Differential induction of macrophage-derived cytokines by live and dead intracellular bacteria in vitro.

Marked differences in the abilities of living and heat-killed Brucella abortus and Listeria monocytogenes organisms to induce production of tumor necrosis factor alpha by in vitro-cultured macrophages were observed. Interleukin-1 and interleukin-6 appeared to be under different control. The results are discussed in relation to the induction of gamma interferon-producing Th1 cells and acquired cellular resistance to infection by living vaccines but not killed vaccines.