Demonstration that nonspecific bovine Brucella abortus agglutinin is EDTA-labile and not calcium-dependent.

The binding site of B. abortus involved in nonspecific or false-positive agglutination by bovine serum was shown to be Ca++-independent in that binding of Ca++ by the chelating reagent DP2TA did not decrease titers. The reduction in agglutination by EDTA, EGTA, and DPTA was thought to be related to a common structural characteristic of these chelating reagents not exhibited by EDDA and DP2TA or to a lesser extent by DTPA. Removal of antigenic entities from the cell by the chelator was excluded as the cause of agglutination inhibition because agglutination by nonspecific IgM was not influenced by repeated washing of B. abortus by EDTA. The action of the chelators on the cell-agglutinin interaction was hypothesized to be a result of their competition with a receptor site on the cell for binding of the nonspecific or biochemically altered bovine IgM.