blood bank exam 2

who discovered ABO system

landsteiner

A and B Ag freq in caucasians

O 45%

A 40%

B 11%

AB 4%

ABO Ags are expressed on

RBCs, lymphocytes, platelets, tissue cells, bone marrow, and solid organs

O gene is an

amorph, autosomal recessive

A and B Ags are built from

H antigen

ABH Ag formation results from interaction of genes at

ABO, Hh, and Se loci

glycosyltransferases

cause transfer of monosaccharide onto a precursor substance on RBC

type 1 precursor chains

in secretions

Gal-B(1→3)-GlcNAc

type 2 precursor chains

on RBC surface

Gal-B(1-4)-GlcNAc

H gene

codes for fucosyltransferase (FUT1) that adds fucose to terminal galactose of type 2 precursor chains

A gene

codes for transferase that adds N-acetylgalactosamine (GalNAc) to subterminal galactose of preformed H antigen

B gene

codes for a transferase that adds D galactose (Gal) to subterminal galactose of preformed H antigen

H gene glycosyltransferase

a 2 L fucosyltransferase

H gene immunodominant sugar

L fucose

A glycosyltransferase

a 3 N acetylgalactosaminyltransferase

A immunodominant sugar

N acetyl o galactosamine

B glycosyltransferase

a 3 o galactosyltransferase

B immunodominant sugar

D galactose

AB antigen is from

N acetyl galactosaminyl and galactosyl transferases

RBCs of newborn compared to adult

25-50% the number of antigenic sites

reaction of newborn RBCs with abo reagent antisera are frequently

weaker than adults

FUT 1 (H) and FUT 2 (Se) are

closely linked and located on chromosome 19

Se gene must be inherited to form

ABO antigens in secretions

secretor

Se gene (FUT2) encodes fucosyl transferase that adds fucose to type 1 precursor chains forming type 1 H antigens

Type 1 H can be modified by A or B transferases to make

soluble A and B antigens

secretor freqs

80% has at least one copy of Se

20% has sese (nonsecretors, no abh in secretions)

ABO gene location and exons

chromosome 9, 7 exons

exons 6 and 7 of ABO gene code for

catalytic domain of ABO glycosyltransferases

amino acid substitutions within the 6 and 7 exon of ABO gene is responsible for

less efficient transfer of immunodominant sugar to H substance, resulting in weak serologic reactions observed in ABO subgroups

A subtypes

A1 and A2

Type A1 freq

80%

Type A2 freq

20%

anti A1 is present in ____ of A2

1-8%, only clinically sig if warm reacting

anti A1 is present in ___ of A2B

22-35%

A1 lectin

dolichos biflorus

lectin

seed extract that agglutinates human cells with specificity

dolichos biflorus

agglutinates A1 or A1B

bandeiraea simplicifolia

agglutinates B cells

Ulex europaeus

agglutinates O cells (H specificity) and other ABO blood groups depending on amt of H

bombay

no H on Ag surface

weak subgroups of A often have ___ between amt of H Ag on RBC and amt of A Ags formed

inverse reciprocal relationship (more A Ag → less H Ag expressed on RBC)

Anti H is occasionally found in

serum

H antigen

naturoly occurring IgM cold agglutinin that reacts best below room temp, can cause problems in screenings, use anti H lectin

rank greatest amt of H to least

O > A2 > B > A2B > A1 > A1B

Weak A subgroup characteristics

decreased A Ag sites per rbc

agglutination with anti A and B

strong reactions with anti H

presence or absence of anti A1

Weak A subgroups

A3, Ax, Aend, Am, Ay, Ael

weak B subgroups

if forward or reverse is not over 2+, very rare, result of alt alleles at B locus

criteria for differentiation of weak B

agglutination with anti B AB and H

presence or absence of ABO isoagglutinins in serum

adsorption elution studies with anti B

presence of B in saliva

molecular tests

B3 has

mf anti B and anti AB

A3 has

mf anti A and anti AB

bombay phenotype

hh, types as group O but reverse wont match

identifying bombay

ulex europeus lectin wont agglutinate

bombay anti H

potent and reacts at 37

Oh can

bind complement and cause RBC lysis (IgM)

para bombay phenotypes

rare phenotypes with RBCs completely devoid of H antigens, mutated FUT1 gene and fucosyltrnsferase enzyme activity is reduced, only detectable with adsorption and elution

ABO antibodies are well developed

4 months of age from cord blood serum

anti AB

separate cross reacting Ab that is IgG, not a mixture of anti A and anti B, found in group O, more effective at detecting weak A and B Ags, used in neonates or discrepancies

conditions that weaken antigen strength

leukemia, chromosome 9 translocations, hemolytic diseases, hodgkins disease, lymphomas

acquired B

phenomenon in group A1 caused by intestinal obstruction, carcinoma of colon or rectum, or others that increase permeability of intestinal wall that allow polysaccharides from E colon into the blood, group A RBCs absorb B polysaccharide which reacts with anti B

acute hemolytic transfusion reaction symptoms

fever, kidney failure, diffuse clotting and bleeding, death

anti A color

blue

anti B color

yellow

specimen for abo typing muat be

less than 3 days old

group I discrepancy

weakly reacting or missing Abs on reverse

group II discrepancy

weakly reacting or missing antigens on forward

group III discrepancies

unexpected extra reactivity on reverse

group IV discrepancy

misc

causes of group I discrep

newborn, elderly, transfusion recipient, cold reacting autoAb, leukemia, lymphoma, immunosuppressed, stem cell transplant

how to resolve group 1 discrep

increase incubation time to 30 min, lower temp to 4C for 15 min, include O cells and autocontrol

why is O and autocontrol needed with resolving group I discrep

lowering temp can enhance cold reacting agglutinins

group II discrep causes

age, colon/gi cancer, transfusion, transplant, leukemia

group II examples

weak or missing Ags on forward type, unexpected pos reactions with red cells, weak B

how to resolve acquired B

acidify anti B to pH of 6, run DAT, run autocontrol

resolving group I discrep

incubate RBCS for 30 min, then incubate at 4C for 15-30 including group O and autocontrol, modify pH if acquired B

group III discrep examples

unexpected extra reactivity on reverse, excess plasma protein from multiple myeloma or whartons jelly on cord blood, rouleaux

resolving group III discrep

wash rbcs with saline, saline replacement of serum(dont replace in AHG tests)

group III discrep would test

agglutinates with all reagents

group IV discrep examples

cold autoAbs coating RBCs, mismatched transfusion or stem cell transplant, A2 or A2B unexpected ABO antibodies

in a group IV, potent cold auto Abs can yield a

pos DAT or IAT

resolving group IV discrep

run DAT and ABSC, incubate in warmer and wash with warm saline, if not resolved then treat RBCs with DTT

test for A2 or other unexpected alloantibodies such as IgM

group IV discrep would test

2+ reactions of 1 type and 4+ reactions of another

A subgroup would test

weak A1 reaction but 0 A2 or A1 lectin reaction

common cold reacting alloAbs

anti M, anti P1, Anti Lea or Leb

how to resolve cold reacting alloAbs (false pos in plasma)

ABID, incubate warm, neutralize with P1 and lewis procedures, use Ag neg reagent cells

common cold reacting autoantibodies

anti I

how to resolve cold reacting autoantibodies

use Ag neg reagent cells (cord cells lack I)

chimerism

presence of 2 cell populations in single individual, caused by teins, dispermy, blood or stem cell transfusion, fetal maternal bleeding

Rh antibodies are only produced

after exposure to foreign RBCs

Rh antigens are made of

proteins

ABH Ags are made of

carbohydrates

Rh pos individuals inherited

at least one copy of RHD gene

Rh Ags are encoded by

RHD gene on chromosome 1

C and E antigens are

antithetical antigens

C and E are present on

RhCE protein encoded by RHCE gene on chromosome 1

fisher race nomenclature

D, C, E, no D if not inherited

DCE genes are

linked

weiner believed

only 1 gene responsible for defining Rh that produced an agglutinogen

agglutinogen

phenotypic expression of haplotype, each factor is antigen recognized nu Ab

Weiner nomenclature

Rh pos = R

Rh neg = r

C or E is superscripts

Rh pos haplotyped weiner

R0, R1, R2, Rz