Regulation of type 2 nitric oxide synthase by type 1 interferons in macrophages infected with Leishmania major

We recently reported that the infection of macrophages with Leishmania majo r led to the release of type 1 interferons (IFN-alpha/beta). Moreover, at d ay 1 of infection of mice with L. major, IFN-alpha/beta was required for th e expression of type 2 (inducible) NO synthase (NOS2 or iNOS) which, howeve r, was restricted to a few macrophages in the dermis. Here, we further char acterized the regulation of NOS2 by IFN-alpha/beta. Macrophages that were e ither simultaneously or sequentially exposed to L. major promastigotes and IFN-alpha/beta expressed NOS2 and antileishmanial activity, In contrast, wh en high amounts of IFN-alpha/beta were used or when IFN-alpha/beta was adde d to the macrophages 2 h prior to the parasites, almost no induction of NOS 2 was observed. After pretreatment with IFN-alpha/beta, tyrosine phosphoryl ation and nuclear DNA binding of Slat1 alpha, the degradation of the NF-kap pa B inhibitor (I kappa B alpha and beta), and the nuclear translocation of NF-kappa B were strongly impaired compared with macrophages exposed to IFN -alpha/beta and L. major simultaneously. Thus, IFN-alpha/beta exerts agonis tic or antagonistic effects on the expression of NOS2 in macrophages infect ed with a microbial pathogen, depending on the sequence of the stimuli and the amount of IFN-alpha/beta added. The limited number of NOS2-positive mac rophages at day 1 of infection in vivo might result from a blockage of noni nfected macrophages by IFN-alpha/beta that is released by neighboring infec ted cells.