CD40 ligation prevents Trypanosoma cruzi infection through interleukin-12 upregulation

Because of the critical role of the CD40-CD40 ligand (CD40L) pathway in the induction and effector phases of immune responses, we investigated the eff ects of CD40 ligation on the control of Trypanosoma cruzi infection. First, we observed that supernatants of murine spleen cells stimulated by CD40L-t ransfected 3T3 fibroblasts (3T3-CD40L transfectants) prevent the infection of mouse peritoneal macrophages (MPM) by T. cruzi. This phenomenon depends on de novo production of nitric oxide (NO) as it is prevented by the additi on of N-nitro-L-arginine methyl ester, a NO synthase inhibitor. NO producti on requires interleukin (IL)-12-mediated gamma interferon (IFN-gamma) and t umor necrosis factor alpha (TNF-alpha) synthesis as demonstrated by inhibit ion experiments using neutralizing anti-IL-12 anti-IFN-gamma, and anti-TNF- alpha monoclonal antibodies (MAb), We found that an activating anti-CD40 MA b also directly stimulates IFN-gamma-activated MPM to produce NO and thereb y to control T, cruzi infection. To determine the in vivo relevance of thes e in vitro findings, mice were injected with 3T3-CD40L transfectants or 3T3 control fibroblasts at the time of T. cruzi inoculation. We observed that in vivo CD40 ligation dramatically reduced both parasitemia and the mortali ty rate of T. cruzi-infected mice. A reduced parasitemia was still observed when the injection of 3T3-CD40L transfectants was delayed 8 days postinfec tion. It was abolished by injection of anti-IL-12 MAb. Taken together, thes e data establish that CD40 ligation facilitates the control of T. cruzi inf ection through a cascade involving IL-12, IFN-gamma, and NO.