Stability of freeze dried horseradish peroxidase conjugated monoclonal antibodies used in diagnostic serology.

Two murine monoclonal antibodies, an IgG1 isotype specific for the heavy chain of bovine IgG1, the second an IgG3 isotype and specific for an epitope of the O-polysaccharide of Brucella abortus were conjugated with horseradish peroxidase. The conjugated antibodies were freeze dried in the presence of a number of additives to preserve activity and tested for stability over an 18 month period. Addition of 0.3M trehalose or 0.8% lactalbumin and 3.2% sucrose resulted in the lowest loss of activity if the conjugated antibodies were freeze dried in glass vials. Freeze drying in polypropylene vials resulted in a more rapid rate of deterioration with some additives or an accelerated rate of decline after an initial plateau of lesser loss of activity. The use of polypropylene vials and lactalbumin and sucrose were included in this study because of their low cost compared to glass vials and trehalose. While each antibody behaved differently, addition of trehalose or lactalbumin and sucrose to the conjugated antibodies aided in the preservation of enzyme activity. Both additives provide a suitable method for long term storage of freeze dried or freeze dried and reconstituted monoclonal antibody-enzyme conjugates.