Anti-globulin tests - Coombes Test

Mechanism: In order to detect "incomplete" antibody (i.e. antibody with only one attachment site) this test adds a step in which chicken anti-globulin is used to "bridge the gap" between complexes of antigen coated with the incomplete antibody and hence induce agglutination.

Reagents: The reagents are the same as for the standard agglutination test with the addition of the chicken anti-globulin. This is a solution of antibodies prepared by immunizing another species (usually goat or rabbit) by injecting it with purified chicken globulins.

Methods: Usually this involves the addition of one step to the "slow agglutination in micro-titre plate" test.

Assays: To date this has only be used for non-host-specific avian Salmonellae (Williams and Whittemore, 1976). Species of Salmonellae which are not very tissue-invasive induce a rather poor and variable agglutinin response.

Comments: This test has never been widely used in the UK and has had only limited application in the U.S. However the same principle (using an anti-globulin to identify the presence of an antibody) has become widely used in a number of other tests (indirect immunofluorescence, and Elisa tests, see below).