Definition

Noun 1. A specific type of antibody: A precipitin is an antibody that reacts with its corresponding soluble antigen to form a visible, insoluble complex that settles out of solution (precipitates).

Usage

• The precipitin reaction is a classic immunological test used to identify antigens.
• Scientists used a precipitin test to confirm the presence of the bacterial toxin in the serum sample.
• The formation of a cloudy line where the antigen and precipitin meet is a positive result.

Advanced Usage

• Precipitin line/band: The visible line of precipitate formed in immunodiffusion or immunoelectrophoresis techniques where specific antigen and antibody (precipitin) meet at optimal proportions.
  • The Ouchterlony double immunodiffusion assay showed a sharp precipitin line, indicating identity between the two antigens.
• Precipitin reaction: The specific immunochemical reaction leading to the formation of an insoluble antigen-antibody complex.
  • The precipitin reaction is dependent on the bivalent nature of antibodies and the multivalency of antigens.

Variants and Related Words

• Precipitate (verb): To cause a substance to be deposited in solid form from a solution. This is the action performed by the precipitin.
• Precipitation (noun): The process of forming a precipitate; also used specifically for the precipitin reaction.
• Immunoprecipitation (noun): A broader laboratory technique that uses antibodies to precipitate a specific antigen out of solution for further analysis.

Synonyms

• Precipitating antibody: A direct descriptive synonym.
• Agglutinin is a related but distinct term for an antibody that causes clumping (agglutination) of or antigens, rather than precipitation of soluble ones.

Notes on Meaning

The term "precipitin" is highly specific to the field of immunology and serology. Its core, defining function is to cause the precipitation of a soluble antigen. It is not a general term for any antibody.

Noun

1. an antibody that causes precipitation when it unites with its antigen