Ouchterlony

Ouchterlony refers to the double immunodiffusion technique developed by the Swedish immunologist Sven Ouchterlony. Also known as the Ouchterlony assay or double diffusion, it is a classical method used to study antigen–antibody reactions in a solid gel, typically agarose, by allowing both components to diffuse toward each other.

In the procedure, wells are formed in a gel plate: wells contain different antigens and an antibody solution. The antigens and antibody diffuse from their wells into the surrounding gel, and precipitin lines form where the diffuse antigen and antibody meet at equivalence. After incubation, the pattern of lines is observed and interpreted.

Interpretation focuses on relationships among antigens. Identity is indicated when precipitin lines from two antigens meet the antibody line and fuse into a single, continuous arc with no spur. Partial identity shows a spur, suggesting shared epitopes but not complete identity between antigens. Non-identity is indicated by intersecting or crossed lines, implying distinct antigens recognized by different epitopes.

Applications have included characterizing antigenic relationships among microbial or fungal antigens, verifying antigen identity, and assessing antibody specificity in serology. The method provided foundational insights into antigenic structure and relatedness before the advent of more sensitive techniques.

Limitations include its semi-quantitative nature, subjective interpretation of line patterns, and relatively low sensitivity. Modern diagnostics more commonly employ ELISA, Western blot, or other immunoassays, but the Ouchterlony technique remains a historic and educational tool and is still used in some teaching laboratories and specialized investigations.