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Interferons (IFNs) were discovered nearly 60 years ago as a family of cytokines induced during and protecting from viral infection. They have been documented to play essential roles in numerous physiological processes beyond innate antiviral defense, including immunomodulation, regulation of the cell cycle, cell survival and differentiation, and the host response to microbial pathogens. Recent data have also uncovered a potentially darker side to the functions of IFN, including roles in autoimmunity and diabetes. Many IFN effects occur in the absence of acute viral infection, highlighting a physiologic role for constitutively produced IFN. Type I IFNs are constitutively produced at vanishingly low quantities and yet exert profound effects, mediated at least in part through modulation of signaling intermediates required for diverse cytokine response pathways. We review evidence for a yin-yang of IFN function through its role in modulating crosstalk between multiple cytokines by both feed-forward and feed-back regulation of common signaling intermediates and postulate that a similar mechanism underlies a homeostatic role for IFN through tonic signaling in the absence of acute infection.

SUMMARY Mitochondria are functionally and physically associated with heterotypic membranes, yet little is known about how these interactions impact mitochondrial outer-membrane permeabilization (MOMP) and apoptosis. We observed that dissociation of heterotypic membranes from mitochondria inhibited BAK/BAX-dependent cytochrome c (cyto c) release. Biochemical purification of neutral sphingomyelinases that correlated with MOMP sensitization suggested that sphingolipid metabolism coordinates BAK/BAX activation. Using purified lipids and enzymes, sensitivity to MOMP was achieved by in vitro reconstitution of the sphingolipid metabolic pathway. Sphingolipid metabolism inhibitors blocked MOMP from heavy membrane preparations but failed to influence MOMP in the presence of sphingolipid-reconstituted, purified mitochondria. Furthermore, the sphingolipid products, sphingosine-1-PO4 and hexadecenal, cooperated specifically with BAK and BAX, respectively. Sphingolipid metabolism was also required for cellular responses to apoptosis. Our studies suggest that BAK/BAX activation and apoptosis are coordinated through BH3-only proteins and a specific lipid milieu that is maintained by heterotypic membrane-mitochondrial interactions

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Tumor necrosis factor (TNF) ␣ has been shown to be a major therapeutic target in rheumatoid arthritis with the success of anti-TNF␣ antibody clinical trials. Although signaling pathways leading to TNF␣ expression have been studied in some detail, there is evidence for considerable differences between individual cell types. This prompted us to investigate the intracellular signaling pathways that result in increased TNF␣ synthesis from macrophages in the diseased synovial joint tissue. Using an adenoviral system in vitro we report the successful delivery of genes to more than 95% of normal human macrophages. This permitted us to show, by using adenoviral transfer of IB␣, the natural inhibitor of NF-B, that induction of TNF␣ in normal human macrophages by lipopolysaccharide, but not by some other stimuli, was inhibited by 80%. Furthermore the spontaneous production of TNF␣ from human rheumatoid joint cell cultures was inhibited by 75%, indicating that the NF-B pathway is an essential step for TNF␣ synthesis in synovial macrophages and demonstrating that NF-B should be an effective therapeutic target in this disease.