Ii Blood Group Flashcards
The branching process is controlled by______ enzymes, which add sugars to the straight chains of i, converting them into branched I structures
glycosyltransferase enzymes
• Newborns predominantly express the____ antigen (their RBCs are rich in linear carbohydrate chains).
• Over the first 18 months of life, the____ antigen decreases as enzymatic branching converts it into____ antigen.
• By adulthood, RBCs contain predominantly____ antigen with only trace amounts of___ remaining
i antigen
i; I
I; i
Some individuals do not undergo this normal transition and retain the i antigen into adulthood. These individuals have the_____phenotype, which is genetically distinct and results from mutations affecting the enzyme responsible for branching.
i adult
_____ is a common naturally occurring antibody.
• Cold-reacting IgM antibody, often seen in healthy individuals.
• Can cause cold agglutinin disease (CAD), a type of autoimmune hemolytic anemia where RBCs clump at cold temperatures.
Anti-I
____is much rarer but can be associated with:
• Some cases of infectious mononucleosis (caused by Epstein-Barr virus)
• Certain hematologic disorders
Anti-i
Proteolytic enzymes (2) enhance the reactivity of both I and i antigens with their respective antibodies.
ficin and papain
(2) do not destroy I and i antigens, meaning they are resistant to these chemical treatments.
Dithiothreitol (DTT) and glycine-acid EDTA
______ is commonly associated with cold agglutinin syndrome (CAS), where the antibody binds to I-positive RBCs at low temperatures.
• This can lead to hemolysis (destruction of RBCs) when the immune system mistakenly attacks them.
Anti-I
•_____ is sometimes detected in patients with infectious mononucleosis, where the Epstein-Barr virus (EBV) triggers an immune response.
• This antibody is usually transient and not clinically significant.
Anti-i
• I antigen is formed by the action of the IGnT gene, which is located on chromosome____
6
formation is not entirely understood, but it serves as the precursor for I antigen.
i antigen
As the person matures, small i antigen is enzymatically converted into branched I antigen with the help of the______.
IGnT gene
Molecular Structure
• Both I and i antigens are formed on precursor______ chains of RBCs.
A, B, and H
The H antigen substrate and I antigen share the same precursor:
• ______+______
• However, the I antigen lacks additional sugars, such as fucose and/or galactose, which are present in H antigen.
Lactosylceramide + Paragloboside
_____+_______+______→ i Antigen (Linear, small structure)
Lactosylceramide (Glc-Gal) +
N-acetylglucosamine +
Galactose
→ I Antigen (Branched, larger structure)
i Antigen +
N-acetylglucosamine +
Galactose
facilitates the conversion of small i antigen into big I antigen.
IGnT gene
Ii Antigens and Their Reactions with Antibodies
• Enzymatic Effects: (2)
• Resistant to:
• Ficin → Produces 2 end products
• Papain → Produces 3 end products
• Dithiothreitol (DTT)
• Glycine-acid EDTA
In adults (I antigen present): _____strongly reacts because I antigen is dominant.
Anti-I
In newborns (i antigen dominant): ____reacts strongly since I antigen has not yet developed.
Anti-i
In the rare adult i phenotype: Since conversion is incomplete, i antigen remains, leading to a strong reaction with____ and weak reaction with____.
anti-i
anti-I
• Clinically insignificant → Does not cause hemolysis or any blood-related disorder.
Benign Autoanti-I
• It is naturally occurring and non-pathologic (does not cause disease).
• Common in virtually all individuals (trace amounts present in normal sera).
• Reacts at 4°C (cold IgM autoantibody).
Benign Autoanti-I
• Causes Cold Agglutinin Disease (CAD), a type of autoimmune hemolytic anemia
Pathologic Autoanti-l
• IgM in nature but pathogenic.
• Produced after Mycoplasma pneumoniae infection.
• Reacts at room temperature and at 4°C, meaning it can agglutinate RBCs even at normal body temperatures.
Pathologic Autoanti-l
• Very rare because most adults have the I antigen.
• Present in individuals with the adult i phenotype (who fail to convert i antigen to I).
• Can be IgM or IgG.
Alloanti-I
• Uncommon antibody, but can be found in:
• Epstein-Barr virus (EBV) infection (infectious mononucleosis).
• Asian individuals with congenital cataracts.
• Can be IgM or IgG
Anti-i
Laboratory Testing for Ii Antibodies
Test Condition
Effect on Ii Antibodies
Pre-warming the test
Enzyme treatment (ficin, papain)
Eliminates reactivity of insignificant anti-I (avoids cold agglutination).
Enhances detection of anti-I and anti-i.
Anti-I is associated with:
• Cold Agglutinin Disease (CAD)
• Mycoplasma pneumoniae infection
Anti-i is associated with:
• Infectious mononucleosis (Epstein-Barr virus)
• Congenital cataracts (seen in Asians with the rare adult i phenotype)
i Antigen is increased in disorders of RBC maturation, including:
• Dyserythropoiesis (abnormal RBC development)
• Acute leukemia
• Hypoplastic anemia
• Megaloblastic anemia
• Sideroblastic anemia
• Thalassemia
• Paroxysmal nocturnal hemoglobinuria (PNH)
• Sickle cell disease
• Chronic hemolytic anemia
