Lewis Flashcards
The_________ is unique among blood group systems because these antigens are not part of the red blood cell (RBC) membrane itself.
Instead, the antigens exist in the_____ and passively adsorb onto the RBC membrane from circulating glycolipids.
Lewis blood group system
plasma
This means that Lewis antigen expression on RBCs can change depending on an individual’s…(2)
secretor status
plasma composition
ISBT symbol
LE
ISBT NUMBER
007
GENE PRODUCT
Alpha-1-4-L-fucosyltransferase (FUT3)
Consists of two antigens:
Le^a
Le^b
●
– produced if (+) Le gene
Le^a
●
– produced if (+) Le and Se gene
Le^b
has the same precursor as ABO Antigen →_______
TYPE 1 paragloboside (found on secretions only)
Secretions (4)
Saliva
sweat
tears
breastmilk
Genes involved
(Found at Chromosome 19)
Le
Se
H
Le
Enzyme
Alpha 1,4-L-fucosyltransferase
Se
H
Enzyme
Alpha 1,2-L-fucosyltransferase
compete with each other in whoever adds fucose first to the paragloboside
● Le & Se
○ If Le adds fucose first =
○ If Se adds fucose first , Le can still add fucose =
Le^a
Le^b
ABO and Lewis antigens can coexist b/c they have the same precursor
Type 1 paragloboside
● If Le gene is the ONLY PRESENT and adds fucose sugar, it
forms the______
● If BOTH Le gene and Se gene are present, Le^a gene WILL NOT
be produced but the______
● If H gene is the ONLY PRESENT and adds fucose sugar, it forms
______
● If BOTH Le gene and H gene are present,_____ antigen will still
be formed
Le^a phenotype/antigen
Le^b gene
H phenotype/antigen
Le^a
Recall that in order to have Le^b gene, presence of_____ and _____ SHOULD be presen
Le gene and Se gene
Antigens are resistant to
Ficin
Papain
DTT
Glycine-acid
EDTA
Antibody
- Most commonly encountered
- Often IgM; sometimes IgG
ANTI-Le^a
Antibody
- Not common and not as reactive
- Does not readily fix complement
- Anti-Le^bL and Anti-Le^bH
ANTI-Le^b
Antibody
- Formerly known as anti-Lex
- Agglutinates Le (a+b-) and Le(a-b+)
cells - Formed by all Le(a-b-)
ANTI - Le^ab
– present in the secretions, plasma and other tissues; B1→3 linkage
TYPE 1
– present in RBCs; B1-4 linkage
TYPE 2
_____enzyme adds fucose specifically to the 4th carbon of GlcNac.
FUT3
are amorph
○ They do not encode for any transferase enzyme; no antigen expression
se and le
Transfers L-fucose to the 4th carbon of GIcNAc of the type 1 chain and forms Le^a
Is in intimate association with Se and ABH genes in the formation of Leb
Alpha-4-L-fucosyltransferase
antigen is consistently found in the plasma of individuals, irrespective of their secretor status.
Le^a
Formation of Lea Antigen
• The Lewis (Le) gene encodes the enzyme α-1,3/4-fucosyltransferase, which adds____ to the type 1 precursor chain (found in body fluids).
• When only the Le gene is present, the____ antigen is produced.
• However, since this antigen forms in secretions first and is then absorbed onto RBCs, Le(a+) individuals are usually ABH non-secretors (sese).
fucose
Lea
Formation of Leb Antigen
• If both the Le and Se genes are present, the secretor enzyme (FUT2) first converts the precursor substance into____ antigen.
• The Lewis enzyme (FUT3) then acts on this H antigen to form____ antigen.
• This means that Leb antigen is only formed in individuals who are both_____ and _____ positive
H
Le^b
Lewis-positive (Le) and Secretors (Se).
Individuals with the lele Genotype (Lewis-negative)
• If a person inherits two non-functional le alleles (lele), they cannot produce____ antigens.
• These individuals have the ______phenotype and may be either ABH secretors or non-secretors.
Lewis
Le(a–b–)
Lele or LeLe, sese
Phenotype???
Le(a+b-)
Lele or LeLe, SeSe or Sese
Phenotype???
Le(a-b+)
lele, SeSe, Sese, or sese
Phenotype???
Le(a-b-)
LeLe or Lele, SeSe or Sese (Incomplete enzyme activity)
Le(a+b+) (Rare)
individuals (Leb positive) are the most common phenotype in whites and blacks.
Le(a–b+)
individuals (Lewis-negative) are more common in blacks than in whites.
Le(a–b–)
individuals are rare in whites and blacks but more common in Asians (10–40%).
Le(a+b+)
Lewis Antigens Are Not Found on______ RBCs:
• Cord blood RBCs lack Lewis antigens.
• Lewis antigen expression is acquired during the first few years of life as the glycolipids accumulate in plasma.
• Pregnancy reduces the expression of Lewis antigens, leading to weaker antigen expression on maternal RBCs.
Newborn
Lewis Antigens Are Resistant to Enzymes:
• Lewis antigens are not destroyed by common enzymes like (4)
• Instead, enzyme treatment enhances Lewis antibody reactivity, leading to stronger agglutination or even hemolysis.
ficin
papain
dithiothreitol (DTT)
glycine-acid EDTA.
T or F
Lewis antibodies are naturally occurring antibodies that are produced without prior exposure to red blood cells (RBCs).
TRUE
Unlike other clinically significant blood group antibodies, Lewis antibodies are usually______, which means they do not cross the placenta and do not cause hemolytic disease of the fetus and newborn (HDFN).
IgM
Lewis antibodies are produced by ____ individuals
Le(a-b-) individuals
is the most commonly encountered Lewis antibody and is usually IgM.
Naturally occurring and produced by Le(a–b–) individuals.
Anti-Le^a
Lewis antibodies
Reacts more in_____ than in blood groups _____ and ____
○ Because _____ has more H antigen
group O than A or B
Group O
May activate complement and may cause in-vivo and in-vitro
hemolysis
Lewis antibodies
Occur frequently in pregnant women
○ diluted Le a and Le b
■ Due to plasma volume expansion
Lewis antibodies
Most commonly encountered antibody
ANTI-Le^a
→ produces Anti-Leª (antibody)
Le^b Antigen
Not common and not as reactive
Since the concentration of Le gene is smaller than Se (secretor) gene
ANTI-Le^b
Formerly known as anti-Le^x
ANTI-Le^ab
This antibody will only be formed, when the patient’s blood type is null or Le(a-b-)
ANTI-Le^ab
