Disparate Intracellular Processing of Human IL-12 Preprotein Subunits: Atypical Processing of the P35 Signal Peptide

Type I IFNs, IFN-α and IFN-β, are early effectors of innate immune responses against microbes that can also regulate subsequent adaptive immunity by promoting antimicrobial Th1-type responses. In contrast, the ability of IFN-β to inhibit autoimmune Th1 responses is thought to account for some of the beneficial effects of IFN-β therapy in the treatment of relapsing remitting multiple sclerosis. To understand the basis of the paradoxical effects of IFN-β on the expression of Th1-type immune responses, we developed an in vitro model of monocyte-derived dendritic cell (DC)-dependent, human naive Th cell differentiation, in which one can observe both positive and negative effects of IFN-β on the generation of Th1 cells. In this model we found that the timing of IFN-β exposure determines whether IFN-β will have a positive or a negative effect on naive Th cell differentiation into Th1 cells. Specifically, the presence of IFN-β during TNF-α-induced DC maturation strongly augments the capacity of DC to promote the generation of IFN-γ-secreting Th1 cells. In contrast, exposure to IFN-β during mature DC-mediated primary stimulation of naive Th cells has the opposite effect, in that it inhibits Th1 cell polarization and promotes the generation of an IL-10-secreting T cell subset. Studies with blocking mAbs and recombinant cytokines indicate that the mechanism by which IFN-β mediates these contrasting effects on Th1 cell generation is at least in part by differentially regulating DC expression of IL-12 family cytokines (IL-12 and/or IL-23, and IL-27) and IL-18.

Section: Discussionmentioning

confidence: 99%

Timing of IFN-β Exposure during Human Dendritic Cell Maturation and Naive Th Cell Stimulation Has Contrasting Effects on Th1 Subset Generation: A Role for IFN-β-Mediated Regulation of IL-12 Family Cytokines and IL-18 in Naive Th Cell Differentiation

Nagai

Devergne

Mueller

et al. 2003

“…The human p35 promoter contains several putative transcription factor-binding elements including PU.1, CCAAT/enhancer binding protein, and GAS (IFN-␥ activation sequence). The p35 gene appears to initiate transcription from multiple sites (21,22), and there is evidence to suggest that the p35 gene may also be regulated at the level of post-translational processing (23,24).…”

Section: Suppression Of Il-12 Transcription In Macrophages Followingmentioning

confidence: 99%

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

Cappiello

Sutterwala

Trinchieri

et al. 2001

Ligating FcγR on macrophages results in suppression of IL-12 production. We show that FcγR ligation selectively down-regulates IL-12 p40 and p35 gene expression at the level of transcription. The region responsive to this inhibition maps to the Ets site of the p40 promoter. PU.1, IFN consensus sequence binding protein, and c-Rel form a complex on this element upon macrophage activation. Receptor ligation abolishes the binding of this PU.1-containing activation complex, and abrogates p40 transcription. A dominant-negative construct of PU.1 diminishes IL-12 p40 promoter activity and endogenous IL-12 p40 protein secretion. Thus, the specificity of IL-12 down-regulation following receptor ligation lies in the inhibition of binding of a PU.1-containing complex to the Ets site of the IL-12 promoter. These findings provide evidence demonstrating for the first time the importance of PU.1 in the transcriptional regulation of IL-12 gene expression.

“…The p40 subunit is strongly induced in APCs by bacterial and viral Ags, whereas the p35 subunit is constitutively transcribed (7,8). Within the endoplasmic reticulum, both subunits are joined together to form the bioactive IL-12p75 molecule (9). IL-12p75 has previously been shown to be the key factor for the induction of a Th1 immune response, which is essential to control infections with intracellular pathogens (10 -12).…”

mentioning

confidence: 99%

IL-12p40-Dependent Agonistic Effects on the Development of Protective Innate and Adaptive Immunity AgainstSalmonellaEnteritidis

Lehmann

Bellmann

Werner

et al. 2001

113

106

To study a potential IL-12p40-dependent but IL-12p75-independent agonistic activity regulating the immune response against Salmonella Enteritidis, the course of infection in IL-12p35-deficient mice (IL-12p35−/−, capable of producing IL-12p40) was compared with that of IL-12p40−/− mice. Mice lacking IL-12p40 revealed a higher mortality rate and higher bacterial organ burden than mice capable of producing IL-12p40. This phenotype was found in both genetically susceptible (BALB/c, Itys) and resistant mice (129Sv/Ev, Ityr) indicating Ity-independent mechanisms. The more effective control of bacteria in the IL-12p35−/− mice was associated with elevated serum IFN-γ and TNF-α levels. In contrast, IL-12p40−/− mice showed reduced IFN-γ production, which was associated with significantly elevated serum IgE levels. Early during infection (days 3 and 4 postinfection), as well as late (day 20 postinfection), the number of infected phagocytes was strongly increased in the absence of IL-12p40 indicating impaired bactericidal activity when IL-12p40 was missing. Liver histopathology revealed a decreased number of mononuclear granulomas in IL-12p40−/− mice. Depletion of CD4+ or CD8+ T lymphocytes in vivo suggested that both T cell subpopulations contribute to the IL-12p40-dependent protective functions. Analysis of IL-12p40 vs IL-23p19 mRNA expression revealed an up-regulation of only IL-12p40 mRNA during Salmonella infection. Together these data indicate that IL-12p40 can induce protective mechanisms during both the innate and the adaptive type 1 immune response in Salmonella infection. This novel activity of IL-12p40 complements the well described dominant and essential role of IL-12p75 in protective immunity to Salmonella infection.