Role of TNF-α in the induction of fungicidal activity of mouse peritoneal exudate cells against Cryptococcus neoformans by IL-12 and IL-18

We nave recently demonstrated that two IFN-γ-inducing cytokines, interleukin (IL)-12 and IL-18, synergistically induced the fungicidal activity of mouse peritoneal exudate cells (PEC) against Cryptococcus neoformans through NK cell production of interferon (IFN)-γ and nitric oxide (NO) synthesis. In the present study, we further dissected these effects by examining the involvement of tumor necrosis factor (TNF)-α in the induction of IL-12/IL-18-stimulated PEC fungicidal activity. The addition of neutralizing anti-TNF-α mAb significantly suppressed IL-12/IL-18-stimulated PEC anticryptococcal activity. This effect was ascribed to the inhibition of macrophage NO synthesis, but not of IFN-γ production by NK cells, because the same treatment inhibited the former response, but not the latter one. On the other hand, combined treatment with IL-12 and IL-18 synergistically induced the production of TNF-α by PEC and this effect was almost completely abrogated by neutralizing anti-IFN-γ mAb. The cell type producing TNF-α among PEC was mostly macrophage. TNF-α significantly promoted macrophage NO production and anticryptococcal activity induced by IFN-γ, and furthermore anti-TNF-α mAb partially inhibited these responses. Considered together, our results indicated that TNF-α contributed to the potentiation of IL-12/IL- 18-induced PEC fungicidal activity against C. neoformans through enhancement of IFN-γ-induced production of NO by macrophages, but not through increased production of IFN-γ by NK cells.