Mast cells are essential for early onset and severe disease in a murine model of multiple sclerosis.

In addition to their well characterized role in allergic inflammation, recent data confirm that mast cells play a more extensive role in a variety of immune responses. However, their contribution to autoimmune and neurologic disease processes has not been investigated. Experimental allergic encephalomyelitis (EAE) and its human disease counterpart, multiple sclerosis, are considered to be CD4(+) T cell-mediated autoimmune diseases affecting the central nervous system. Several lines of indirect evidence suggest that mast cells could also play a role in the pathogenesis of both the human and murine disease. Using a myelin oligodendrocyte glycoprotein (MOG)-induced model of acute EAE, we show that mast cell-deficient W/W(v) mice exhibit significantly reduced disease incidence, delayed disease onset, and decreased mean clinical scores when compared with their wild-type congenic littermates. No differences were observed in MOG-specific T and B cell responses between the two groups, indicating that a global T or B cell defect is not present in W/W(v) animals. Reconstitution of the mast cell population in W/W(v) mice restores induction of early and severe disease to wild-type levels, suggesting that mast cells are critical for the full manifestation of disease. These data provide a new mechanism for immune destruction in EAE and indicate that mast cells play a broader role in neurologic inflammation.

STAT6-independent production of IL-4 by mast cells.

The acquisition of an IL-4-producing phenotype in Th2 cells requires IL-4 signaling through the STAT6 pathway during T cell differentiation. In this study we demonstrate that, unlike in naive T cells, IL-4 is not necessary for the development of an IL-4-producing phenotype in mast cells. Bone marrow-derived mast cell precursors from STAT6-/- mice can differentiate into mature cells that express IL-4 levels comparable to those of wild-type mast cells. In differentiated mast cells, activation in the presence of neutralizing anti-IL-4 antibodies or mutation of the consensus STAT6 sites does not diminish IL-4 promoter activity, indicating that IL-4 is not required for active transcription. Taken together, these data suggest that mast cell IL-4 production is not STAT6 dependent, providing evidence that these cells could generate IL-4 needed for the initiation and amplification of an effective Th2 immune response.

IL-4 preferentially activates a novel STAT6 isoform in mast cells.

IL-4 is a pleiotropic cytokine that signals through STAT6 to direct the transactivation of multiple gene targets. In this study, we demonstrate that mast cells express a distinct STAT6 isoform. This "mast cell STAT" is a product of the STAT6 gene, but is only 65 kDa in size and appears to lack the defined C-terminal transactivation domain. Despite the presence of the conventional 94-kDa STAT6 molecule, it is the smaller isoform that associates with a consensus STAT6 binding site in extracts from IL-4-treated mast cells. This is the first evidence that STAT6 isoforms can be preferentially activated and bind to DNA in a cell-specific manner. These results imply that an additional level of specificity in the IL-4R signaling mechanism exists and may partially explain the diverse effects that IL-4 exerts on different cell types.

Flanking sequences for the human intercellular adhesion molecule-1 NF-kappaB response element are necessary for tumor necrosis factor alpha-induced gene expression.

The regulated expression of intercellular adhesion molecule-1 (ICAM-1) by cytokines such as tumor necrosis factor alpha (TNF-alpha) plays an important role in inflammation and immune responses. Induction of ICAM-1 gene transcription by TNF-alpha has previously been shown to be dependent upon a region of the ICAM-1 5'-flanking sequences that contains a modified kappaB site. We demonstrate here that this modified kappaB site alone is insufficient for induction of transcription by TNF-alpha. Site-directed mutagenesis of both the kappaB site and specific flanking nucleotides demonstrates that both the specific 5'- and 3'-flanking sequences and the modified kappaB site are necessary for TNF-alpha induction. Further, site-directed mutagenesis of this modified kappaB site to a consensus kappaB site allows it to mediate transcriptional activation in response to TNF-alpha, even in the absence of specific flanking sequences. Transcription through this minimal ICAM-1 TNF-alpha-responsive region can be driven by co-expression of p65, and the minimal response element interacts with p65 and p50 in supershift mobility shift assays. However, when in vitro transcription/translation products for the Rel proteins are used in an electrophoretic mobility shift assay, only p65 is capable of binding the minimal response element while both p50 and p65 bind a consensus kappaB oligonucleotide. Additionally, in the absence of the specific flanking nucleotides, the ICAM-1 kappaB site is incapable of DNA-protein complex formation in both electrophoretic mobility shift assay and UV cross-linking/SDS-polyacrylamide gel electrophoresis analysis. These results demonstrate the requirement for specific flanking sequences surrounding a kappaB binding site for functional transcription factor binding and transactivation and TNF-alpha-mediated induction of ICAM-1.

The inflammatory/immune response in critical illness: role of the systemic inflammatory response syndrome.

The inflammatory/immune response is designed to protect the body and limit the extent of injury. In the setting of critical illness, however, regulation of this exquisite response is often lost for reasons that remain to be elucidated. Loss of regulation combined with shock, infection, inflammation, and/or ischemia often leads to the development of the systemic inflammatory response syndrome (SIRS), which frequently is associated with the development of septic shock, disseminated intravascular coagulation (DIC), multiple organ dysfunction (MODS), and other complications of critical illness.

Mediators of coagulation and inflammation: relationship and clinical significance.

Inflammation and coagulopathies are currently thought to play a role in the pathogenesis and pathophysiology of many forms of critical illness, particularly sepsis, multiple organ dysfunction, DIC, and reperfusion injury. Because much of the new pharmacologic research and therapy focuses on inflammation and coagulation mechanisms, it is imperative for the critical care nurse to have a basic understanding of these two complex mechanisms to intelligently and safely administer these drugs and to increase his or her understanding of the disease process and its manifestations. This article will provide an overview of the significant features of inflammation and coagulation and their close relationship. Major clinical syndromes affecting the critical care population will then be described relative to these inflammatory and coagulation events.