Antigen-Antibody Reaction
Definition
The specific non-covalent binding between an antigen (a molecule capable of eliciting an immune response) and the antibody produced against it. In forensic testing, this reaction is harnessed to detect target molecules in a specimen. Specificity of the reaction determines which fluid or species is identified.
- Bond type
- Non-covalent binding
- Field
- Forensic immunology and serology
- Key property
- Specificity determines target identification
- Typical use
- Species and body fluid identification
Common questions
What makes the antigen-antibody reaction useful in casework rather than just biology?+
Because the binding is highly specific to a matching antigen, a test built on this reaction can distinguish human blood from animal blood, or identify a particular body fluid, from a stain that gives no such information under a microscope alone.
Can this reaction give a false result?+
Cross-reactivity is the main limitation: an antibody raised against one antigen can sometimes bind a structurally similar antigen from another species or fluid, so confirmatory testing is used alongside a positive screening result rather than relying on one reaction alone.
How does this reaction differ from a DNA-based identification method?+
The antigen-antibody reaction detects a protein or other molecule present in a fluid or tissue, telling an examiner what the stain is, while DNA profiling targets genetic markers to tell an examiner whose cells are present, a separate question answered by a separate technique.
Related terms
- Anti-Human Serum
- Antibodies raised in a rabbit (or goat) by repeated injection of human serum. The rabbit's immune system makes IgG against human serum...
- Chain of Custody
- The documented chronological record of who collected, handled, transferred, and examined a piece of evidence. For digital evidence, chain of custody includes...
- COI Barcoding
- DNA-based species identification using a standard 658 bp segment of the mitochondrial cytochrome oxidase subunit I gene. Sequences are matched against reference...
- Cyt-B PCR
- Amplification and sequencing of the mitochondrial cytochrome-b gene. The reference marker for species identification in degraded and trace samples.
- ELISA (Enzyme-Linked Immunosorbent Assay)
- A plate-based immunoassay format in which a target antigen is captured by an antibody bound to a solid surface, detected by a...
- Immunoelectrophoresis
- A two-step technique: proteins are first separated by electrophoresis in agar gel, then antiserum diffuses from a parallel trough and forms precipitin...
- Lateral-Flow Immunoassay
- A point-of-care competitive immunochromatographic format on a nitrocellulose strip. In the absence of drug, colloidal gold-labelled antibody is captured at a test...
- Ouchterlony Double Diffusion
- A gel diffusion technique in which antigen and antibody placed in separate wells in an agar gel diffuse passively toward each other....
- Precipitin Reaction
- The formation of an insoluble antigen-antibody complex (precipitate) when soluble antigen and antibody meet at equivalent concentrations. The Ouchterlony double-diffusion test and...
- Precipitin Test
- A serological method in which an antiserum specific to one species' proteins is mixed with an extract of an unknown specimen. Formation...
- Species Identification (Forensic)
- The determination of whether biological material originates from a human or from a specific non-human species, using species-specific antisera (precipitin test) or...
- Uhlenhuth Test (1901)
- The original precipitin ring test devised by Paul Uhlenhuth in Greifswald. Layering anti-human serum under a dilute bloodstain extract gives a white...
Explained in these topics
- Determination of Species of Origin from Blood and Body FluidsSpecific non-covalent binding between an epitope on a protein antigen and the paratope on its matching antibody. Precipitin tests rely on this specificity at t...
- Scope of Forensic Immunology: Specimens and Contexts