INTERLEUKIN-12 (IL-12) AND IL-18 SYNERGISTICALLY INDUCE THE FUNGICIDAL ACTIVITY OF MURINE PERITONEAL-EXUDATE CELLS AGAINST CRYPTOCOCCUS-NEOFORMANS THROUGH PRODUCTION OF GAMMA-INTERFERON BY NATURAL-KILLER-CELLS

We examined the ability of interleukin-12 (IL-12) and IL-18 to induce the production of gamma interferon (IFN-gamma) and nitric oxide (NO) b y murine peritoneal exudate cells (PEG) and to stimulate the growth in hibitory activity of these cells against Cryptococcus neoformans. PEC produced IFN-gamma and NO when stimulated with a combination of IL-12 and IL-18 but little or no IFN-gamma or NO when either cytokine was us ed alone, PEC anticryptococcal activity was mediated by IFN-gamma and NO production, since it was completely inhibited by a neutralizing ant i-IFN-gamma monoclonal antibody (MAb) and N-G-monomethyl-L-arginine, a competitive inhibitor of NO synthesis, respectively, To identify the IFN-gamma-producing cells among PEC stimulated with IL-12 and IL-18, r ye depleted NK cells, gamma delta T cells, or CD4(+) T cells by treati ng PEC with specific Abs and complement, NK cell depletion strongly su ppressed IFN-gamma production and almost completely inhibited NO produ ction and anticryptococcal activity, while depletion of other cells ha d no such influence. Alternatively, purified NK cells by two cycles of glass adherence and magnetic separation with anti-CD3, -CD4, -CD8, an d -B220 MAbs produced a greater amount of IFN-gamma by stimulation wit h IL-12 and IL-18 than unseparated non-glass-adherent PEG. Our results demonstrated that IL-12 and IL-18 synergistically induced NO-dependen t anticryptococcal activity of PEC by stimulating NK cells to produce IFN-gamma.