Forensic Serology

Chapter 10

Blood Components

Plasma—fluid part of unclotted blood

Erythrocytes—”red” cells that hold hemoglobin and transport oxygen

Leukocytes—immune “white” cells

Platelets—cell fragments that cause clotting

Serum—yellow fluid that remains after clotting of blood

Antigens and Antibodies

Antigen: A substance, usually a

protein, that causes an immune reaction in the body

Located on the outside of cells

Antibody Produced by body to

bind with specific antigens

One antibody per antigen

Antibodies are produced for foreign proteins

A, B, Rh (D) are antigens

Blood Types Blood Type A has A

antigens and B antibodies Blood Type B has B antigens

and A antibodies Blood Type AB has both A

and B antigens and no antibodies

Blood Type O does not have any antigens but both A and B antibodies

Rh+ blood has D antigens Rh- blood does not have

Rh(D) antigens but has D antibodies

Serology Rh+ blood will agglutinate

with Anti-D serum Rh- blood will not agglutinate

with Anti-D serum A blood will agglutinate with

Anti-A serum B blood will agglutinate with

Anti-B serum AB blood will agglutinate with

both anti-A and anti-B serum O blood will not agglutinate

with anti A or anti B http://

www.youtube.com/watch?v=E0d5Qx42vmQ

Immunoassay techniques

Used to detect drugs in blood and urine

Animals are injected with proteins with drug antigens—animal makes drug detecting antibodies that can be harvested

Presumptive drug testing with these cultured antibodies can be used to detect opiates, cannabinoids, cocaine, amphetamines, phencyclidine, barbituates and methodone

Producing Antibodies Radioimmunoassay (RIA)—uses

radioactive tags to find drugs Enzyme-Multiplied Immunoassay

Technique (EMIT)—fast and used with urine; adds antibodies to urine that bind to specific drugs

Polyclonal and Monoclonal Antibodies—animals produce many different kinds (polyclonal) of antibodies when exposed

Scientists need one kind of antibody (monoclonal)

Produce monoclonal antibodies using hybridoma cells (spleen cells fused with cancer cells)

Genetics of Blood Typing

Blood type is a genetic trait

Encoded in DNA DNA is grouped in

chromosomes Humans have 46

chromosomes: 23 from mother, 23 from father

Chromosomes contain genes

Alleles are versions of a gene

Genes can be dominant or recessive

Paternity Testing with Blood Type

Determined by 3 alleles: A, B, O

A Blood Type—AA or AO B Blood Type—BB or BO O Blood Type—OO AB Blood Type—AB Parent gives each

offspring one of two alleles

Genes of child must come from parents

Blood Stain Analysis

3 Questions Is it blood? Is it human? Can it be matched

closely to a particular person?

Presumptive Color Testing

Benzadine color test Detects presence of

hemoglobin Reduced use because

carcinogenic Kastle-Meyer—

Phenolphthalein indicator Turns pink when mixed

with hydrogen peroxide and catalase

Blood, horseradish, animal material all contain catalase

http://www.youtube.com/watch?v=6Ex0Fd_PDhU

Luminol

Presumptive blood test Reaction with blood

emits light Spray on suspected

area, turn out lights, see blue light

http://www.youtube.com/watch?v=hbEHvRrfqrc

Microcrystalline Tests

Oldest method of blood detection

Takayama test Teichmann tests Add chemicals to blood

that causes crystals to form with hemoglobin

Susceptible to interference from contaminants

Less sensitive than color tests

Precipitin Test Used to determine if blood

stain is human or animal Inject human blood into

rabbit to produce antibodies

Create human antiserum from rabbit blood

Human antiserum reacts with human blood to produce precipitate

Can also create dog, horse, other animal antiserum

Gel Diffusion with Precipitin

Use agar gel Blood and human

antiserum are loaded into wells

Antibodies and antigens come together in medium plate

Precipitate forms between two wells if blood is human

Electrophoretic method uses electric field to speed up the process

Blood Spatter Important Blood Qualities to

Interpret Blood Spatter Surface texture—more

spatter with softer porous material

Direction of travel—pointed end faces direction of travel

Impact angle—right angle yields circular stain

Origin of spatter—draw lines through many spatter points; point of intersection is origin of spatter

http://www.youtube.com/watch?v=Od8YuwUT794

Forensic Analysis of Semen

Tests for Presence of Semen Acid Phosphatase Test

acid phosphatase is an enzyme made by the prostate gland

400x more concentrated in semen acidic sodium alpha napthylphosphate +

fast blue dye + acid phosphatase = turns purple

4-methyl umbelliferyl phosphate + acid phosphatase = fluoresces in UV light

Microscopic examination Dissolve stain in water Look for presence of sperm cells

Prostate specific antigen Grow polyclonal antibodies to PSA in

rabbits Gel electrophoresis Use monoclonal antibodies with dye

Rape Evidence Collection

Rape Kit Collection from victims Hair samples: head,

pubic, body Body opening swabs:

vagina, anus, mouth (as needed)

Dry skin swabs (as needed)

Blood sample Fingernail scrapings All clothing (store in

paper) Urine sample

Collected from male suspects All clothing Hair: head, pubic, and

body Genital swab Blood sample Cheek cells