Interferon Consensus Sequence Binding Protein–deficient Mice Display Impaired Resistance to Intracellular Infection Due to a Primary Defect in Interleukin 12 p40 Induction

Abstract

Mice lacking the transcription factor interferon consensus sequence binding protein (ICSBP), a member of the interferon regulatory factor family of transcription proteins, were infected with the intracellular protozoan, Toxoplasma gondii. ICSBP-deficient mice exhibited unchecked parasite replication in vivo and rapidly succumbed within 14 d after inoculation with an avirulent Toxoplasma strain. In contrast, few intracellular parasites were observed in wild-type littermates and these animals survived for at least 60 d after infection. Analysis of cytokine synthesis in vitro and in vivo revealed a major deficiency in the expression of both interferon (IFN)-γ and interleukin (IL)-12 p40 in the T. gondii exposed ICSBP−/− animals. In related experiments, macrophages from uninfected ICSBP−/− mice were shown to display a selective impairment in the mRNA expression of IL-12 p40 but not IL-1α, IL-1β, IL-1Ra, IL-6, IL-10, or TNF-α in response to live parasites, parasite antigen, lipopolysaccharide, or Staphylococcus aureus. This selective defect in IL-12 p40 production was observed regardless of whether the macrophages had been primed with IFN-γ. We hypothesize that the impaired synthesis of IL-12 p40 in ICSBP−/− animals is the primary lesion responsible for the loss in resistance to T. gondii because IFN-γ–induced parasite killing was unimpaired in vitro and, more importantly, administration of exogenous IL-12 in vivo significantly prolonged survival of the infected mice. Together these findings implicate ICSBP as a major transcription factor which directly or indirectly regulates IL-12 p40 gene activation and, as a consequence, IFN-γ–dependent host resistance.

Suppression of IL-12 Transcription in Macrophages Following Fcγ Receptor Ligation

“…IL-12 drives type I immune responses, primarily by virtue of its ability to induce the production of IFN-␥ from T and NK cells. A number of studies have shown that animals deficient in IL-12 are more susceptible to infections by intracellular organisms (1,2), and conversely that the addition of exogenous IL-12 can promote protective immune responses to these organisms (3,4). Despite its conspicuous role in driving cellular immune responses, the overproduction of IL-12 can be detrimental to the host.…”

An IFN-γ-Inducible Transcription Factor, IFN Consensus Sequence Binding Protein (ICSBP), Stimulates IL-12 p40 Expression in Macrophages

“…Samples were purified by phenol-chloroform and resolved in 6% PAGE. Details of RNase protection assays were described (24).…”

“…Further, ICSBP Ϫ/Ϫ mice express a very low level of constitutive IL-12 p40 transcripts and are unable to induce the transcripts in response to infections (23,24). Accordingly, ICSBP Ϫ/Ϫ mice are highly susceptible to infection by Listeria monocytogenes, Toxoplasma gondii, Leishmania major, and lymphocytic choriomeningitis virus and vaccinia viruses (23)(24)(25)(26). The study performed with the Toxoplasma model attributed this susceptibility to a specific defect in macrophages to induce IL-12 p40 mRNA (24).…”

“…Furthermore, ICSBP negatively regulates transcription of IFN-responsive genes through the IFN-stimulated response element (ISRE) sequence (22). Further, ICSBP Ϫ/Ϫ mice express a very low level of constitutive IL-12 p40 transcripts and are unable to induce the transcripts in response to infections (23,24). Accordingly, ICSBP Ϫ/Ϫ mice are highly susceptible to infection by Listeria monocytogenes, Toxoplasma gondii, Leishmania major, and lymphocytic choriomeningitis virus and vaccinia viruses (23)(24)(25)(26).…”

“…Accordingly, ICSBP Ϫ/Ϫ mice are highly susceptible to infection by Listeria monocytogenes, Toxoplasma gondii, Leishmania major, and lymphocytic choriomeningitis virus and vaccinia viruses (23)(24)(25)(26). The study performed with the Toxoplasma model attributed this susceptibility to a specific defect in macrophages to induce IL-12 p40 mRNA (24). Recently, Wu et al showed that ICSBP Ϫ/Ϫ APCs are unresponsive to the stimulation by CD40/ CD40 ligand interactions, indicating that T cell-dependent induction of IL-12 p40 also requires ICSBP (27), consistent with an earlier work (26).…”