Precipitin Arc / Line
Definition
The visible band of precipitate in an Ouchterlony plate where diffusing antigen and diffusing antibody meet. Its shape and relationship to adjacent arcs encodes species identity.
- Test format
- Ouchterlony double diffusion
- Formation
- Where diffusing antigen meets diffusing antibody
- Encodes
- Species identity via shape and adjacency
- Appearance
- Visible band of precipitate
Common questions
How does the relationship between adjacent arcs reveal species identity?+
When two antigen wells are tested against the same antiserum, arcs that fuse smoothly into one continuous line indicate identical antigens, arcs that cross indicate unrelated antigens, and a partial spur pattern indicates partial cross-reactivity, letting an analyst infer species relationships from geometry alone.
What limits the sensitivity of the Ouchterlony precipitin line method?+
Diffusion-based precipitin testing requires relatively fresh, reasonably concentrated protein and is far less sensitive than modern DNA-based species testing, so it has largely been superseded by molecular methods for degraded or trace forensic samples while remaining useful for well-preserved stains.
Related terms
- Antiserum (Pl. Antisera)
- Blood serum from an animal (typically a rabbit) that has been immunised against the proteins of another species. It contains antibodies that...
- Double Immunodiffusion (Ouchterlony)
- A gel diffusion method in which both antigen and antibody diffuse toward each other from separate wells in agar. Precipitin bands form...
- Precipitin Test
- A serological method in which an antiserum specific to one species' proteins is mixed with an extract of an unknown specimen. Formation...
- Ring Precipitin Test
- A tube-based precipitin assay in which the antiserum is carefully underloaded beneath the sample; a ring of precipitate at the interface indicates...
- Spur Formation
- In Ouchterlony, a spur is formed when one arc curves beyond another due to an excess of a cross-reacting but non-identical antigen....