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Forensic Serology

Forensic Serology. Johnston Sr. High Forensics Mrs. Florio. Learning Objectives. 1) List the A-B-O antigens and antibodies found in the blood for each of the 4 different blood types – A, B, AB, O 2) Understand and describe how whole blood is typed

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Forensic Serology

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  1. Forensic Serology Johnston Sr. High Forensics Mrs. Florio

  2. Learning Objectives • 1) List the A-B-O antigens and antibodies found in the blood for each of the 4 different blood types – A, B, AB, O • 2) Understand and describe how whole blood is typed • 3) List and describe forensic tests used to characterize a stain as blood

  3. Learning Objectives (continued) • 4) Understand the concept of antigen/antibody interactions and how it is applied to species identification and drug identification • 5) Understand the inheritance of blood types

  4. History • Karl Landsteiner – figured out blood was categorized – won Noble Prize • All human blood is not the same • Blood transfusions were previously a failure before this time • Developed ABO system • How may blood help at a crime scene?

  5. The Nature of Blood • Mixture of cells, enzymes, proteins, and inorganic substances • Fluid portion – plasma • Mostly water, 55% of blood content • Suspended in plasma – cells (45%) • Red blood cells (erythrocytes) • White blood cells (leukocytes) • Platelets • Yellow portion in pic is serum (shown when Clotting factor in blood is removed, centrifuged)

  6. Antigens • Role of RBCs? • Transport oxygen to body tissues and remove carbon dioxide from tissues • On surface of all RBCs there are millions of chemical structures called ANTIGENS • a substance, usually a protein, that stimulates the body to produce antibodies against it

  7. How does this relate to blood type? • Blood Type A – each RBC has A antigens on surface • Blood Type B – RBCs have B antigens • Blood Type AB – RBCs have both A and B antigens • Blood Type O – RBCs don’t have either A or B antigen

  8. What about the Rh factor? + or -? • Rh factor – another antigen, sometimes called the D antigen • If you have it on RBCs = + • If you lack it = - • In blood banks, they must look for the presence of A, B, and Rh factor before donating blood

  9. Antibodies • Serum contains proteins called antibodies • Protein in the serum that destroys or inactivates a specific antigen • Anti-A – specific for only A antigen • Anti-B - for only B antigen • Anti-D – for only D antigen • Antiserum – blood serum containing specific antibodies

  10. Antigen-Antibody relationship • Antibody reacts only with its specific antigen • Serum with anti-B added to RBC carrying B antigen, two will combine, causing antibody to attach itself to cell • Antibodies are bivalent – have 2 reactive sites, can attach to 2 RBCs

  11. Agglutination • Antibody’s ability to be bivalent creates vast network of cross-linked cells seen as clumping, or agglutination. • Normal blood (L) antigens & antibodies coexist b/c antibodies present are not specific towards any of antigens • A foreign serum was added to blood (R) and causes antigen/antibody reaction, causing RBCs to link (agglutinate)

  12. Blood Groups

  13. Blood Typing • Serology – study of antigen-antibody reactions • Ex: ABO identity • Type A type is agglutinated by anti-A serum (not natural) • Type B aggl. by anti-B • Type AB aggl. by both anti-A and anti-B • Type O aggli. by neither antibody sera

  14. Population Distribution of Blood Type • O – 43% • A – 42% • B – 12% • AB – 3%

  15. Population Frequencies

  16. Cool Website on Blood Typing • http://nobelprize.org/educational_games/medicine/landsteiner/readmore.html • Blood Typing Game

  17. Level 6 Article Quiz • Name one example of a test to detect blood. • What are the four different blood types? • What are the three main antigens? Where are they found specifically? • What do antibodies do to antigens? • Name 3 components to blood.

  18. Level 6 continued… 6) What term describes the way blood flows slowly? a) water y b) viscosity c) spatter 7)Which blood type has the highest frequency? (most common, neglecting Rh) 8) A person with blood type B has ____ antigens and ___ antibodies.

  19. Level 6 continued… 9) Blood that flies off a surface under pressure is a(n) __________ stain. a) projected b) transfer c) colloid 10) WBCs make up ___ percent of total blood volume. a) 50% b) 10% c) 5% 11) This is the name for a test used to determine if blood is animal or human.

  20. Level 7 Quiz • Which scientist was responsible for organizing blood into types? • If you have blood type O, with blood types can you receive? • Name the 4 main blood types. • What are the three “solid” parts in the blood?

  21. Level 7 continued… 5) Be specific…where are antigens found? 6) Someone with blood type AB has ______ antigens and ____ antibodies. 7) What is the most common blood type? (neglecting Rh) 8) Term describing the ability of antibodies to attach to 2 antigen site.

  22. Forensic Characterization of Bloodstains • Questions the criminalist must ask regarding blood stains… • 1) Is it blood? • 2) From what species does the blood originate? • 3) If blood is human, how closely can it be associated with a particular individual?

  23. Types of Tests • Presumptive • Is It Blood, Semen, Urine, Saliva? • Look for proteins, substance activity • Confirmatory • Confirms the presence of the bodily fluid

  24. COLOR TESTS – Presumptive test for Blood • Kastle-Meyer Test • Based on the fact that blood hemoglobin possesses peroxidase-like activity • Hemoglobin: RBC protein that transports oxygen • Peroxidases: enzymes that accelerate the oxidation of many organic compound when combined with peroxides • Combination of blood, peroxide, & phenolthaleinreagant produces pink color

  25. More on Kastle-Meyer • Why is it not confirmatory? • False positives – oxidizing metals, potatoes, horseradish

  26. Luminol – Another Presumptive Test for Blood • Reaction of luminol with blood produces light, rather than color • Must darken room – will produce a faint, blue glow – luminescence • Extremely sensitive, capable of detecting bloodstains diluted up to 300,000 times

  27. Luminol – What you see

  28. Takayama – Confirmatory for blood • Tests for human hemoglobin • Small amount of blood added to microscope slide • Chemical solution is added and heated • Crystals viewed under microscope • Also uses microscopy to detect blood cells

  29. Precipitin Test • Human or animal origin? • Precipitin – antibody that reacts with its corresponding antigen to form a precipitate • when animals are injected with human blood, antibodies form that react with the invading human blood to neutralize its presence

  30. Gel Diffusion • Antibodies and antigens will diffuse or move toward one another on a plate made with a gel medium (agar). • Can also do this under influence of electrical field (electrophoresis)

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