TNFα-stimulated gene-6 (TSG6), a 30-kDa protein generated by activated macrophages, modulates inflammation; however, its mechanism of action and role in the activation of macrophages are not fully understood. Here we observed markedly augmented LPS-induced inflammatory lung injury and mortality in TSG6^−/− mice compared with WT (TSG6^+/+) mice. Treatment of mice with intratracheal instillation of TSG6 prevented LPS-induced lung injury and neutrophil sequestration, and increased survival in mice. We found that TSG6 inhibited the association of TLR4 with MyD88, thereby suppressing NF-κB activation. TSG6 also prevented the expression of proinflammatory proteins (iNOS, IL-6, TNFα, IL-1β, and CXCL1) while increasing the expression of anti-inflammatory proteins (CD206, Chi3l3, IL-4, and IL-10) in macrophages. This shift was associated with suppressed activation of proinflammatory transcription factors STAT1 and STAT3. In addition, we observed that LPS itself up-regulated the expression of TSG6 in TSG6^+/+ mice, suggesting an autocrine role for TSG6 in transitioning macrophages. Thus, TSG6 functions by converting macrophages from a proinflammatory to an anti-inflammatory phenotype secondary to suppression of TLR4/NF-κB signaling and STAT1 and STAT3 activation.

Rationale:: TRPM2 (transient receptor potential melastatin-2) expressed in endothelial cells (ECs) is a cation channel mediating Ca ²⁺ entry in response to intracellular generation of adenosine diphosphoribose—the TRPM2 ligand. Objective:: Because polymorphonuclear neutrophils (PMN) interaction with ECs generates reactive oxygen species, we addressed the possible role of TRPM2 expressed in ECs in the mechanism of transendothelial migration of PMNs. Methods and Results:: We observed defective PMN transmigration in response to lipopolysaccharide challenge in adult mice in which the EC expressed TRPM2 is conditionally deleted ( Trpm2 ^iΔEC ). PMN interaction with ECs induced the entry of Ca ²⁺ in ECs via the EC-expressed TRPM2. Prevention of generation of adenosine diphosphoribose in ECs significantly reduced Ca ²⁺ entry in response to PMN activation of TRPM2 in ECs. PMNs isolated from gp91phox ^−/− mice significantly reduced Ca ²⁺ entry in ECs via TRPM2 as compared with wild-type PMNs and failed to induce PMN transmigration. Overexpression of the adenosine diphosphoribose insensitive TRPM2 mutant channel (C1008→A) in ECs suppressed the Ca ²⁺ entry response. Further, the forced expression of TRPM2 mutant channel (C1008→A) or silencing of poly ADP-ribose polymerase in ECs of mice prevented PMN transmigration. Conclusions:: Thus, endotoxin-induced transmigration of PMNs was secondary to TRPM2-activated Ca ²⁺ signaling and VE-cadherin phosphorylation resulting in the disassembly of adherens junctions and opening of the paracellular pathways. These results suggest blocking TRPM2 activation in ECs is a potentially important means of therapeutically modifying PMN-mediated vascular inflammation.

The transcriptional repressor DREAM is involved in pain sensing. Tiruppathi and colleagues show that it is also involved in innate signaling by regulating the anti-inflammatory deubiquitinase A20. Here we found that the transcription repressor DREAM bound to the promoter of the gene encoding A20 to repress expression of this deubiquitinase that suppresses inflammatory NF-κB signaling. DREAM-deficient mice displayed persistent and unchecked A20 expression in response to endotoxin. DREAM functioned by transcriptionally repressing A20 through binding to downstream regulatory elements (DREs). In contrast, binding of the transcription factor USF1 to the DRE-associated E-box domain in the gene encoding A20 activated its expression in response to inflammatory stimuli. Our studies define the critical opposing functions of DREAM and USF1 in inhibiting and inducing A20 expression, respectively, and thereby the strength of NF-κB signaling. Targeting of DREAM to induce USF1-mediated A20 expression is therefore a potential anti-inflammatory strategy for the treatment of diseases associated with unconstrained NF-κB activity, such as acute lung injury.

Stromal interacting molecule 1 (STIM1) regulates store-operated Ca²⁺ entry (SOCE). Here we show that STIM1 expression in endothelial cells (ECs) is increased during sepsis and, therefore, contributes to hyperpermeability. LPS induced STIM1 mRNA and protein expression in human and mouse lung ECs. The induced STIM1 expression was associated with augmented SOCE as well as a permeability increase in both in vitro and in vivo models. Because activation of both the NF-κB and p38 MAPK signaling pathways downstream of TLR4 amplifies vascular inflammation, we studied the influence of these two pathways on LPS-induced STIM1 expression. Inhibition of either NF-κB or p38 MAPK activation by pharmacological agents prevented LPS-induced STIM1 expression. Silencing of the NF-κB proteins (p65/RelA or p50/NF-κB1) or the p38 MAPK isoform p38α prevented LPS-induced STIM1 expression and increased SOCE in ECs. In support of these findings, we found NF-κB and AP1 binding sites in the 5′-regulatory region of human and mouse STIM1 genes. Further, we demonstrated that LPS induced time-dependent binding of the transcription factors NF-κB (p65/RelA) and AP1 (c-Fos/c-Jun) to the STIM1 promoter. Interestingly, silencing of c-Fos, but not c-Jun, markedly reduced LPS-induced STIM1 expression in ECs. We also observed that silencing of p38α prevented c-Fos expression in response to LPS in ECs, suggesting that p38α signaling mediates the expression of c-Fos. These results support the proposal that cooperative signaling of both NF-κB and AP1 (via p38α) amplifies STIM1 expression in ECs and, thereby, contributes to the lung vascular hyperpermeability response during sepsis.

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.