in RBCs within the peripheral circulation, resulting in their distinct elliptical shape— extravascular hemolysis African & mediterranean Defect in spectrin >ankyrin,4.1, band 3, actin AD A subtype of HE- hereditary pyropoikilocytosis (HPP) has AR inheritance

23. PBS Cigar shaped elliptocytes Spherocytes Stomatocytes Fragmented red cells

24. Types of he BASED ON variatons in RBC morphology and degree of hemolysis -- Common hereditary elliptocytosis —m/c, asymptomatic. Neonates may have transient hemolysis which resolves within first year Hereditary pyropoikilocytosis (HPP)—most severe, uniquely susceptible to thermal stressors. Neonatal jaundice and persistent hemolytic anemia throughout life. On PBS- microspherocytes , poikilocytes with rare elliptocytes

25. Southeast asian ovalocytosis (SAO)—seen in malaria endemic regions—confers some protection mild to no hemolysis band 3 defect PBS- stomatocytes with longitudinal slits Spherocytic elliptocytosis (SE)– Italian, mod hemolysis Majority are asymptomatic-- don’t need any t/t Folate supplementation If symp – BT, splenectomy

26. OTHER RBC MEMBRANE DISORDERS

27. Hereditary stomatocytosis / xerocytosis Mutations in PIEZO1 gene Increased permeability to cations Greater efflux of K + than Na + ----net decrease in cation content--- osmotically resistant xerocytes —rigid RBCs ---destroyed by spleen— hemolysis (compensated) AD PBS – macrocytic stomatocytosis Decreased OF C/F-fatigue, jaundice, pallor, dark urine esp during intense physical activity T/t not needed

28. cryohydrocytosis Mutation in band 3---convert the anion exchanger into a nonselective cation channel Lyse when stored at 4 ̊ C AD Pseudohyperkalemia due to K + leakage

29. THANK YOU