Conditions for conducting the indirect hemolysis test for detection of antibodies to Brucella abortus.

Some conditions were examined for performing the indirect hemolysis test for bovine brucellosis. An antigen extracted by using dimethyl sulfoxide was used for all of the assays. Optimal results were obtained by using bovine erythrocytes coated with alkali-treated antigen at a concentration of 800 micrograms/ml. Exceeding this level did not give greater sensitivity. The sensitivity of the test could be decreased by increasing the number of coated erythrocytes used in the test. Evidence was also provided for the presence of heat-labile antibodies in the sera of vaccinated cattle. Heat treatment (58 degrees C for 50 min) caused a reduction in titer of all sera tested. It was also shown that lysis of erythrocytes was complete in less than 60 min. Therefore, it would be possible to reduce the time needed for analysis. Non-alkali-treated ("native") antigen would bind to bovine erythrocytes, but it was less effective in the test than alkali-treated material. Erythrocytes coated with relatively large amounts of the native antigen were less suspectible to lysis than were cells which had been treated with lower concentrations.