blood bank practicum

what chromosome are the A,B and O genes located on

chromosome 9

what do the A and B genes code for

glycosyltransfereases that facilitate transfer of carbohydrate (sugar) molecules onto carbohydrate precursor molecules

the O gene

an amorph or silent gene

appears to have no gene product

no specific transferase is associated with it

H gene

ABO inheritance is dependent on this to produce H substance on which the A and B Ags are built

what glycosyltransferase does the H gene code for

L-frucosyl-transferase

h gene

extremely rare

fails to produce L-fucosyl-transferase necessary to convert precursor to H substance

no A or B Ags are produced

Bombay phenotype

inherit h gene from both parents (normal people inherit a pair of H genes)

fail to produce H Ag

produce anti-H in their serum without stimulation

appear to be group O but has anti-H

what glycosyltransferase does the A gene code for

N-acetylgalatosaminyltranserase

what glycosyltransferase does the B gene code for

D-galactosyltransferase

when do A and B antigens develop

as early as the 6th week of fetal life

<50% of adult antigen sites are present at birth

Se gene

controls the presence of ABH Ags in secretions

qualitative A subgroups

1-8% of A2 and 22-35% of A2B people produce anti-A1 in their serum which reacts with AI cells and not with self

quantitative A subgroups

A2 cells carry less antigens than A1 cells

about 25% as many A Ag sites as A1 cels

dolichos biflorus

preferred reagent from differentiating A1 and A2

agglutinates A1 and A1B cells NOT A2 or A2B cells

anti-A,B testing

mandatory for all group O donors to confirm that they are not weak subgroups of A

B subgroups

more infrequent than A subgroups

B3,Bx,Bm, and Bel

ABO system antibodies

arise shortly after birth on exposure to environmental

primarily IgM

react best at room temp

capable of activating complement

saline agglutinins

do NOT cross the placenta

anti-A,B

found in all group O sera along with some components of anti-A and anti-B

IgG

more likely to suffer from HDFN

anti-H

found as weak, cold reacting antibodies in some group A1 and A1B people

ulex europaeus

can differentiate among cells with varying concentrations of H Ag

what blood type has the greatest amount of H

type O

what blood type as the least amount of H

type A1B

diseases that may lead to alterations in ABH Ags on RBC surfaces or Ab found patients serum

leukemia - may case a progressive decrease in Ag strength

carcinoma of stomach - may produce excess blood group specific soluble substances which partially or completely neutralize antisera, sufficient washing of patients RBCs prior to testing will result in proper testing

diseases that alter the immune system - may affect Ab level present in serum, Ex: hypogammaglobulinemia, CLL, non-hodgkin’s lymphoma

common sources of technical errors

cell suspensions either too heavy or too light

clerical erros

failure to add reagent

contaminated reagents

warming during centrifugation

discrepancies due to problems with patient’s ABO group

patient’s age (newborns, elderly)

diagnosis

transfusion history

medications

Ig levels

history of pregnancy

weak or missing antibodies

most common cause of ABO discrepancies

seen in newborns, elderly, hypogammaglobulinemia due to leukemias or lymphomas, use of immunosuppressive drugs, immunodeficiency diseases

how to enhance reactions for reverse grouping when suspecting weak or missing antibodies

incubate at room temp for 15 minutes

incubate at 4 C for 15-30 minutes

must use an autocontrol and an O cell control to detect reactivity caused by cold autoagglutinins

causes of weak reacting or missing antigens

subgroups A or B

leukemias or hodgkins disease

excess amounts of blood group specific soluble substances (BGSS) in plasma

causes of unexpected antigens

acquired B - caused by intestinal obstruction, colon, or rectum cancer, and other lower GI tract disorders

protein or plasma abnormalities

rouleaux formation (multiple myeloma, waldenstroms macroglobulinemia, hodgkins lymphoma)

plasma expanders and whartons jelly (viscous material present on cord bloods)

misc discrepancy problems

polyagglutination

cold autoantibodies (positive DAT)

unexpected ABO isoagglutinins

unexpected alloantibodies

warm autoimmune hemolytic anemia

transfusion reactions

lewis system

only system not manufactured by blood cells

Le - codes for enzymes which modify H Ag in secretions

le - amorph

Lele and LeLe - will produce either Lea and Leb Ags dependnet on two other genes (H and Se)

Le + sese or hh - Lea Ag in secretions

Le + Se + H - Lea Ag in secretions

lele - produced no lea and no leb Ags

adsorption of lewis Ags

not intrinsic to RBCs

enters plasma from secretions where Ag precursors are produced by tissue cells

carried into plasma on glycosphingolipids and are adsorbed from plasma to RBC membrane

Le(a+b-)

Le but lacks either Se or H gene

antignes produced - Lea

Le(a-b+)

at least one of each - Le, Se, and H genes

antigens produced - Leb

Le(a-b-)

genotype - lele

antigens produced no Lea and no Leb

lewis antibodies

almost exclusively in Le(a-b-) sera

IgM (does not cross placenta)

poorly developed at birth and not been implicated in HDFN

bind to complement

anti-Lec - reported as a cold reactive

anti-Led - aggluntinates RBCs of Le(a-b-) secretor

where is the gene located for the D antigen

on chromosome 1

what is the most important RBC Ag in transfusion practice after A and B

D antigen

wiener nomenclature

inheritance of a single gene results in the production of agglutinogen(halotype)

agglutinogen = 3 multiple blood factors (Rh Ags)

blood factor and agglutinogen are not one in same

agglutinogen is recognized by a series of reactions of Abs directed agaisnt blood factors

fisher-race nomenclature

most commonly used Rh nomenclature system

Rh Ags - produced under control of 3 sets of allelic genes at very closely linked loci

each gene results in production of an Ag

order of arrangement for linked genes - inherited as a unit

upper case and lower case letters indicate alleles

D, C, E, c, e

rosenfield nomenclature

based on physical expression of Ags

provides no genetic information

Rh 1= D, Rh 2= C, Rh 3= E, Rh 4= c, Rh 5 = e

position effect of Rh gene

cis effect - Rh gene on 1 chromosome affects action of another Rh gene on same chromosome

D gene- produced a weaker expression of E ag

E ag produced by cDE (R2) gene is quantitatively weaker than E produced by cdE

trans effect - Rh gene on 1 chromosome affects action of another Rh gene on opposite chromosome when C is trans to D = weakens D Ag

weak D

quantitative difference in D antigen

characterized by negative reaction with anti-D reagent at immediate spin, negative reaction after 37 C incubation, and positive reaction at anti-human globulin (AHG) phase

weak D - weak expression of Ag (D +w)

low grade weak D - weakly reactive D Ag

quantitative - less D Ag produced

more frequent in black population

generally passed as gene Ro (cDe)

weak D - position effect

high grade weak D

suppression of gene by another gene thru position

c trans effect - most common

quantitative weak D

weak D - D mosaic (partial D)

subunits of D Ag (RhA, Rh B, Rh C, Rh D) are missing

qualitative weak D

very rare

can be sensitized by entire D Ag to produce anti-D

if the patient is transfused with D positive red cells they may develop an anti-D to the part of the antigen that is missing

clinical significance of weak D - donors

weak D positive blood should not be administered to D NEG recipients

weak D Ag may stimulate an immune response in D NEG recipients

donor blood which tests neg with anti-D and pos for weak D - label Rh POS

clinical significance of weak D - recipients

weak D POS recipients - normally classified Rh NEG

• weak D testing not required on recipients, weak D POS would be labeled as D NEG

weak D POS patients - can receive D POS blood

• but does not safeguard against needless sensitization of D mosaic patients, conserves Rh NEG blood supply

Cis - product Ags

cis position effect causes gene/gene complexes which produce a series of interrelated surface structures

when displayed there are numerous possible antigenic subdivision

Abs directed against cis product Ags are infrequent (concealed by other Rh ABs in serum, absorption techniques will demonstrate their presence)

ex: Ce, a cis product which almost always accompanies C and e when gene R1(CDe) is encoded

D deletions

code for Rh material but lack activity at E/e site or at site of both C/c and E/e

some portions of surface configuration are not detectable leaving D only remaining site

if exposed to RBCs through transfusion or pregnancy, form Abs to high incidence Ags - serum will agglutinate all RBCs except those of D homozygotes or Rh null people

ex: CwD/CwD, Dc/Dc,D-/D-

Antigen G

cannot be fitted neatly into concept of 3 antigenic regions

present on all RBC membranes possessing C or D

Abs to this appear to be anti-C/D

variant antigens

subtle differences in composition among various Rh gene products

determined by gene coding for activity which is different from common Rh determinants

seem to reside at same site as C and c, as well as E and e

LW Antigen

strong phenotypical association with Rh system

D POS individuals seem to react stronger with LW Ag(LW1)

D NEG individuals seem to react weaker with LW Ag(LW2)

Rh null syndrome

no Rh Ags are expressed on RBCs

homozygous for amorphic gene (r,r)

no detectable gene products with Rh antiseria

does not code for any Rh system Ags

Rhmod

less than complete suppression of Rh gene

genetic basis is similar to Rhnull

does not completely lack Rh and LW Ags, but shows reduced and variable activity

weak Rh Ags may require elution/absorption techniques to demonstrate their resence

Rh antibodies

IgG

usually results from RBC sensitization (pregnancy, transfusion)

appears 6 weeks - 6 months after exposure to antigen

albumin enhances agglutination

AHG enhances agglutination

enzyme test system - detect weak or developing Rh Ags

high protein anti-D antisera

used in slide, tube, and microplate methods

contains high concentrations of proteins and other macromolecular additives

may cause false POS reactions when tested RBCs are coated with Igs (POS DAT)

low protein anti-D antisera

saline reactive IgM

chemically modified IgG - saline based

monoclonal source anti-D

medium protein anti-D antisera

chemically modified IgG with protein levels between human serum levels and high protein reagents

may cause spontaneous agglutination of some Ig coated RBCs

HDN and anti-D

maternal Abs are coating the newborn’s RBCs

all newborn D Ag sites are occupied by maternal Ab