IL-12 and Type-I IFN Synergize for IFN-γ Production by CD4 T Cells, Whereas Neither Are Required for IFN-γ Production by CD8 T Cells afterListeria monocytogenesInfection

Abstract

Differentiation of Ag-specific T cells into IFN-γ producers is essential for protective immunity to intracellular pathogens. In addition to stimulation through the TCR and costimulatory molecules, IFN-γ production is thought to require other inflammatory cytokines. Two such inflammatory cytokines are IL-12 and type I IFN (IFN-I); both can play a role in priming naive T cells to produce IFN-γ in vitro. However, their role in priming Ag-specific T cells for IFN-γ production during experimental infection in vivo is less clear. In this study, we examine the requirements for IL-12 and IFN-I, either individually or in combination, for priming Ag-specific T cell IFN-γ production after Listeria monocytogenes (Lm) infection. Surprisingly, neither individual nor combined defects in IL-12 or IFN-I signaling altered IFN-γ production by Ag-specific CD8 T cells after Lm infection. In contrast, individual defects in either IL-12 or IFN-I signaling conferred partial (∼50%) reductions, whereas combined deficiency in both IL-12 and IFN-I signaling conferred more dramatic (75–95%) reductions in IFN-γ production by Ag-specific CD4 T cells. The additive effects of IL-12 and IFN-I signaling on IFN-γ production by CD4 T cells were further demonstrated by adoptive transfer of transgenic IFN-IR+/+ and IFN-IR−/− CD4 T cells into normal and IL-12-deficient mice, and infection with rLm. These results demonstrate an important dichotomy between the signals required for priming IFN-γ production by CD4 and CD8 T cells in response to bacterial infection.

Deviation from a Strong Th1-Dominated to a Modest Th17-Dominated CD4 T Cell Response in the Absence of IL-12p40 and Type I IFNs Sustains Protective CD8 T Cells

“…However, combined defects in both IL-12p40 and type I IFN signaling completely abrogate IFN-␥ production and Th1 differentiation by Ag-specific CD4 T cells (17). For the optimal study of the adaptive T cell response using mice with targeted defects in immune response pathways known to play either protective or detrimental roles in innate susceptibility to WT Lm infection, we used infection with attenuated Lm strains with targeted deficiency in actA to prime adaptive T cell immunity and normalize Ag load after infection.…”

“…1 day before Lm infection. For in vitro culture, splenocytes were plated into 96-well round-bottom plates (5 ϫ 10 6 cells/ml) and stimulated with the indicated peptides (10 Ϫ6 M) for 5 h (intracellular cytokine staining) or 72 h (culture supernatants) as described elsewhere (17). For intracellular cytokine staining, brefeldin A (BD GolgiPlug reagent) was added to cell cultures before peptide stimulation.…”

“…The recombinant Lm strain, Lm-OVA, and Lm-OVA ⌬actA derived from this strain through targeted deletion in the actA gene have been described previously (17,18). For infections, Lm were grown to early log phase (OD 600 , 0.1) in brain-heart infusion medium (BD Biosciences) at 37°C, washed, and diluted with saline to a 200-l final volume and injected i.v.…”

“…For Lm infection, Ag-specific CD8 T cells confer the majority of the protective effects, whereas CD4 T cells have an important role in the generation of long-lived memory CD8 T cells (14 -16). Using this infection model, we have recently demonstrated that priming Ag-specific CD4 T cells for IFN-␥ production requires either IL-12 or type I IFNs, while priming Ag-specific CD8 T cells requires neither IL-12 nor type I IFNs (17). Furthermore, for CD4 T cells activated in the absence of IL-12 and type I IFNs, the lack of IFN-␥ production is not associated with a reciprocal production of Th2 cytokines such as IL-4 or IL-13 (17).…”

“…Using this infection model, we have recently demonstrated that priming Ag-specific CD4 T cells for IFN-␥ production requires either IL-12 or type I IFNs, while priming Ag-specific CD8 T cells requires neither IL-12 nor type I IFNs (17). Furthermore, for CD4 T cells activated in the absence of IL-12 and type I IFNs, the lack of IFN-␥ production is not associated with a reciprocal production of Th2 cytokines such as IL-4 or IL-13 (17). Accordingly, in the present study, we examined the possibility that Lm infection in the absence of both IL-12p40 and IFN-IR signaling could prime a Th17-dominated response.…”