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 1ST
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

4. 2 IMPORTANT CHARACTERISTICS
deformability
•ATP↑
•Ca inside cell ↓
•Phosphorylation of spectrin ↑
permeability
•Freely to water and anions
•Impermeable to cations (Na+ 1:12, K+ 25:1)
•Ca2+
pumped out (calmodulin)

7. 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

8.  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

9. RBC MEMBRANE PROTEINS
Transmembrane/integral
(Serve as transport and adhesion sites and signalling receptors)
Band 3
Glycophorins
Rh proteins
Kell & duffy Ags
ATPase(Na-K, Ca, Mg)

10. 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

11.  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

12.  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

14. 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

15. 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)

16. 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

19. 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

20.  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

21. 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,

22. Spherocytes

23. SCHISTOCYTES - Helmet cells,
bite cells, etc

24. SDS- PAGE

25. 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%

26. 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

27. 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

28. 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

29. PBS
Cigar shaped elliptocytes
Spherocytes
Stomatocytes
Fragmented red cells

30. 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

31.  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

32. OTHER RBC MEMBRANE
DISORDERS

33. 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

34. 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

35. THANK YOU