Chapter 8 FORENSIC SEROLOGY 8-1
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. 8-2
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. 8-3
ABO Blood Groups Plasma Plasma Plasma Plasma 8-4
No Agglutination Reaction A person with blood type A can receive blood from a donor with blood type A. The anti-b antibodies in the recipient do not combine with the type A antigens on the red blood cells of the donor. 8-5
Agglutination Reaction A person with blood type B cannot receive blood from a donor with blood type A. The anti-a antibodies in the recipient will combine with the type B antigens on the red blood cells of the donor. 8-6
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A blood transfusion is a procedure in which blood is given to a patient through an intravenous (IV) line in one of the blood vessels. Blood transfusions are done to replace blood lost during surgery or a serious injury. A transfusion also may be done if a person s body can't make blood properly because of an illness. Who can give you blood? People with TYPE O blood are called Universal Donors, because they can give blood to any blood type. People with TYPE AB blood are called Universal Recipients, because they can receive any blood type. Universal Donor Rh + Can receive + or - Rh - Can only receive - Universal Recipient 8-8
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. The concept of specific antigen antibody reactions has been applied to immunoassay techniques for the detection of drugs of abuse in blood and urine. 8-9
Immunoassay A number of immunological assay techniques are commercially available for detecting drugs through antigen-antibody reaction. One such technique, the enzyme-multiplied immunoassay technique (EMIT), is used by toxicologists because of its speed and high sensitivity for detecting drugs in urine. In a typical EMIT analysis, antibodies that will bind to a specific drug are added to the subject s urine. Other immunoassay procedures are also available, such as radioimmunoassay (RIA), which uses drugs labeled with radioactive tags. 8-10
Figure 8 3 Stimulating production of drug antibodies. 8-11
In the EMIT assay, a drug that may be present in a urine specimen will compete with added labeled drug for a limited number of antibody binding sites. The labeled drugs are indicated by an asterisk. Once the competition for antibody sites is completed, the number of remaining unbound labeled drug is proportional to the drug s concentration in urine. 8-12
Antigen-Antibody Reaction When an animal, such as a rabbit or mouse, is injected with an antigen its body will produce a series of different antibodies, all of which are designed to attack some particular site on the antigen of interest. This collection of antibodies is known as polyclonal antibodies. Alternately, a more uniform and specific collection of antibodies designed to combine with a single antigen site can be manufactured. Such antibodies are known as monoclonals. 8-13
Steps required to produce monoclonal antibodies. 8-14