Serology

Forensic Serology Introduction

  • Forensic Serology: The study and identification of bodily materials as a preliminary step before DNA analysis.

    • Bodily Fluids of Interest:

      • Blood: Most commonly encountered in forensic investigations.

      • Semen

      • Vaginal fluid

      • Saliva

      • Sweat

      • Fecal matter

Importance of Identifying Bodily Fluids

  • Purpose: To ultimately facilitate DNA extraction and individualization of samples.

    • Other substances can also contain DNA, complicating identification.

    • Identifying bodily fluids can be challenging due to factors such as:

      • Color changes

      • Substrate color variations

    • Accurate identification aids in determining the origin of DNA evidence.

Blood Overview

  • Nature of Blood:

    • A highly complex mixture containing:

      • Cells

      • Enzymes

      • Proteins

      • Inorganic substances

    • Blood consists of suspended solid materials in plasma, accounting for 45% of blood content.

    • Plasma: The fluid portion of blood, composed mainly of water, comprising 55% of blood content.

Serum vs Plasma

  • Blood Clotting Mechanism:

    • Fibrin: A protein that traps and enmeshes red blood cells during blood clotting.

    • Centrifugation:

      • Clotted blood: Results in serum when centrifuged after clotting.

      • Anti-coagulated blood: Results in plasma when centrifuged with an anti-coagulant.

Red Blood Cells (RBCs)

  • Functions:

    • Transport oxygen from lungs to body tissues.

    • Remove CO2 from tissues by returning it to lungs for exhalation.

  • Forensically Important Features:

    • Antigens: Usually proteins and carbohydrates found on the surface of RBCs; crucial for determining blood type.

      • Antigens can stimulate antibody production.

Blood Typing History

  • 1901: Karl Landsteiner discovered blood typing and was awarded the Nobel Prize in 1930 for this finding.

    • Initial attempts at blood transfusion often led to coagulation and death due to incompatible blood types.

Blood Typing Systems

  • Classification:

    • Over 15 blood antigen systems identified.

    • Most important: A-B-O and Rh factor.

      • Blood Type Determination:

        • Presence of A and B antigens defines blood type:

          • Type A: Has A antigens.

          • Type B: Has B antigens.

          • Type AB: Has both A and B antigens.

          • Type O: Has neither A nor B antigens.

    • Rh Factor (D antigen): Also impacts blood typing.

      • If D antigen is present: Rh positive (+).

      • If D antigen is absent: Rh negative (-).

Antibody Functionality

  • Antibodies:

    • Y-shaped proteins found in plasma/serum.

    • Function: Neutralize pathogens by tagging antigens, enabling the immune system to attack.

    • Properties:

      • Usually bivalent, allowing them to form a network through cross-links.

      • Lead to agglutination (clumping) in blood typing tests.

Blood Typing Methods

  • Serology: The study of blood and immune system reactions, specifically focusing on antigens and serum antibody interactions.

    • Blood Typing Tests:

      • Test blood samples for the presence of A, B, and D antigens by adding anti-A and anti-B serum and checking for agglutination.

    • Antiserum Reactions:

      • Anti-A Serum + Whole Blood provides indication of A type presence.

      • Anti-B Serum + Whole Blood gives feedback on B type presence.

Population Blood Type Statistics

  • Blood type distributions in the population:

    • Type O: 43% - lacks A or B antigens, has both anti-A and anti-B antibodies.

    • Type A: 42% - has A antigens, only anti-B antibodies.

    • Type B: 12% - has B antigens, only anti-A antibodies.

    • Type AB: 3% - has both A and B antigens, lacks both antibodies.

Forensic Considerations in Blood Testing

  • Preliminary Testing: Determining whether a substance is blood is best achieved through preliminary color tests.

    • Based on hemoglobin's peroxidase-like activity.

    • Test kits like TMB, KM, and LMG demonstrate color change when hemoglobin is present.

Specific Blood Color Tests

  • Types of Tests:

    • TMB Test: Utilizes tetramethylbenzidine, turns blue/green when positive.

    • Kastle-Meyer (KM) Test: Uses phenolphthalein, gives a pink result when positive.

    • LMG Test: Applies leucomalachite green that turns blue/green when positive.

  • Trace Detection: Luminol and Bluestar tests for tracing blood stains:

    • Luminol: Sensitive to diluted blood; produces luminescence under dark conditions.

    • Bluestar: Similar to Luminol but visible without complete darkness.

Confirmatory Blood Tests

  • Confirmatory Tests Needed: Following screening tests, confirmatory tests like microcrystalline tests (Takayama and Teichmann) must be utilized to confirm presence.

    • Takayama Test: Forms rhomboid hemochromogen crystals.

    • Teichmann Test: Produces brown haemin crystals.

  • Current Methods: Immunochromatography techniques used to confirm human versus animal blood. RSID detects human Glycophorin A, ABAcard HemaTrace identifies human hemoglobin.

Blood Origin Testing

  • Precipitin Test: Tests the reaction of human antigens with specific animal antibodies derived from injected human blood to rabbits.

  • Sensitivity: Extremely sensitive method; can react to ancient dried blood or even low amounts.

  • Gel Diffusion Test: Antigens and antibodies diffuse toward each other in a gel medium; precipitation results indicate a reaction.

Individualizing Bloodstains

  • Historically, A-B-O typing was used to associate blood with individuals, but DNA analysis has revolutionized identification methods, making ABO typing largely redundant in modern forensics.

Immunoassay Techniques in Forensics

  • General Principles: Utilizing antigen-antibody interactions to develop immunoassays for detecting the presence of substances like drugs in blood and urine.

    • Antibodies produced against drugs introduced into animals through a protein-carrier combination.

  • Types of Immunoassays:

    • Competitive vs. Non-competitive: Differ in use of labeled drugs.

      • Homogeneous vs. Heterogeneous: Distinguish based on the need for washing between steps.

Genetic Basis of Blood Type

  • Inheritance: Blood types controlled by specific antigen alleles and are genetically inherited from parents, making them useful in forensic investigations.

  • Genes and Chromosomes: Basic units of heredity; humans have approximately 30,000 recognized genes organized on 46 chromosomes, contributing to traits, including blood type characteristics.

    • Genotypes (AA, AO) determine phenotypes (blood types A, B, AB, O).

    • Understanding genotype versus phenotype is crucial for interpretations in forensic contexts.

Semen in Forensic Contexts

  • Male Reproductive Fluid: Comprises seminal fluid and sperm, significance heightened in forensic analysis for sexual offenses.

    • Detection Process: Two steps - locating the stain and confirming that it is semen.

Seminal Stain Testing

  • Visibility: Seminal stains may be readily visible, but can be missed if they are small or background-cleaned. Utilize alternate light sources for detection.

  • Presumptive Test: Based on acid phosphatase (AP) activity; purple color indicates the presence.

  • Confirmatory Test for Sperm: Microscopic analysis required, identifying sperm morphology.

  • Other Unique Compounds: PSA and semenogelin indicators used for confirmation via immunological tests.

Sexual Assault Evidence Collection

  • Importance of preserving semen evidence to imply sexual activity; absence of semen does not negate the occurrence of sexual assault.

  • Carefully collect and package evidence from victims and suspects to prevent contamination and loss.

Timing and Persistence of Semen Evidence

  • The persistence of seminal constituents in victims can establish timelines post-interaction, considering various timeframes for sperm motility and protein presence.

Biological Evidence Packaging

  • Best Practices:

    • Avoid airtight containers to prevent moisture accumulation that could degrade DNA.

    • Each stained item must be packaged separately in breathable materials to ensure integrity before lab analysis.

Other Bodily Fluids

  • Saliva Testing: Utilizes specific tests for detection based on enzymes present; RSID saliva tests for human-specific indications.

  • Urine Testing: Various chemical tests and immunoassays identify unique compounds in urine samples.

  • Sweat Detection: The least common fluid found at crime scenes, analyzed through certain chemical compositions.

  • Vaginal Fluid: Requires established testing methods to identify components indicating a sexual context, as well as potential false positives.

  • Fecal Matter: Not technically a bodily fluid but tested via urobilinogen detection and microscopic examination for verification.