Spur Formation
Definition
In Ouchterlony, a spur is formed when one arc curves beyond another due to an excess of a cross-reacting but non-identical antigen. It indicates partial cross-reactivity rather than species identity.
- Test
- Ouchterlony double diffusion
- Cause
- Cross-reacting, non-identical antigen
- Interpretation
- Partial cross-reactivity, not identity
- Contrast
- A true line of identity shows no spur
Common questions
How does a spur pattern differ from a line of identity on an Ouchterlony plate?+
A true line of identity forms a smooth, unbroken arc between adjacent wells, while a spur shows one arc curving past and continuing beyond the other, signalling that the antisera recognise an antigen the two samples do not fully share.
Can spur formation lead to a false species identification if misread?+
Yes, an examiner who mistakes a spur for a full identity line could wrongly conclude two samples are the same species, which is why interpretation guidelines require checking for arc continuity rather than presence of a reaction alone.
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 Arc / Line
- The visible band of precipitate in an Ouchterlony plate where diffusing antigen and diffusing antibody meet. Its shape and relationship to adjacent...
- 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...