A novel cell-based system for the rapid quantitative evaluation of (anti)-inflammatory potential of test substances.

The control of NF-kappaB activation is a proven therapeutic strategy in the treatment of multiple inflammatory disorders. Drug discovery and development for such a therapy demands a battery of assays to reliably demonstrate both clinical effectiveness and biological safety of prospective medications. Unlike traditional in vitro biochemical analyses, cell-based assays more closely mimic the actual in vivo physiologic environment, addressing simultaneously biological activity and toxicity issues. A novel assay system, based solely on the drug resistance of a genetically engineered cell line, has been developed to provide rapid quantitative evaluation of the (anti)-inflammatory potential of test substances. The assay principle is based on the ability of bona fide inflammatory agents to activate the transcription factor NF-kappaB in cultured cells. In our model, expression of a dual drug resistance marker, driven by an NF-kappaB-dependent minimal promoter, provides a selective and highly sensitive scheme with a quantitative readout to detect biochemical agents with pro-or anti-inflammatory properties. The novel cell-based system is inexpensive, simple to perform (requiring only basic cell culture skills), accurate, and provides sensitivity comparable to that of the electrophoretic mobility shift assay and quantitative ELISA. In addition, the dual selection capability of the model provides a powerful tool to discover novel molecular components of the NF-kappaB signal transduction pathway.

Induction of in vitro reprogramming by Toll-like receptor (TLR)2 and TLR4 agonists in murine macrophages: effects of TLR "homotolerance" versus "heterotolerance" on NF-kappa B signaling pathway components.

In this study, tolerance induction by preexposure of murine macrophages to Toll-like receptor (TLR)2 and TLR4 agonists was revisited, focusing on the major signaling components associated with NF-kappaB activation. Pretreatment of macrophages with a pure TLR4 agonist (protein-free Escherichia coli (Ec) LPS) or with TLR2 agonists (Porphyromonas gingivalis LPS or synthetic lipoprotein Pam3Cys) led to suppression of TNF-alpha secretion, IL-1R-associated kinase-1, and IkappaB kinase (IKK) kinase activities, c-jun N-terminal kinase, and extracellular signal-regulated kinase phosphorylation, and to suppression of NF-kappaB DNA binding and transactivation upon challenge with the same agonist (TLR4 or TLR2 "homotolerance," respectively). Despite inhibited NF-kappaB DNA binding, increased levels of nuclear NF-kappaB were detected in agonist-pretreated macrophages. For all the intermediate signaling elements, heterotolerance was weaker than TLR4 or TLR2 homotolerance with the exception of IKK kinase activity. IKK kinase activity was unperturbed in heterotolerance. TNF-alpha secretion was also suppressed in P. gingivalis LPS-pretreated, Ec LPS-challenged cells, but not vice versa, while Pam3Cys and Ec LPS did not induce a state of cross-tolerance at the level of TNF-alpha. Experiments designed to elucidate novel mechanisms of NF-kappaB inhibition in tolerized cells revealed the potential contribution of IkappaBepsilon and IkappaBxi inhibitory proteins and the necessity of TLR4 engagement for induction of tolerance to Toll receptor-IL-1R domain-containing adapter protein/MyD88-adapter-like-dependent gene expression. Collectively, these data demonstrate that induction of homotolerance affects a broader spectrum of signaling components than in heterotolerance, with selective modulation of specific elements within the NF-kappaB signaling pathway.

Cyclosporin A blocks the expression of lymphotoxin alpha, but not lymphotoxin beta, in human peripheral blood mononuclear cells.

The 2 lymphotoxin subunits LTalpha (also called tumor necrosis factor beta [TNF-beta]) and LTbeta belong to the family of TNF-related cytokines. They form either a soluble homotrimeric ligand (LTalpha(3)) that binds to and signals through CD120a/b (TNFRp55 and TNFRp75), or a membrane-associated heterotrimeric ligand (LTalpha(1)beta(2)) that binds to and signals through the LTbeta receptor (LTbetaR). In mice, LTbetaR signaling is critical for the maintenance of peripheral lymphoid tissues and optimal immune responses, and its down-regulation results in immunodeficiency. To determine the possible relationship between LT-mediated immunodeficiency and the immunosuppressive effects of cyclosporin A (CsA), we tested the effects of CsA on the expression of LTalpha and LTbeta in human peripheral blood mononuclear cells (PBMCs). When PBMCs were stimulated with phorbol myristate acetate/ionomycin or with anti-CD3/anti-CD28, the accumulation of LTalpha both at mRNA and protein levels was markedly inhibited by CsA. This inhibition is likely due to CsA's effect on the nuclear factor of activated T cell (NFAT) proteins binding to a novel NFAT-binding element at position -490 relative to LTalpha transcription start. LTbeta showed a distinct expression pattern and was insensitive to CsA. Thus, in addition to its effects on the expression of other TNF family members, such as TNFalpha, CD40-L, and CD95-L, CsA can block expression of surface LT complex by selectively inhibiting the expression of the LTalpha subunit. We propose that LT dysfunction and its downstream effects may contribute to immunosuppressive effects of CsA.

Adenovirus type 5 vectors induce dendritic cell differentiation in human CD14(+) monocytes cultured under serum-free conditions.

To determine whether infection by a model virus is capable of initiating dendritic cell (DC) differentiation, human CD14(+) peripheral blood monocytes were infected with replication-defective type 5 adenovirus. Under serum-free conditions, this resulted in differentiation of a majority of cells toward a DC phenotype within 36 to 48 hours, without the need for cytokine-induced predifferentiation. Infection induced DC morphology and altered the expression of surface markers, including loss of CD14, de novo induction of CD83 and CD25, and strongly augmented expression of CD86, CD80, CD40, and HLA-DR and HLA class I molecules. Differentiated cells maintained immunophenotype without loss of viability for at least 2 days after removal of the differentiation agent and cytokines. A greatly enhanced capacity to stimulate T-lymphocyte alloproliferation and increased expression of the DC-associated transcription factor RelB were observed. Virus without transgene was found to induce changes similar to transgene-expressing viruses. RelB up-regulation and DC immunophenotype were sensitive to the antioxidant N-acetylcysteine, suggesting a critical role for nuclear factor kappaB. RNAse protection assays revealed elevated levels of messenger RNA for a number of chemokines and cytokines associated with DCs. Finally, during differentiation, adenovirus-infected monocytes were shown to secrete chemokines and cytokines, including tumor necrosis factor-alpha (TNF-alpha). Furthermore, a TNF-alpha-neutralizing antibody inhibited the expression of some DC surface markers, indicating a contributing role for this cytokine in the adenovirus-induced differentiation of DC from monocytes. These findings have implications for the biology of monocytes as precursors to DCs and also for the use of recombinant adenovirus in vaccines or gene therapy.