Serology (Forensic Science)
In forensic science, serology is typically used to identify biological evidence related to crimes such as sexual or physical assault, homicide, kidnapping, and robbery. Contact between victims and offenders as well as between people and objects during crimes can lead to the transfer of biological materials, as noted by Locard’s exchange principle. Serological evidence may prove or disprove statements by suspects, victims, or witnesses and may associate evidence with suspects or victims. The types of biological evidence most often subjected to serological analysis include the biological fluids blood, saliva, and semen.
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Composition and Markers of Biological Fluids (Forensic Science)
Different types of biological evidence analyzed by serology have distinctive cellular and molecular compositions. Blood contains cells as well as both biological and inorganic molecules and ions. Blood cells are divided into two major groups: red blood cells (erythrocytes), which are major sources of blood group antigens but contain no DNA (deoxyribonucleic acid), and white blood cells, which contain DNA and B-lymphocyte subpopulations that produce antibodies that are widely used tools in serology.
Hemoglobin is a substance specific to red blood cells and absent from other body cells. Reactivity with hemoglobin forms the basis of most forensic tests for blood. Blood contains a great variety of proteins, some of which display inherited variations in structure and therefore were historically used in forensic serology to exclude or associate bloodstains with individuals before the rise of DNA typing. Certain of these proteins are also found in other biological fluids.
Spermatozoa are a unique cellular component used to identify semen in biological evidence. Spermatozoa exhibit unique morphology in that each has a compact region or “head” containing most of the organelles, a short cylindrical region or midpiece, and an elongated whiplike appendage or “tail.” Proteins specific for semen include prostate-specific antigen(PSA) and semenogelin. Certain other biological molecules, however,...
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Tests for Biological Fluids (Forensic Science)
Most tests for the detection and identification of blood are based on reactions with hemoglobin from erythrocytes. Several screening tests are color tests that rely on the ability of hemoglobin to transfer oxygen from hydrogen peroxide to another substance that either changes color (for example, pink for phenolphthalein, green for tetramethylbenzidine) or causes the production of light (chemiluminescence), as in the case of luminol. To identify stain material as blood conclusively after one of these presumptive tests, a forensic scientist may perform a microcrystalline test. In such a test, a trace scraping of the stain is gently heated with particular chemicals; if blood is present, microscopic examination will reveal the formation of crystals of characteristic shapes and sizes.
Immunology-based methods are used to identify the species of origin of bloodstains. Some methods, such as lateral-flow immunoassay, use monoclonal antibodies against human hemoglobin to identify human blood. Another method uses immunoprecipitation of human blood proteins by antibodies against human blood (serum) proteins on extracts of the stain evidence in an agarose medium.
A presumptive test for semen relies on detection of the enzyme acid phosphatase, which is more abundant in semen than in other biological fluids. One confirmatory test for semen involves microscopic examination of material after treatment with the “Christmas...
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Blood Group Typing (Forensic Science)
Human blood groups were the first genetically based systems used by forensic scientists to gain information on who might or might not be the sources of biological evidence. Identification of blood groups from evidence samples involves the use of defined antibodies to agglutinate (clump together) erythrocytes based on the type of inherited blood group carbohydrates on the erythrocyte. ABO and Rh blood group antigens are the major systems used. Several other types of blood groups (such as Lewis and MN antigens), involving other genetically inherited structures, have been used in forensic serology. Blood group typing of dried bloodstains and other body fluids is achieved through various methods of extracting stains and testing the extracts for their ability to inhibit agglutination.
Inherited differences (polymorphisms) exist in proteins found in blood and other biological fluids. By using serological techniques to identify which variants of proteins are present in biological evidence, scientists can help to associate victims or suspects with particular items of evidence or exclude victims or suspects from consideration. Electrophoretic analyses identify protein variants based on the differing degrees to which they move in an electric field while in a medium such as agarose or polyacrylamide. Some polymorphic blood proteins include transferrin, Gc (group-specific component), phosphoglucomutase, and haptoglobin. Better testing...
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Further Reading (Forensic Science)
Baechtel, F. S. “The Identification and Individualization of Semen Stains.” In Forensic Science Handbook, edited by Richard Saferstein. Vol. 2. Englewood Cliffs, N.J.: Prentice Hall, 1988. Discusses semen identification and the use of classical serological techniques for analyzing whether a semen stain originated from a given person.
Gaensslen, R. E. Sourcebook in Forensic Serology, Immunology, and Biochemistry. Washington, D.C.: National Institute of Justice, 1983. Presents a comprehensive review of the fundamentals and practice of forensic serology.
Houck, Max M., and Jay A. Siegel. Fundamentals of Forensic Science. Burlington, Mass.: Elsevier Academic Press, 2006. Good general textbook includes a chapter that succinctly describes the field of forensic serology and its relevance.
Nash, Jay Robert. Forensic Serology. New York: Chelsea House, 2006. Provides background information on the use of serology in the forensic sciences and discusses various techniques of forensic serology.
Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. 9th ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2007. Introductory textbook includes a chapter that covers immunology basics and the history and methods of forensic serology.
Whitehead, P. H. “A Historical Review of the Characterization of Blood and Secretion Stains in the Forensic...
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Science and Profession (Magill’s Medical Guide, Sixth Edition)
The term “serology” comes from the Latin sero (serum, a blood liquid) and ology (the study of). Many serologic testing procedures have been developed to determine the amounts of specific antibodies the individual has circulating in his or her bloodstream. These tests can help the physician diagnose disease conditions and develop appropriate treatment regimens. To understand serological testing in relation to blood typing and immunity—two major uses of serology—it is necessary to understand the structure and nature of blood cells and the workings of the human immune system.
The surface of red blood cells contains antigenic determinants that define the individual’s blood group. There are more than twenty blood grouping systems; the most common, the ABO system, identifies individuals as being in A, B, AB, or O groups, depending on the antigenic determinant present on their red blood cells. The red blood cells of people in the A group are covered with A antigen, in the B group with B antigen, and in the AB group with both antigens. Red blood cells in the O group have neither A nor B antigens. The antigenic determinant causes the body to produce antibodies against other blood types. For example, if an individual’s red blood cells are coated with A antigen, the body will produce antibodies against B antigen. Therefore, if a person with A blood is given B blood cells, these cells will be regarded...
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Diagnostic and Treatment Techniques (Magill’s Medical Guide, Sixth Edition)
The major use for seronegative-seropositive testing is in blood typing. The patient’s blood type is recorded as part of his or her medical history and is required for a blood transfusion to ensure that the patient receives blood from a compatible donor. Blood typing is an activity conducted in, or readily available to, virtually every medical facility. A major example is the Coomb’s test, which detects antibodies on red blood cells in the bloodstream and establishes whether the patient has sensitized cells. This information is helpful in cross-matching donor and patient blood and in the diagnosis of hemolytic anemia.
Another important aspect of serologic testing is to determine the immune status of an individual—that is, whether a person or a local population is immune to a specific disease or is susceptible and therefore should be vaccinated. Such tests are geared to the identification of antibodies that protect against certain diseases. These antibodies are created by exposure to the disease-causing microorganism as a result of infection by the organism itself; vaccination, in which a modified form of the microorganism is used to trigger the body’s immune response; or immunity that is acquired by a newborn baby from a mother, an immune state that lasts only a few months. A test that comes back seronegative or with very low antibody levels indicates that the patient is not immune to a given...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The science of serology and serological testing for antibodies and antigens in the body have become mainstays of modern medical diagnosis and treatment for a wide range of diseases. Virtually every individual in the industrialized world and most members of the developing world urban populations undergo serologic testing as part of their regular medical routine.
Serological testing is part of every hospital workup, almost every routine medical examination, every blood transfusion, all transplant procedures, many diagnostic procedures, and many treatment regimens. It is the basis for most epidemiological studies that enumerate the extent of susceptibility to individual diseases in various populations and hence directs the development of immunization programs. It is an integral part of vaccine production and is critical in the development of new vaccines. With the development of monoclonal antibody research, serology enters a new era where the possibilities of improved serologic testing and therapeutic modalities seem almost unlimited.
Serological testing and therapy, so far, have been based on the manipulation and modification of living organisms. It is theoretically possible to develop vaccines and therapeutic agents that are completely synthetic in structure. This science promises greater specificity and efficacy, both for vaccines and for disease treatment.
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Bryant, Neville J. An Introduction to Immunohematology. 3d ed. Philadelphia: W. B. Saunders, 1994. This book was written as a background text for laboratory personnel and students. Somewhat technical, but the writing is clear and the author covers the subject well.
Chase, Allan. Magic Shots. New York: William Morrow, 1982. An excellent history of immunization that covers ancient medical practice and describes the work of such early pioneers as Edward Jenner and Louis Pasteur. Details the major discoveries that have taken place in the twentieth century, such as the development of the polio vaccine and the eradication of smallpox.
Griffith, H. Winter. Complete Guide to Medical Tests. Tucson, Ariz.: Fisher Books, 1988. A complete compendium of all tests used in hospitals and other medical facilities. All current seronegative-seropositive tests are described and categorized according to their diagnostic and therapeutic uses.
_______. Complete Guide to Symptoms, Illness, and Surgery. Revised and updated by Stephen Moore and Kenneth Yoder. Rev. 4th ed. New York: Perigee, 2000. Covers more than five hundred diseases and disorders and includes information about diagnostic tests that involve serology.
Litin, Scott C., ed. Mayo Clinic Family Health Book. 4th ed. New York: HarperResource, 2009. A superior medical reference for the general reader which gives a...
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Serology (World of Microbiology and Immunology)
Serology is the study of antigen-antibody reactions outside of a living organism (i.e., in vitro, in a laboratory setting). The basis of serology is the recognition of an antigen by immune mechanisms, with the subsequent production of an antibody.
In medical terminology, serology refers to a blood test to detect the presence of antibodies against a microorganism. The detection of antibodies can be qualitative (i.e., determining whether the antibodies are present) or quantitative (i.e., determining the quantity of an antibody produced). Some microorganisms can stimulate the production of antibodies that persist in a person's blood for a long time. Thus, in a qualitative assay the detection of a particular antibody does not mean that the person has a current infection. However, it does mean that it is likely that at some time that person was infected with the particular microbial pathogen. Serology assays can be performed at various times and the level of antibody determined. If the antibody level rises, it usually is indicative of a response to an infection. The body produces elevated amounts of the antibody to help fight the challenging antigen.
Serology as a science began in 1901. Austrian American immunologist Karl Landsteiner (1868943) identified groups of red blood cells as A, B, and O. From that discovery came the recognition that cells of all types, including blood cells, cells of the body, and microorganisms carry proteins and other molecules on their surface that are recognized by cells of the immune system. There can be many different antigens on the surface of a microorganism, with many different antibodies being produced.
When the antigen and the antibody are in suspension together, they react together. The reaction can be a visible one, such as the formation of a precipitate made up of a complex of the antigen and the antibody. Other serology techniques are agglutination, complement-fixation and the detection of an antigen by the use of antibodies that have been complexed with a fluorescent compound.
Serological techniques are used in basic research, for example, to decipher the response of immune systems and to detect the presence of a specific target molecule. In the clinical setting, serology is used to confirm infections and to type the blood from a patient. Serology has also proven to be very useful in the area of forensics, where blood typing can be vital to establishing the guilt or innocence of a suspect, or the identity of a victim.
See also Antibody and antigen; Antibody formation and kinetics; Antibody-antigen, biochemical and molecular reactions; Bacteria and bacterial infection; Immune system; Laboratory techniques in immunology
Serology (World of Forensic Science)
Serology testing (assay) is largely used by forensic laboratories to analyze blood samples from suspects and bloodstains collected at the crime scene, in order to identify blood types of victims and assailants. The main objective of forensic tests, whether serological or other types, is to individualize samples through the identification of their sources.
Blood is the most common physical evidence in accidents, murder cases, and violent crime investigations. Besides blood, crime scene technicians may also find other stains and residues similar to blood in appearance at the scene, such as tomato sauce, red paint, or animal blood. To identify human blood, forensic scientists test samples at the crime scene with the chemical phenolphthalein, in an assay known as the Kastle-Meyer color test. Phenolphthalein releases hydrogen peroxide that reacts with an enzyme known as catalase in the blood. Catalase breaks down the hydrogen peroxide into water and oxygen, therefore releasing bubbles. However, as vegetables, animals, and some bacteria also produce catalase, this test only rules out the inorganic samples. Organic (plant or animal derived) samples are then collected for further serological analysis at the crime laboratory.
Body fluids such as blood, semen, saliva, and sweat, all contain serum. Serum is a liquid component of blood composed of water, trace minerals, several proteins including albumin, and immunoglobulins or antibodies. Albumin is the sticky protein that gives blood enough density for the water within it to remain inside the walls of arteries and veins. (Egg white contains high levels of albumin, which gives it the characteristic consistency.) When red and white blood cells are removed from blood, the resulting clear golden yellowish liquid is serum. Serology is therefore the study of the properties of serum. Serological tests have a wide range of applications in medicine, such as immunology and allergy assays, infection diagnosis, and blood typing. Serology can determine whether an individual was exposed in the past or if he is presently infected with a variety of pathogens (disease-causing organisms), such as hepatitis, measles, anthrax, syphilis, or HIV. Serology tests can also determine the presence of alcohol, illegal drugs, and poisons in the serum. Serological tests are also used in forensics to identify blood ABO groups, whose results, although not conclusive, may help to exclude or include suspects in the investigation process. If for instance, a suspect is blood type B and the samples from the crime scene are all types A and O, the suspect with type B blood can be excluded from the investigation.
Serology is such a convenient diagnostic tool because the immune system produces specific molecular tags in the blood for practically each foreign substance or invading microorganism. Each one specializes in binding to a specific molecule such as a viral, parasite, or bacterial protein, as well as to foreign substances such as poisons and drugs. For minutely small drug molecules against which the immune system is not very sensitive, special immune reagents were developed for the detection of drug abuse. An example is the Homogeneous Enzyme Immunoassays (EMIT), which is commercialized in kits ready for use.
To determine whether a blood sample is from a human or animal source, samples are tested with anti-human serum. This method was discovered by the German biologist Paul Uhlenhunth in the late 1870s. He injected protein from a chicken egg into a sample of rabbit's blood. After a few days, he extracted the rabbit's serum and mixed it with egg white, causing the separation of egg proteins from the solution to form a whitish clotting substance, precipitin. Precipitin is now a generic name for the resulting agglutinated complex formed when antibodies present in the serum of a species agglutinate the proteins in the blood of a different species. The forensic test consists of collecting the blood sample in a test tube containing serum from a rabbit containing antibodies against human blood, known as anti-human antibodies. If an insoluble complex of precipitin (clumping) occurs, the test is positive for human blood. This test can also be conducted using gel-electrophoresis, when a blood sample is put on a glass slide and covered by a layer of agar gel. The slide is positioned side by side with another containing the rabbit anti-human serum, inside a box filled with a solution that conducts electric current. As the current passes through, protein molecules are filtered into the gel and toward each glass slide. If precipitin is formed, the test is positive, and the blood sample is identified as human blood.
Electrophoresis is also used in typing the different groups of human blood, known as the ABO grouping system. After the discovery of antibodies and antigens (molecules to which antibodies bind), scientists identified four blood types among humans between 1875 and 1901. All human blood contains antigens in red cells that vary in type among individuals in accordance with inheritance (e.g., maternal and paternal inherited genes). Genes A and B (chromosome 9) encode enzymes that add specific sugars to an antigen at the ends of a complex sugar molecule (polysaccharide) that is present on the surface of erythrocytes (red blood cells). Individuals who inherit neither A or B genes have type O blood. As genes A and B are codominant (they do not dominate each other), individuals who inherit both genes (one from each parent) are type AB. The following other inherited combinations may occur: AA, BB, AO, BO, OO. Individuals AO or BO are respectively heterozygous type A and type B. AA or BB are homozygous types A or B.
Blood typing tests consist of mixing blood samples with anti-serum A on one side of the slide, and with anti-serum B at the other side. If the agglutination (clumping) occurs on both sides of the glass slide, the blood is AB. If it occurs only with anti-serum A, the blood is type A, or if it occurs only with anti-serum B, the blood is type B. If no agglutination occurs, the blood is type O. Because a person with type O blood does not present antigens to either A or B antibodies, they can donate blood to most blood groups. Carriers of gene A that have antibodies against B antigens in their blood plasma, and vice versa, can only receive transfusions of the same blood type or from type O blood. Individuals with AB blood type can receive transfusions from all donors. Type O carriers however cannot receive blood from the other types because their plasma contains antibodies against A and B antigens.
Population prevalence of blood types is approximately as follows: type A is more common in Caucasians and Europeans; type B among Africans, African descendents, and South Asia populations; AB type is predominant in China, Japan, and Korea; and Type O is predominant in Native Americans, Aborigines, and Latin American populations, and is common in Middle-Eastern populations as well. A small portion of the world population carries a rare variation of AB type subgroups that present weak reactions or no reaction at all to antibodies.
Another breakthrough of significance for both medical and forensic sciences was the discovery by Karl Landsteiner in 1940 that 85% of the human population carries erythrocytes that express the Rh(D) antigen, or Rhesus disease antigen (a protein also present in Rhesus monkeys). Blood is designated as being either Rh positive (+) or Rh negative (-). If an Rh- person receives blood from a donor who is Rh+, his immune system will develop antibodies against the antigen, causing disease or death, depending on the quantity of blood transfused. There are thirty possible combinations between ABO groups and Rh factors. Approximately two thirds of all people have an O+ or A+ blood type, with all other types comprising the remaining third. These variations allow the number of suspects in a crime investigation to be narrowed.
Another singular characteristic of proteins and enzymes is the presence of discrete variations in a single base pair of the genes that encode them, known as polymorphisms (or multiple forms of the same gene). More than 1% of any given population has polymorphisms in specific genes. Specific polymorphisms are also more prevalent in certain populations. For instance, the CYP enzymes of the gene Cytochrome P 450 show a specific polymorphed version in 40% of the Asian population, whereas another polymorph is more prevalent among Caucasians and Europeans. Several other enzymes also present a known prevalence among races, and are therefore, useful in forensic testing.
Genetic screening for polymorphisms in forensic samples is very helpful when combined with blood type and Rh factors, because it sharply reduces the probability the existence of two persons with the same blood characteristics being involved with the same crime to very insignificant odds. In addition, other serological tests can also be used to estimate age, sex, and race of suspects, such as hormonal levels in blood and other fluids, as well as genetic analysis such as chromosomal typing (or karyotyping), and DNA profiling.
SEE ALSO Animal evidence; Antibody; Antigen; Blood; Chromosome; Circumstantial evidence; Crime scene investigation; Cross contamination; DNA; Epidemiology; Fluids; Hemoglobin; Homogeneous enzyme immunoassay (EMIT); Illicit drugs; Immune system; Luminol; Parasitology; Paternity evidence; Saliva; Serum; Toxicological analysis.