Blood bank

most blood groups follow a straightforward

autosomal codominant inheritance pattern

the antigens expressed on blood cells are called

phenotype (what is seen)

phenotypes are controlled by

genotypes

population genetics as used in blood banking focuses on

Mendel’s Laws of Inheritance and the Hardy-Weinberg Equation

RR or rr are

homozygous, have same alleles on both parental gametes

Rr is

heterozygous, different alleles on each partental gamete

R is ________, meaning that plants with that gene will

dominant, have that trait shown

r is

recessive

Mendels first law, states that

Law of Independent Segregation, allele pairs separate during the formation of gametes

most blood cells groups exhibit

codominance

if gene is codominant then

both alleles are expressed

Mendels second law, states that

law of independent assortment, different traits are inherited separate from each other

If two traits are physically near each other on the chromosome, they are considered _____, and may be inherited together as a

linked, haplotype

results in a idfferent prevalance then if inhertiance followed random assortment

linkage disequilibrium

Hardy-Weinberg equation

p + q =1, p stands for gene frequency of dominant allele and r the recessive

Hardy-Weinberg equation for heterozygous populations

p² +2pq +q²=1

phenotype calculation (for one type)

number of units to test = # units desired/antigen - negative frequency

phenotype calculation (for multiple types)

number of units desired = # units desired/ (ag - negative frequency1)(ag - negative frequency 2)

molecular testing results provide an individuals

genotype

the genetic basis for blood group antigens

polymorphism

direct exclusion example

if the child exhibits a gene that neither the mother or alleged father has

indirect exclusion example

if a child lacks a genetic marker that the alleged father should have transmitted

Binding is very

specific, antibody reacts with only one epitope of an antigen

serology

the laboratory study of antigen-antibody reactions

most clinically significant antibodies that react at

antibody temperature are igG (most common)

valance

number of binding sites

Classical complement pathway is activated when

IgM or IgG (1 or 3) binds to antigen (igM only requires 1, IgG requires many)

bind complement and induce

ABO antibodies, intravascular hemolysis

clinically significant blood group antibodies can result in

extravascular hemolysis

Immunogenicity

degree to which an antigen is capable of electing an immune response

antigen characteristics influencing their immunogenicity

size, complexity, conformation, charge, accessibility, solubility, disgestibility, chemical composition

Polyclonal antibodies

secreted by different B cell lineages, they are a collection of immunoglobulin molecules that react against a specific antigen, each identifying a different epitope

monoclonal antibodies

made by identical B cells that are the clones of a unique parent cell using hybridoma technology, they have monovalent affinity, in that they all bind to the same epitope

what would likely be more optimal for laboratory testing?

monoclonal antisera

Naturally occuring antibodies

produced without transfusion, injection, or pregnancy (IgM, RT, or lower) activate complement

Immune antibodies

acquired through transfusion or pregnancy

Alloantibodies

directed at non-self antigens after exposure transfusion

Autoantibodies

Directed at self antigens, can have a specificity common to transfused blood or no detectable specificity

Most clinically significant RBC antibodies

react at body temp (37c)

The antibodies to ABO (IgM) are an important expection to

reacting at body temp

Detection of blood group antibodies depends on characteristics of

antigen-antibody reactions

The binding of an antigen and antibody is

a reversible process

Antigen-antibody reactions in vitro by visible _______ or evidence of

agglutination (antigen-antibody interaction), hemolysis

Two stages of a hemagglutination reaction

Sensitization and Lattice Formation

Sensitization

binding of antibody and antigen

Lattice Formation

cross-linking of antibody-coated RBCs resulting in visible agglutination of cells

Antigen-Antibody Ratio

The probability of antigen-antibody interaction relies upon the effect of the ratio of antibody and antigen concentrations (usually needing to add more antigen)

Postzone effect in an antigen-antibody reaction would likely result in

False-negative result

Dosage effect (in antigen-antibody ratio)

recall heterozygous genotypes can lead to weaker phenotype expression: less antigen binding present on RBC’s can lead to weaker antigen-antibody reactions

Factors influencing sensitization in antigen-antibody reactions

pH, temperature, incubation time, ionic strength

Factors influencing lattice formation in Antigen-antibody reactions

Distance between the cells (zeta potential), centrifugation, zone of equivalence (washing)

Zeta potential

red blood cells are negatively charged and the cations of the saline are attracted to it and form a stable cationic cloud around each cell causing a force of repulsion

IgM and IgG reaction to zeta potential

IgM is larger so agglutination can be seen without enhancement unlike IgG which is smaller and cannot overcome with enhancement

Whats an example that can enhance hemagglutinin reactions

increasing incubation time

To help detect IgG ______ or _______ are used to enhance the reactivity of IgG

potentiators or enhancement media

different potentiators

Low ionic strength solution (LISS), Polyethylene Glycol (PEG), Proteolytic Enzymes, Antihuman Globulin (AHG)

Low Ionic Strength Solution

decreases ionic strength of test system, reduces zeta potential, increases antibody uptake during sensitization and lowers it during incubation time

Polyethylene Glycol (PEG)

test system by removing water molecules, brings sensitized red cells closer together for lattice formation (more effective then LISS)

Proteolytic Enzymes

Enhances reactivity of Rh, Kidd, P1, Lewis and I blood but destroys of Fya, Fyb, M, N and S blood group

Antihuman Globulin (AHG)

Reveals if red cells are coated with antibody and/or complement proteins, only sensitize (bind) to them allowing for visible agglutination (useful since more sensitive)

Grading Hemagglutination: one large clump

4+ reaction

Grading Hemagglutination: few large chunks

3+ reaction

Grading Hemagglutination: still clear background, with many small chunks

2+ reaction

Grading Hemagglutination: turbid (free cells) background with many small chunks

1+ reaction

Grading Hemagglutination: pale red

Hemolysis (positive reaction)

Grading Hemagglutination: all red

negative reaction

Any hemolysis in Grading Hemagglutination is

positive result

what property of antibodies is not dependent on the structure of the heavy chain constant region

affinity for antigen

Has a valency of 10, shape is a pentamer, associated with intravascular cell destruction

IgM

found in mucosal linings

IgA

highest plasma/serum concentration, able to cross placenta, and detected with antiglobulin test

IgG

The majority of blood ground antibodies do not activate the classical complement pathway, but will still result in the clearance of antibody-coated cells via

extravascular hemolysis and monoculear phagocytic system

are in the plasma or serum

antibodies

are on the red cell membrane

antigen

an Rh(D)-negative mother gives birth to an Rh(D)-positive infant. what is most likely?

the mother might make anti-D due to exposure of the D antigen on baby’s RBCs during the pregnancy and/or delivery

3 things that can affect antibody agglutination

antibody-antigen ratio, temperature, pH

What term is used when red cells with the genotype MM react stronger with anti-M than red cells with the genotype MN? (M and N are an allele pair)

dosage effect

Reduces zeta potential between RBCs but does not decrease the required incubation time

Albumin

Reduces zeta potential by providing a low ionic strength environment, which increases antibody uptake and reduces the required incubation time

LISS

Increases test sensitivity; provides a low ionic strength environment while removing water molecules which concentrates the antibody in the test thereby facilitating atnibody cross-linking

PEG

Removes negative charges from the red cell membrane, which reduces zeta potential; denatures some red cell antigens

Enzymes

Cross-links IgG sensitized cells, producing visible agglutination

AHG