Serology & Immunology

Innate Immune System

Non-Specificity: Provides a general defense against pathogens, recognizing broad patterns shared by many microbes

• Immediate Response: It acts quickly, providing an initial defense

• Components: It includes physical barriers (like skin), immune cells (such as macrophages and neutrophils), and proteins (like complement) that help eliminate pathogens

Adaptive Immune System

Specificity: The adaptive immune system targets specific pathogens using receptors that recognize unique antigens on the surface of microbes

• Memory: It generates immunological memory, allowing for faster and stronger responses upon subsequent exposures to the same pathogen.

• Components: It involves T cells (cell-mediated immunity) and B cells (humoral immunity), which produce antibodies to neutralize pathogens

Immunogens

• Any foreign substance can elicit an immune response

• Capable of combining with specific antibodies produced

• Not just viruses or bacteria - toxins and drugs too

Antigens

Any foreign substance that is capable of reacting with an antibody!

Hapten

Foreign substance of small molecular weight

• Cannot elicit antibody production on their own

• Generally, bound to protein carriers to become immunogenic

Antibody

Produced by lymphocytes in response to antigens

• Capable of binding specifically to antigens in order to neutralize them

• Made up of 1 or more copies of a “Y” shaped unit

  • 2 heavy chains

  • 2 light chain

Antibodies are specific and are made for specific antigens

Antibody - Antigen Binding

Specificity:

The ability of an antibody to react with only one antigen

Cross Reactivity:

The ability of an antibody to react with more than one antigen

Binding Strength

Affinity:

Strength of the interaction between antibody and antigen

Avidity:

• Strength of the overall antibody antigen complex

• Sum of all other binding affects

Antibody binding strength influences specificity and its ability to cross react with multiple antigens and form clusters

Reaction Types

Precipitation:

• Antigens are free floating

• Can form cross linking matrix

• Linking can be big enough to see with naked eye

• Antigens and antibodies bind, forming a lattice structure that precipitates out of solution, used to detect the presence of the antigen

Agglutination:

• Antigens are on cell surface

• Causes cells to clump

Blood Typing

3 genetic markers produce 4 possible blood types:

• A, B, AB, and O

Determined by immunological tests

Blood

Case Types:

• Homicide

• Aggravated Assault

Target Protein:

• Hemoglobin

• 4 tertiary subunits

• 2 alpha chains

• 2 beta chains

Seminal Fluid

Case Types:

• Rape

• Sexual Assault

Target Cell:

• Sperm

Target Protein:

• Semenogelin

  • Give semen its gel like matrix

• Prostate Specific Antigen

  • Enzyme that cleaves Semenogelin

Saliva

Case Types

• Homicide

• Aggravated Assault

• Rape/Sexual Assault

• Breaking and Entering

Target Protein:

• Alpha Amylase

  • Enzyme that cleaves starch molecules

Presumptive Tests

• Indicate the possible presence of a body fluid

• All serology tests but one

Confirmatory Tests

• Verifies the accuracy of the initial test result

• Direct detection

• Only one test available

Only Microscopy of sperm cells

Immunological Assays

• Used for all body fluid screening

• Commercially available

• Rely on antibody antigen binding events

• Precipitation

High Dose Hook Effect

• Extremely high concentrations of the target analyte in an immunoassay lead to a false negative result

• Excess analyte saturates the reagent binding sites, preventing proper formation of the detection complex → give a lower or undetectable signal, even though the analyte concentration is actually high. This effect can be avoided by diluting the sample

Colormetric Testing

• Tests for protein presence

• Uses molecule conjugation

• Hemastix

• Kastle-Meyer Leucomalachite Green

• Acid Phosphatase

Enzymatic Testing

• Testing for presence of enzyme

• Looking for enzymatic activity not just enzyme presence

• Phadebas Testing-Saliva

Spermatozoa

Head Region:

• Contains the nucleus

• Acrosome: enzymes important for fertilization

Midpiece:

• Mitochondria bank for energy

Tail Region:

• Motility