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Since LPS was discovered, all inquiry in the field was motivated by two articles of faith. First, it was held that LPS was an important factor in microbial pathogenesis. Second, it was held that the responses elicited by numerous molecules of microbial origin might be formally similar to the responses elicited by LPS. The identification of TLR4 as the core transducer of LPS responses, and the added discovery that other TLR paralogs sense other microbial products, has strongly validated these cherished beliefs. M oreover, it has amalgamated many separate lines of inquiry, and focused attention on the how the innate immune system perceives infection.

Since the first description of dendritic cells by Steinman and Cohn in 1973, this important cell type has gained increasing attention. Over 4000 papers have been published on this topic annually during the last few years. At the beginning, dendritic cells were recognized for their immune stimulatory properties and their importance in initiating an adaptive immune response. Later, it was found that dendritic cells do not only initiate but also regulate immune responses. This attribute makes the so-called regulatory dendritic cells highly important for the prevention of exaggerated immune responses. Immune cells make contact with different Ags every day and must be tightly controlled to prevent excessive inflammation and subsequent organ destruction, particularly in organs such as the gut and lungs. Here, we give a brief overview of our current knowledge on how immune responses are controlled by dendritic cells, highlighting how they are involved in the induction of peripheral tolerance. We focus on what is known about these processes in the lung, with a closer look at their role in the induction and control of diseases such as bronchial asthma, chronic obstructive pulmonary disease and lung infections. Finally, we summarize some current approaches to modulate the behavior of dendritic cells that may hopefully lead to future therapeutics to control exaggerated immune responses.

Lipopolysaccharides (LPSs) from Gram-negative bacteria are strong elicitors of the human immune systems. There is strong evidence that aggregates and not monomers of LPS play a decisive role at least in the initial stages of cell activation of immune cells such as mononuclear cells. In previous reports, it was shown that the biologically most active part of enterobacterial LPS, hexa-acyl bisphosphorylated lipid A, adopts a particular supramolecular conformation, a cubic aggregate structure. However, little is known about the size and morphology of these aggregates, regarding the fact that LPS may have strong variations in the length of the saccharide chains (various rough mutant and smooth-form LPS). Thus, in the present paper, several techniques for the determination of details of the aggregate morphology such as freeze-fracture and cryo-electron microscopy, analytical ultracentrifugation, laser backscattering analysis, and small-angle X-ray scattering were applied for various endotoxin (lipid A and different LPS) preparations. The data show a variety of different morphologies not only for different endotoxins but also when comparing different applied techniques. The data are interpreted with respect to the suitability of the single techniques, in particular on the basis of available literature data.

Mammalian systems respond to environmental stress by either adapting for survival or undergoing programmed cell death (apoptosis). While it is generally believed that the caspase family of proteases are essential effectors of the apoptotic response, much less is clear about the signaling machinery required to activate the caspase system in response to stress stimuli. In the past few years, increasing evidence has linked the sphingomyelin and c-jun kinase (JNK) pathways to the death response in various cellular systems. Both signaling pathways are evolutionarily conserved through yeast. Since yeast does not undergo apoptosis, these pathways appear evolutionarily older than the caspase-mediated death programs. This paper reviews the role of sphingomyelin/ceramide and the JNK pathways in co-ordinating the signaling events leading to apoptosis.

Mucosal surfaces represent a natural colonization site for Gram-negative bacteria. We have already demonstrated the biologic role of Salmonella typhimuriumporins in vitro and in vivo. In this paper we studied mucosal and systemic interleukin-6 (IL-6) and tumor necrosis factor α (TNFα) production in systematically challenged mice or after intravesical administration of LPS or porins from S. typhimurium.It was found that serum IL-6 levels increased in BALB/c mice 4 h after receiving either i.v. LPS or porins from S. typhimurium.The porin challenge was stronger. Serum IL-6 levels were higher after porins than after LPS. IL-6 was not detected in the urine of i.v. challenged mice. Findings regarding IL-6 urine levels in intravesically treated mice were comparable. In porin-challenged mice they decreased more slowly than the LPS-challenged ones. IL-6 was not detected in the serum of intravesically challenged mice. In i.v. LPS-challenged mice, serum TNFα levels peaked earlier (at 2 h) than the IL-6 levels. A higher 2 h peak was instead seen in porin-challenged mice. TNFα was not detected in the urine of i.v. challenged mice. With intravesical LPS challenge, urinary TNFα levels peaked at 24 h, whereas in the porin-challenged mice the peak occurred 12 h earlier and was higher. Serum samples revealed no detectable TNFα. These findings confirm that both porins and LPS activate the mucosal response, without any systemic involvement, as, for example, in patients with diseases such as pyelonephritis or gastroenteritis.

The development of effective pharmacotherapies to combat the Adult Respiratory Distress Syndrome (ARDS) is critically dependent upon: (1) the development of clinically-relevant animal models; (2) identification of inflammatory mediators centrally involved in eliciting lung injury; (3) understanding the inter-relationships or 'cross-talk' between pro and anti-inflammatory mediators which modulate the lung inflammation; and (4) the application of molecular techniques to isolate potentially novel genes involved in the development of ARDS. In this paper, we will present evidence from a rat model of microvascular lung injury produced by interleukin-2 (IL-2), that pulmonary TNFα is a primary and pivotal mediator of lung injury and that different modes of TNFα inhibition may represent feasible strategies to prevent ARDS. Furthermore, we will describe how the application of Differential Display Reverse Transcriptase Polymerase Chain Reaction (DDRT-PCR) can allow the rapid isolation of partial fragments of potentially new genes involved in ARDS. The products of such genes could represent future target sites for pharmacotherapeutic intervention.

Endotoxin is thought to play a major role in septic shock and multiple systemic organ failure (MOF). However, endotoxin is not always detected in the plasma during Gram-negative sepsis by current Limuluslysate assays. Additionally, it is unknown to what extent the biological activity of endotoxin is truly reflected in endotoxemia. This paper assesses quantitatively a comparison of three types of Limulusassays for the detection of the biological activity of endotoxin in plasma. Mouse lethal activity and TNF production were used for assessment of the biological activity of endotoxin both before and after potential modification of LPS activity by plasma constituents. We have concluded that the dilution and heating method coupled with a toxinometer provides the most accurate correlation with other biological activities of endotoxin in plasma. The fact that the biological activity of endotoxin decreased to 17% of initial dose after incubation at 37ºC for 90 min in normal plasma suggests further a temporal dependence of time in plasma upon the manifestation of biological activities normally attributable to this biologically active microbial constituent found in the plasma of septic patients.

It is now well recognized that plasma LPS-binding protein (LBP) and membrane CD14 present at the surface of cells of the myelo/monocytic lineage are central molecules of the innate immune system, in response to LPS or to bacterial products. This paper reviews the role of LBP and CD14 in models of endotoxemia and infection.