Lewis System Flashcards
Five characteristics of the Lewis System
It is a system, not a blood group antigen
Cord bloods are always Le(a-b-)
Not manufactured by RBC, not integral, adsorbed onto RBC’s
Decreased expression often seen in pregnant women
Leb expression and immunity are affected by phenotype
What chromosome is Le gene located on?
Chromosome 19 - short arm
FUT3 gene
FUT1 and FUT2 are closely linked on long arm
What does the Le gene code for?
L-fucosyltransferase adds fucose to GlcNAc on type I chains in a 1-4.
Can’t add to type II chains because a1-4 is taken
How is Lea formed?
Lea is formed when a fucose is added to type 1 precursor chains
Only Lea is formed when no Se gene present
How is Leb formed?
Leb is formed when a fucose is added to Type 1 H chains
Se gene forms H substance
Lea is still present but much less than Leb
How is ALeb and BLeb formed?
Se gene forms H substance, A/B genes form A and B substance, Le gene adds fucose > ALeb and BLeb
In group A, most Leb is ALeb
What is Lewis antigen carried on in plasma?
Oligosacchride bound to a lipid
What is Lewis antigen carried on in Saliva?
Oligosacchride bound to a protein
Frequency of Le(a-b+)
72%
80% are secretors
Frequency of Le(a+b-)
22%
20% are non-secretors
Frequency of Le(a-b-)
30% of blacks lack the Le gene
6% of whites lack Le gene
Frequency of Le(a+b+)
16.8% of japenese are Se(w)
also seen in Australian, Chinese, Taiwan, and Polynesians
Se enzyme is ineffective at making H substance to increased Lea antigen
Antigen charactersitics
Not expressed on cord cells
Weaken during pregnancy > Esp Group A women
Resistant to most chemicals
Enhanced by enzymes
Leb is a receptor for…
H. pylori - bacteria responsible for causing gastritis
What is Le(a-b-) associated with?
Increased susceptibility to E. Coli, candida, Cardiovascular disease, and possibly graft failure in renal transplant patients
Group A Secretors
May type as Le(a-b-) because all of Leb is ALeb
What is Le(abx) antigen?
Also called Stage specific embryonic antigen
Carried on fucosylated unbranched type II chains
What is Le(abx) antibody?
Reacts with all cells except le(a-b-) red cells
Reacts with 90% of cord cells (infants with Le gene)
Reacting with type 2 precursor w/ Le fucose
Common and found with anti-Lea and Leb
What are Le(x) and Le(y) antigens?
Isomers of Lea and Leb on Type II chains Not on RBC + Not part of Lewis Fucose + Type II precursor chain = Lex Fucose + Type II H chain = Ley Fucose + H chain + A = ALey Fucose + H chain + B = BLey
Le(c) genetics and antibody
lele, sese
Anti-Le(c) is antibody to precursor type 1 chain or Le(a-b-) non-secretors
adsorbed onto RBC
Le(d) genetics and antibody
lele, Se
Le(d) = Type 1 H chains
Anti-Le(d) only reacts with Le(a-b-) secretors or Type I H chains
ALe(b)
FUT3 adds fucose to A substance
Anti-ALeb reacts with A positive secretors Le(a-b+)
Can’t be seperated into Anti-A and Anti-Le(b)
Group A secretor plasma will adsorb out regardless of Lewis type
BLe(b)
FUT3 adds fucose to B substance
Anti-BLeb reacts with B positive secretors Le(a-b+)
Group A secretor plasma will adsorb out regardless of Lewis type
Diseases associated with loss of Lewis antigens
Infectious mononucleosis
Severe alcoholic cirrhosis
Alcoholic pancreatitis
Disease associated with increased Lewis antigens
Fucosidosis
Describe Lewis antigen developement
At birth infant is Le(a-b-) 2 months type as Le(a+b-) transitional period of Le(a+b+) 2-3 years true typing can be determined 5-6 years Lewis antigen fully developed
Characteristics of Lewis antibodies
Fragile, weak agglutination
Hemolysis rarely seen in vitro (enzyme treated cells increases)
IgM reacts at RT
Naturally occurring
Not clinically significant cause Le antigens can elute off cells
Anti-Lea and anti-Leb often occur together
Anti-Le(bH)
Reacts with O and A2 cells Le(a-b+)
Anti-Le(bL)
True anti-Leb
Reacts with all Le(a-b+) cells
