Transcript Serology

Serology
Study of bodily fluids using
antigen-antibody reactions
Blood Components
RBC – Erythrocytes
 WBC – Leukocytes
 Platelets – Contains fibrin which clots
blood
 Plasma – Fluid portion of the un-clotted
blood
 Serum – Fluid that is separated from
clotted blood

Antigen – Antibody Reactions
Antigens- proteins on surface of cells
 Antibodies- proteins that are produced in
response to the presence of foreign
antigens (Found in the serum of blood)
 Agglutination- reaction that occurs
when specific antibodies attach to antigen
sites and cause RBC to clump together

 >15
blood antigen systems have been
identified, including A-B-O and Rh systems
( Saferstein, 2004, pg 330)
What Makes Blood Different?
Agglutination
ABO System
Blood Type
Antigens/RBC
Antibodies/Serum
A
A
Anti-B
B
B
Anti-A
AB
AB
Neither anti-A or B
O
Neither A nor B
Both anti-A and B
Blood Typing
Anti-A
serum +
blood
+
Anti-B
Serum +
blood
_
_
+
+
+
_
_
Antigen
Present
Blood Type
Immunoassay Techniques

Antigen-Antibody reactions used for the
detection of Drugs in blood, urine and
semen
 EMIT
: Enzyme-Multiplied Immunoassay
Technique – are not totally specific
 Monoclonal Antibody Tests: antibodies are
produced to react to ONE specific antigen
 Currently
found in newest forensic test kits
(pg333-335)
Standard Analysis of Blood

Questions about crime scene blood:
 Is
the substance blood?
 Is the blood human?
 Can the blood be associated with a
particular individual?
Is the substance blood?

Kastle-Meyer Color Test
 Phenolphthalein,
hydrogen peroxide, and
suspected blood stain are mixed; positive
reaction indicated by a deep pink color
 Based
upon observation that hemoglobin
possesses peroxidase activity
 This test is a presumptive or preliminary test for
blood.
 Substances other than blood may produce false
positive results (pg 336)
Is the substance blood? Con’t

Hemastix Color Test
 Hemastix—has
been found to be very useful
by field investigators—a dipstick moistened
with distilled water is placed in contact with
the suspect blood—a green color change
indicates a positive result (pg 336)
Is the substance blood? Con’t

Luminol Test
A
test that produces light when it reacts with
blood rather than color
 Large areas can be quickly screened for
blood, by spraying luminol reagent
 “Luminol test is extremely sensitive—it is
capable of detecting blood stains that have
been diluted up to 300,000 times.”
 Does not interfere with subsequent DNA
testing! (pgs 336-337)
Is the blood human?

Precipitin Test
 If
you inject an animal with human blood, the
animal will create antibodies that can then be
recovered and used to test for various human
antigens including human blood antigens
 The recovered antibodies are called human
antiserum
 To
test for human blood, human antiserum
and an unknown blood are put together—if
the blood is human a precipitate will form.
(p338)
Can the blood be associated with
a particular individual?

A-B-O types and enzymes



Used until the mid 1990’s, characterization of
bloodstains included determining A-B-O types and
polymorphic enzyme markers such as PGM
(phosphoglucomutase)
These tests added statistical information with which
to reduce the number of possible sources of the
bloodstain
Because antigens, and enzymes occur independently
of one another, the probability of a dried blood stain
having a particular combination of these factors is
determined by the product of their distribution in the
population (pg 339)
Can the blood be associated with a
particular individual? Con’t

Statistical Example:
 Blood
stain found to be of type A—
corresponds to 42% percent of population
 Stain contains PGM-1—corresponds to 58% of
population
 The
combined effect of just these two factors,
using the product rule is 42% x 58% or 24 %
 Clearly the more factors, the smaller the frequency
of occurrence in the population
Can the blood be associated with a
particular individual? Cont….

DNA Analysis
 Since
the 1990’s DNA analysis has replaced
forensic reliance on blood factors for the
routine characterization of bloodstains
 DNA analysis gives extremely accurate
individualization results.
Stain Patterns of Blood

The location, distribution and appearance
of bloodstains and spatters can be used to
interpret and reconstruct the events that
must have occurred to produce the
bleeding. (pg. 342)
Stain Pattern Analysis
General Conclusions
Surface texture: The harder and less
porous the surface, the less spatter
results.
 Direction of Travel: The direction of travel
of blood can be discerned by the stain’s
shape — the pointed end always faces its

direction of travel
(pg 342)
Stain Pattern Analysis
General Conclusions Cont…
Impact Angle: A drop of blood striking a
surface at a right angle gives rise to a nearly
circular stain; as the angle decreases, the stain
becomes more elongated in shape
 Origin of Blood Spatter: Can be determined
by establishing lines through the long axis of
several individual blood stains. The intersection
of the lines represents the point from which the
blood emanated. (pg 342)
 http://www.bloodspatter.com/BPATutorial.htm

Principles of Heredity
The gene is the basic unit of heredity.
They found on chromosomes. All human
cells contain 46 chromosomes (23 pairs).
Only exception: reproductive cells
 During fertilization, a sperm and egg
combine so each contributes
chromosomes to form the new cell
(zygote)

Principles of Heredity Cont..

Inheritance Rules
A
gene pair of two similar genes—is
homozygous—no problem determining a
person’s outward characteristics
 A gene pair of two different genes—is
heterozygous—one gene is dominant, the
other recessive—person’s outward
characteristics depend on the dominant gene
Paternity Testing
Many cases of disputed paternity can be
resolved when suspected parents and
offspring are related according to their
blood group systems
 Type O blood is considered a recessive
gene so……

Paternity Example
Father’s Genotype
Mother’s
O
O
A
AO
AO
B
BO
BO
Genotype
If
the Child in question is type AB would the suspect
father be cleared?
Paternity Testing Con’t
Routine paternity testing involves
characterizing many blood factors other
than A-B-O. Using these other factors the
probability of establishing paternity
becomes better than 90%. Once DNA
analysis is done the odds become better
than 99%. (pg 348)
Forensic Characterization of
Semen


A large number of cases involve sexual
offenses, making it necessary to examine
exhibits for the presence of seminal stains.
The forensic examination of semen is a twostep process:
1.
2.
Semen must be located
Tests must be performed to prove its identity—it
may even be tested for blood type

Note: Semen is checked for blood type because many
individuals are secretors
Secretors
80% of individuals are classified as secretors
 This means that their blood-type antigens are
also found in high concentrations in most body
fluids
 Ex- Saliva, semen, vaginal secretions, and
gastric juices
 **Saliva & semen have higher concentrations of
A & B antigens than blood!!

Semen Location and
Identification

There are two methods of locating
semen:
Semen is often readily visible on a fabric
because it has a stiff crusty appearanceunreliable
2. The acid phosphatase color test can locate
and at the same time identify semen.
1.
Acid Phosphatase Color Test
Acid phosphatase is an enzyme secreted
by the prostate gland into seminal fluid
that is in far greater concentrations than
those found in any other body fluids.
 Its presence can be detected using
different tests:

 1.
Contact with a special acidic solution and
Fast Blue B dye shows a purple change
 2. Contact with a solution of MUP fluoresces
under UV light. (p.349)
Acid Phosphatase Test, Con’t
Large areas or fabrics can be quickly searched
by moistening filter paper with the detector
solutions and rubbing over the suspect area
 Some substances will give a false-positive result
(fruit juice, contraceptive creams, etc), but none
of these substances will react with the speed of
seminal fluid.


Note: A reaction of less than 30 seconds is a strong
indication of semen. (p 349)
Microscopic Examination of
Semen
Rapid stirring of a fabric-stain-water
mixture will transfer a small amount of
sperm into the water. A drop is then
taken, dried, stained and looked at under
the microscope.
 The presence of sperm indicates the
presence of semen.

Microscopic Problems

Locating sperm with the microscope is not that
easy for three reasons:


1. Sperm are very brittle when dried and easily
disintegrate. They are also hard to remove from cloth
material.
2. Sexual crimes may involve males who have an
abnormally low sperm count, condition called
oligospermia.

3. Males who have no sperm in their seminal fluid,
condition called aspermia—often due to increasing
numbers of vasectomies.
Detecting Semen, Cont…

A positive result for acid phosphatase and
a negative result for semen give
ambiguous results—In this case, p-30 or
Prostate Specific Antigen (PSA) is used to
detect seminal plasma – Immunoassay
tests
p30 Prostate Specific Antigen
Test

Formation of a visible line between the
wells of anti p-30 and semen extract–
proves the stain is seminal
Collection of Rape Evidence
Victim
Outer and undergarments are placed in separate
paper bags, while victim stands on a piece of
paper. The paper is then folded and collected.
 Bedding or the object upon which assault took
place should be submitted to the lab.
 Rape victim must be subjected to a medical
examination Collected items include pubic hairs,
vaginal swabs, blood, fingernail scrapings,
clothing and urine (p 352)

Rape Suspect

Suspect must also undergo an exam.
Routine items collected include clothing,
hairs, penile swab and blood samples
Timeline
Living or motile sperm may survive 4 to
six hours in the vagina of a living person.
 Non-motile sperm may be found in a living
female for up to three days and
occasionally up to six days
 Intact sperm (sperm with tails) are not
normally found 16 hours but have been
found as late as 72 hours after
intercourse.

Important Considerations Based
Upon Timeline
How long ago was the person raped?
 When did voluntary sexual activity last
occur prior to the sexual assault?

 Blood
is taken from any consensual partner
having sex with the victim within 72 hours of
the assault.
What are these?