Evaluation of lymphocyte blastogenesis for diagnosis of bovine brucellosis.

The lymphocyte blastogenesis test (LBT) was evaluated for its usefulness in the diagnosis of bovine brucellosis. Using a cell titration assay which measures the blastogenic response over a range of cell concentrations, peripheral blood lymphocytes (PBL) from various populations of cattle were tested with purified Brucella abortus porin proteins and with Brucella abortus soluble antigen (BASA). Cattle tested included groups infected with virulent B. abortus strain 2308, vaccinated with B. abortus strain 19, infected with Escherichia coli strain 0116:H31 (known to cause serological cross reactions with B., abortus), vaccinated with a bacterin of Staphylococcus aureus, and unimmunized controls. Pregnant heifers vaccinated with strain 19 could generally be distinguished from pregnant animals infected with virulent strain 2308 when LBT responses to porin were analyzed by comparing maximum delta counts per minute (the responses of the cell concentration at which there is the greatest difference between stimulation in the presence of antigen and without antigen). However, a group of nonpregnant heifers infected with strain 2308 either failed to react or reacted in an inconsistent fashion with porin or BASA. The lack of responsiveness in the LBT was accompanied by high concentrations of circulating agglutinins. False positive responses also occurred to porin, although much less frequently than to the crude preparation BASA. The use of nylon wool fractionated PBL did not provide an improved means for distinguishing Brucella infected from uninfected cattle. Based on these findings, we would not recommend the LBT with either of these antigens as a routine method for diagnosis. Lipopolysaccharide was extracted from B. abortus strain 2308 and tested for its role in inducing false positive responses. Although there exist components in B. abortus extracts which are mitogenic for bovine PBL, our data do not support such a function for purified Brucella LPS.