Endotoxins of Gram-negative microbes fulfill as components of the outer membrane a vital function for bacterial viability and, if set free, induce in mammalians potent pathophysiological effects. Chemically, they are lipopolysaccharides (LPS) consisting of an O-specific chain, a core oligosaccharide, and a lipid component, termed lipid A. The latter determines the endotoxic activities and, together with the core constituent Kdo, essential functions for bacteria. The primary structure of lipid A of various bacterial origin has been elucidated and lipid A of Escherichia coli has been chemically synthesized. The biological analysis of synthetic lipid A partial structures proved that the expression of endotoxic activity depends on a unique primary structure and a peculiar endotoxic conformation. The biological lipid A effects are mediated by macrophage-derived bioactive peptides such as tumor necrosis factor alpha (TNF). Macrophages possess LPS receptors, and the lipid A regions involved in specific binding and cell activation have been characterized. Synthetic lipid A partial structures compete the specific binding of LPS or lipid A and antagonistically inhibit the production of LPS-induced TNF. LPS toxicity, in general, and the ability of LPS to induce TNF are also suppressed by a recently developed monoclonal antibody (IgG2a), which is directed against an epitope located in the core oligosaccharide. At present we determine molecular and submolecular details of the specificity of the interaction of lipid A with responsive host cells with the ultimate aim to provide pharmacological or immunological therapeutics that reduce or abolish the fatal inflammatory consequences of endotoxicosis.

AU-rich elements (AREs) in the 3' untranslated region (UTR) of unstable mRNAs dictate their degradation. An RNAi-based screen performed in Drosophila S2 cells has revealed that Dicer1, Argonaute1 (Ago1) and Ago2, components involved in microRNA (miRNA) processing and function, are required for the rapid decay of mRNA containing AREs of tumor necrosis factor-alpha. The requirement for Dicer in the instability of ARE-containing mRNA (ARE-RNA) was confirmed in HeLa cells. We further observed that miR16, a human miRNA containing an UAAAUAUU sequence that is complementary to the ARE sequence, is required for ARE-RNA turnover. The role of miR16 in ARE-RNA decay is sequence-specific and requires the ARE binding protein tristetraprolin (TTP). TTP does not directly bind to miR16 but interacts through association with Ago/eiF2C family members to complex with miR16 and assists in the targeting of ARE. miRNA targeting of ARE, therefore, appears to be an essential step in ARE-mediated mRNA degradation.

Interleukin-17A (IL-17A) is elaborated by the T helper 17 (T H 17) subset of T H cells and exhibits potent proinflammatory properties in animal models of autoimmunity, including collagen-induced arthritis, experimental autoimmune encephalomyelitis, and experimental autoimmune uveitis. To determine whether IL-17A mediates human inflammatory diseases, we investigated the efficacy and safety of AIN457, a human antibody to IL-17A, in patients with psoriasis, rheumatoid arthritis, and chronic noninfectious uveitis. Patients with chronic plaque-type psoriasis (n = 36), rheumatoid arthritis (n = 52), or chronic noninfectious uveitis (n = 16) were enrolled in clinical trials to evaluate the effects of neutralizing IL-17A by AIN457 at doses of 3 to 10 mg/kg, given intravenously. We evaluated efficacy by measuring the psoriasis area and severity index (PASI), the American College of Rheumatology 20% response (ACR20) for rheumatoid arthritis, or the number of responders for uveitis, as defined by either vision improvement or reduction in ocular inflammation or corticosteroid dose. AIN457 treatment induced clinically relevant responses of variable magnitude in patients suffering from each of these diverse immune-mediated diseases. Variable response rates may be due to heterogeneity in small patient populations, differential pathogenic roles of IL-17A in these diseases, and the different involvement or activation of IL-17A-producing cells. The rates of adverse events, including infections, were similar in the AIN457 and placebo groups. These results support a role for IL-17A in the pathophysiology of diverse inflammatory diseases including psoriasis, rheumatoid arthritis, and noninfectious uveitis.

Phosphorylation of mitogen-activated protein kinases (MAPKs) on specific tyrosine and threonine sites by MAP kinase kinases (MAPKKs) is thought to be the sole activation mechanism. Here, we report an unexpected activation mechanism for p38alpha MAPK that does not involve the prototypic kinase cascade. Rather it depends on interaction of p38alpha with TAB1 [transforming growth factor-beta-activated protein kinase 1 (TAK1)-binding protein 1] leading to autophosphorylation and activation of p38alpha. We detected formation of a TRAF6-TAB1-p38alpha complex and showed stimulus-specific TAB1-dependent and TAB1-independent p38alpha activation. These findings suggest that alternative activation pathways contribute to the biological responses of p38alpha to various stimuli.

We have cloned and characterized a new member of the p38 group of mitogen-activated protein kinases here termed p38␦. Sequence comparisons revealed that p38␦ is approximately 60% identical to the other three p38 isoforms but only 40 -45% to the other mitogen-activated protein kinase family members. It contains the TGY dual phosphorylation site present in all p38 group members and is activated by a group of extracellular stimuli including cytokines and environmental stresses that also activate the other three known p38 isoforms. However, unlike the other p38 isoforms, the kinase activity of p38␦ is not blocked by the pyridinyl imidazole, 4-(4-fluorophenyl)-2-2(4-hydroxyphenyl)-5-(4-pyridyl)-imidazole (identicalto SB202190). p38␦ can be activated by MKK3 and MKK6, known activators of the other isoforms. Nonetheless, in-gel kinase assays provide evidence for additional activators. The data presented herein show that p38␦ has many properties that are similar to those of other p38 group members. Nonetheless important differences exist among the four members of the p38 group of enzymes, and thus each may have highly specific, individual contributions to biologic events involving activation of the p38 pathways.