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Infect. Immun., Jul 1996, 2782-2786, Vol 64, No. 7
Y Zhan, Z Liu and C Cheers
Both interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-alpha) are
produced early in intracellular bacterial infection. Depletion of either
IL-12 or TNF-alpha by a single injection of specific antibody 4 h before
the injection of Brucella abortus 19 led to the exacerbation of infection 2
weeks later. Whereas the effect of IL-12 depletion on resistance was
persistent and exacerbation was still significant 6 weeks later, the
bacterial numbers in mice depleted of TNF-alpha were similar to the
bacterial numbers in control infected mice by 6 weeks postinfection.
Massive splenomegaly, which is often seen in 2-week Brucella-infected mice,
was not observed in IL-12- or TNF-alpha- depleted mice. Both IL-12- and
TNF-alpha-depleted mice showed reduced cell accumulation in the spleen
compared with the massive cell accumulation in control infected mice.
Granuloma formation in livers was much reduced in IL-12-depleted mice but
not in TNF-alpha-depleted mice. Gamma interferon (IFN-gamma) production by
cells from TNF-alpha- depleted mice was not significantly different from
that of cells from control infected mice. In contrast, the production of
IFN-gamma by both CD4+ and CD8+ T cells from IL-12-depleted mice was
greatly reduced, compared with that from control infected mice. This effect
was still observed when the antibody injection was delayed for up to 7 days
postinfection, but injections of anti-IL-12 antibody into mice with
established Brucella infection had no significant effect on IFN-gamma
production by T cells. Taken together, these results suggested that IL- 12
contributed to resistance mainly via an IFN-gamma-dependent pathway and had
a profound effect on the induction of acquired cellular resistance. In
contrast, TNF-alpha was involved in resistance possibly via direct action
on effector cells and may not be essential for the induction of acquired
cellular resistance.
Copyright © 1996, American Society for Microbiology
Tumor necrosis factor alpha and interleukin-12 contribute to resistance to the intracellular bacterium Brucella abortus by different mechanisms
Department of Microbiology, University of Melbourne, Parkville, Victoria, Australia.
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