Induction of Specific Cytotoxic Lymphocytes in Mice Vaccinated with Brucella abortus RB51

A safe, more sensitive, nonradioactive, neutral red uptake assay was adopted to replace the traditional (51)Cr release assay for detection of Brucella-specific cytotoxic T lymphocyte (CTL) activity. Our studies indicated that Brucella abortus strain RB51 vaccination of mice induced specific CTLs against both strain RB51- and strain 2308-infected J774.A1 macrophages but not against Listeria monocytogenes-infected J774.A1 cells. The antigen-specific cytotoxic activity was exerted by T lymphocytes but not by NK cells. CD3(+) CD4(+) T cells secreted the highest level of gamma interferon (IFN-γ) and were able to exert a low but significant level of specific lysis of Brucella-infected macrophages. They also exerted a low level of nonspecific lysis of noninfected macrophages. In contrast, CD3(+) CD8(+) T cells secreted low levels of IFN-γ but demonstrated high levels of specific lysis of Brucella-infected macrophages with no nonspecific lysis. These findings indicate that B. abortus strain RB51 vaccination of mice induces specific CTLs and suggest that CD3(+) CD4(+) and CD3(+) CD8(+) T cells play a synergistic role in the anti-Brucella activity.