Cytokine response of T-cell subsets from Brucella abortus-infected mice to soluble Brucella proteins

Hot saline extracts of Brucella abortus 19 were separated by successive differential precipitation with 50 and 70% ammonium sulfate, yielding fractions SBP50, with predominantly 36-kDa proteins and a number of medium-sized proteins (26 to 33 kDa), and SBP70, with 14-kDa and lower-molecular-mass proteins. Both fractions stimulated specifically proliferation and cytokine production by spleen cells from brucella-infected mice, although the activity of SBP50 was much higher than that of SBP70. Further separation of SBP50 by a DEAE-Sepharose column resulted in three distinct subfractions which were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The three subfractions were analyzed for their abilities to induce lymphocytes to proliferate and produce cytokines. The three subfractions were all active but with characteristic differences in magnitude. Subfraction 1 stimulated moderate proliferation, high interleukin 6 (IL-6) production, and relatively low production of gamma interferon (IFN-gamma). Subfraction 2 was the strongest stimulus for proliferation and production of IL-6 and IFN-gamma, while subfraction 3 stimulated moderate cell proliferation, a high level of IFN-gamma, and a low level of IL-6. IL-2 production stimulated by the three subfractions was similar. SBP50 and all three subfractions stimulated purified T cells of both CD4+ and CD8+ subsets to produce IFN-gamma. The production of IFN-gamma by CD8+ T cells to brucella antigens was enhanced with exogenous IL-2.