Chapter 8 FORENSIC SEROLOGY

Nature of Blood The word blood refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances. Plasma, which is the fluid portion of blood, is composed principally of water. Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are the solid materials suspended in plasma. Antigens, usually proteins, are located on the surface of red blood cells and are responsible for blood-type characteristics.

What makes up our blood? RED BLOOD CELLS (erythrocytes) – The most abundant cells in our blood; they are produced in the bone marrow and contain a protein called hemoglobin that carries oxygen to our cells. WHITE BLOOD CELLS (leukocytes) – They are part of the immune system and destroy infectious agents called pathogens. PLASMA – The yellowish liquid portion of blood that contains electrolytes, nutrients and vitamins, hormones, clotting factors, and proteins such as antibodies to fight infection. PLATELETS (thrombocytes) – The clotting factors that are carried in the plasma; they clot together in a process called coagulation to seal a wound and prevent a loss of blood.

AA or AO = Type A BB or BO = Type B OO = Type O AB = Type AB What are blood types? There are 3 alleles or genes for blood type: A, B, & O. Since we have 2 genes, there are 6 possible combinations. Blood Types AA or AO = Type A BB or BO = Type B OO = Type O AB = Type AB http://learn.genetics.utah.edu/units/basics/blood/types.cfm

Rh Factors A+ A- B+ B- AB+ AB- O+ O- Referred to as the “Rh Factor” after the Rhesus monkey. Scientists study Rhesus monkeys to learn more about the human anatomy because there are certain similarities between the two species. While studying Rhesus monkeys, a certain blood protein, that is also present in some human blood, was discovered. The presence of the protein, or lack of it, is referred to as the Rh (for Rhesus) factor. If your blood does contain the protein, your blood is said to be Rh positive (Rh+). If your blood does not contain the protein, your blood is said to be Rh negative (Rh-). A+ A- B+ B- AB+ AB- O+ O- http://www.fi.edu/biosci/blood/rh.html

Blood Typing More than 15 blood antigen systems have been identified, but the A-B-O and Rh systems are the most important. An individual that is type A has A antigens on his/her red blood cells, type B has B antigens, AB has both A and B antigens, and type O has neither A nor B antigens. Rh factor is determined by the presence of another antigen, the D antigen. People having the D antigen are Rh positive; those not having the antigen are Rh negative. For every antigen there is a specific antibody that will react with it to form clumps known as agglutination. Thus, if serum containing anti-B is added to red blood cells carrying B antigen, they will immediately react.

ABO and Rh Factors Blood Type Can Donate to Can Receive from A+ A- B+

Anti-Sera An animal, such as a rabbit or mouse, is injected with an antigen Its body will produce a series of different antibodies, designed to attack the antigen of interest. This collection of antibodies is known as polyclonal antibodies. A more uniform and specific collection of antibodies can be manufactured. Designed to attack a single antigen site Such antibodies are known as monoclonal antibodies.

Blood Typing Antigens – proteins found on Red Blood Cells Antibodies – proteins attack foreign substances Agglutination – clumping – antibody fights antigen Anti-A Sera – “fights” A antigens Anti-B Sera – “fights” B antigens A Blood – Positive Anti-A, Negative Anti-B B Blood – Negative Anti-A, Positive Anti-B AB Blood – Positive Anti-A, Positive Anti-B O Blood – Negative Anti-A, Negative Anti-B + Blood – Positive Anti-Rh or Anti-D - Blood – Negative Anti-Rh or Anti-D

Heredity and Paternity The transmission of hereditary material is accomplished by means of microscopic units called genes, located on chromosomes. Alternative forms of genes that influence a given characteristic (such as eye color or blood type) are known as alleles. Paternity testing has historically involved the A-B-O blood typing system, along with blood factors other than A-B-O. Currently, paternity testing has implemented DNA test procedures that can raise the odds of establishing paternity beyond 99 percent.

Serology The term serology is used to describe a broad scope of laboratory tests that use specific antigen and serum antibody reactions. The identity of each of the four A-B-O blood groups can be established by testing the blood with anti-A and anti-B sera.

How can blood be used as evidence? Blood samples – Can be analyzed to determine BLOOD TYPE and DNA, which can be matched to possible suspects. Blood droplets – Can be analyzed to give clues to the location of a WOUND, movement of a VICTIM, and type of INJURY. Blood spatter – Can be analyzed to determine PATTERNS that give investigators clues to how a crime might have happened.

Forensics of Blood The criminalist must be prepared to answer the following questions when examining (an unknown stain that could be) dried blood: 1. Is it blood? 2. From what species did the blood originate? 3. If the blood is of human origin, how closely can it be associated to a particular individual? The determination of blood is best made by means of a preliminary color test.

The Tests A positive result from the Kastle-Meyer color test is highly indicative of blood. Hemoglobin causes a deep pink color. Alternatively, the luminol test is used to search out trace amounts of blood located at crime scenes. Produces light (luminescence) in a darkened area. Microcrystalline tests, such as the Takayama and Teichmann tests, depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed.

The Tests Once a stain has been characterized as blood, the precipitin test will determine whether the stain is of human or animal origin. Uses antisera normally derived from rabbits that have been injected with the blood of a known animal to determine the species origin of a questioned bloodstain. Once it has been determined that the bloodstain is of human origin, an effort must be made to associate or dissociate the stain with a particular individual. DNA analysis has allowed forensic scientists to associate blood to a single individual.