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Dendritic cells (DC) are known to be essential immune cells in innate immunity and in the initiation of adaptive immunity. The shaping of adaptive immunity by innate immunity is dependent on DC unique cellular functions and DC-derived effector molecules such as cytokines and chemokines. Thus, it is not surprising that numerous studies have identified alterations in DC number, function, and subset ratios in various diseases, such as infections, cancers, and autoimmune diseases. Recent evidence has also identified that immunosuppression occurring after severe systemic inflammation, such as found in sepsis, is a result of depletion in DC numbers and a later dysfunction in DC activity. This correlation suggests that the sustained DC dysfunction initiated by life-threatening inflammation may contribute to the subsequent immunoparalysis, potentially as a result of the long-term maintenance of an abnormal gene expression pattern. In this review, we summarized the present information regarding altered DC function after a severe, acute inflammatory response and propose a mechanism, whereby epigenetic changes can influence long-term gene expression patterns by DC, thus supporting an immunosuppression phenotype.

This study examined the cell-to-cell interaction between fibroblasts and macrophages as a possible contributor to the chronic inflammatory state. In a coculture system, consisting of macrophages layered over confluent fibroblasts, there was a significant increase in macrophage inflammatory protein 1α (MIP-1α) compared with control cultures. ICAM-1 adhesion was identified as an important stimulus of MIP-1α production by using ICAM-1-specific monoclonal antibodies. Furthermore, fibroblasts from ICAM-1 knockout mice induced significantly less MIP-1α production from peritoneal macrophages when compared to control fibroblasts. In addition, it appeared that oxygen radicals functioned as activating molecules during cellular interaction and production of MIP-1α, as the addition of the antioxidant N-acetylcysteine (NAC) prevented MIP-1α secretion. Thus, the ICAM-1 and oxygen radical-mediated induction of MIP-1α associated with a macrophage/fibroblast coculture system provides one possible mechanism by which immune/inflammatory cell interactions may augment chemokine production and exacerbate chronic inflammatory diseases. J. Leukoc. Biol. 64: 636–641; 1998.

Although many studies have characterized soluble factors that stimulate or inhibit chemokine secretion, in this review we focus on the event of cellular adhesion as a novel mechanism for stimulating chemokine expression. Recent work has demonstrated chemokine expression following cell-to-cell and cell-to-matrix adhesion. The specificity of this finding was demonstrated utilizing various techniques that illustrate that adhesion, and not a soluble stimulus, is in some cases responsible for initiating or augmenting chemokine expression. For example, co-cultures of peripheral blood monocytes and endothelial cells secreted elevated levels of IL-8 and MCP-1 compared with either cell type alone. When co-cultured in transwells, this effect was significantly attenuated. In other experiments, neutralizing monoclonal antibodies to various adhesion molecules inhibited chemokine expression. The effects of adhesion were not limited to leukocytes. Both immune and non-immune cell types were evaluated as potential sources of adhesion-mediated chemokine expression. Not suprisingly, expression of some chemokines was associated with adhesion, whereas others were not, supporting the notion that adhesion differentially signals chemokine secretion during the inflammatory response. We hypothesize that as a recruited leukocyte encounters different adhesion substrates such as endothelial cells, basement membrane, extracellular matrix, and fibroblasts, the expression of chemokines from both the leukocyte and the substrate may be initiated, inhibited, or augmented. Careful characterization of the contribution of adhesion to regulation of chemokine expression will provide insight into the pathogenesis of many human diseases where chemokines have a central role.

The production of eosinophil-specific chemotactic factors during allergic airway responses may be a pivotal event resulting in eosinophil accumulation, activation, and airway damage. Recent studies have identified specific chemokines that may play crucial roles in recruitment of eosinophils to the site of allergic reactions. In this study we have utilized an established model of schistosome egg antigen (SEA)-mediated allergic responses to examine the role of specific C-C chemokines [macrophage inflammatory protein-1α (MIP-1α), RANTES, and monocyte chemoattractant protein-1 (MCP-1)] in eosinophil recruitment. We have previously identified a role for MIP-1α in eosinophil accumulation in the lung and airway during allergic airway inflammation. We extend those studies using in vitro eosinophil chemotaxis to establish that both MIP-1α and RANTES are potent eosinophil chemotactic factors in lungs during allergic airway responses. Morphometric analysis demonstrated a peribronchial accumulation of eosinophils within the lungs beginning at 8 h, peaking at 24 h, and plateauing at 48–96 h after allergen (SEA) challenge. Utilizing whole-lung homogenates from allergen-challenged mice, in vitro eosinophil chemotactic assays demonstrated significant increases in eosinophil chemotactic activity with 8-h lung homogenates and peak activity with samples from 24-h lung homogenates. These data correlated with the morphometric analysis of peribronchial eosinophil accumulation in situ. When lung homogenates from allergen-challenged mice were preincubated in vitro with antibodies specific for MIP-1α, RANTES, or MCP-1, a significant reduction in eosinophil chemotaxis was observed with only MIP-1α and RANTES neutralization. Altogether, these studies indicate that RANTES and MIP-1α are major eosinophil chemotactic factors produced during allergic airway responses.

Effective host defense against bacterial invasion is characterized by the vigorous recruitment and activation of inflammatory cells, which is dependent on the coordinated expression of both pro-and anti-inflammatory cytokines. In this review, we present evidence indicating that both C-X-C and C-C chemokines are integral components of antibacterial host defense. Specifically, in vitro studies indicate that C-X-C chemokines [interleukin-8 (IL-8) and macrophage inflammatory protein 2 (MIP-2)] and the C-C chemokine macrophage inflammatory protein 1 alpha (MIP-1α) augment the ability of polymorphonuclear leukocytes (PMNs) and alveolar macrophages, respectively, to phagocytose and kill Escherichia coli. In addition, the intratracheal instillation of Klebsiella pneumoniae in CD-I mice results in time-dependent production of MIP-2 and MIP-1α, and the inhibition of MIP-2 bioactivity in vivo results in decreases in lung PMN influx, impaired bacterial clearance, and early mortality. Finally, the anti-inflammatory cytokine interleukin-10 (IL-10) is also expressed within the lung during the evolution of Klebsiella pneumonia, and neutralization of IL-10 in vivo results in enhanced proinflammatory cytokine production, bacterial clearance, and increases in both short- and long-term survival. In conclusion, our studies indicate that specific chemokines are important mediators of leukocyte recruitment and/or activation in bacterial pneumonia and that the expression of these chemokines is regulated by endogenously produced IL-10.

Rheumatoid arthritis (RA) is an autoimmune disease characterized by the elicitation and activation of a number of leukocyte populations within both the synovial space and joint tissue. The recruited leukocytes subsequently play an instrumental role in synovial cell proliferation, pannus formation, and bone erosion. Although it is known that leukocytes are important participants in the evolving joint pathology, the mechanism responsible for the successful elicitation of cells to the joint is not clear. A number of studies have identified an association of specific cytokines, including chemokines, with active arthritis, but longitudinal analyses of cytokine expression and the causal role of these mediators have not been defined. Animal models and cell culture systems have proved useful in identifying the expression of various cytokines during the maintenance of chronic joint inflammation. In addition, animal models have provided important information regarding the kinetic production and contribution of specific mediators to the development of experimental arthritis. These studies provide insight into the potential mechanisms for leukocyte involvement in inflammatory joint disease.

The two chemotactic cytokines interleukin-8 (IL-8) and epithelial neutrophil activating protein 78 (ENA-78) were recently shown to be potent chemoattractants and activators of neutrophil function and to be present in certain inflammatory diseases. We have studied the effects of recombinant and natural interferon-α (IFN-α) and of recombinant interferon gamma (rIFN-γ) on the production of EL-8 and ENA-78 in lipopolysaccharide- and interleukin-1–stimulated human monocytes. Both types of interferons showed a strong, concentration-dependent inhibition of neutrophil-stimulating bioactivity. Similarly, the secretion of IL-8 and ENA-78 was also inhibited by up to 73%. Northern blot experiments demonstrated that IFN-α decreases the steady-state levels of IL-8 and ENA-78 mRNA in monocytes, suggesting that IFN-α as well as IFN-γ may control the expression of neutrophil chemotactic cytokines at the mRNA level. J. Leukoc. Biol. 57: 929–935; 1995.

Pulmonary fibrosis is the end point of a chronic inflammatory process characterized by leukocyte recruitment and activation, fibroblast proliferation, and increased extracellular matrix production. Previous studies of models of pulmonary fibrosis have investigated the role of cytokines in the evolution of the fibrotic response. The involvement of tumor necrosis factor and interleukin-1 in bleomycin-induced lung injury, a model of idiopathic pulmonary fibrosis, has been well established, suggesting that cytokines mediate the initiation and maintenance of chronic inflammatory lesions. However, the aforementioned cytokines alone cannot account for the recruitment and activation of specific leukocyte populations found in the bleomycin model. Recently, a family of novel proinflammatory cytokines (chemokines) was cloned and characterized, yielding many putative mediators of leukocyte functions. Macrophage inflammatory protein-1α (MIP-1α) and monocyte chemoattractant protein-1 (MCP-1) belong to the C-C chemotactic cytokine family, a group of low-molecular-weight peptides. These molecules modulate chemotaxis, proliferation, and cytokine expression in leukocyte subsets. Our group has investigated the roles of MCP-1 and MIP-1α in the bleomycin model. Both MCP-1 and MIP-1α are expressed in a time-dependent manner after bleomycin challenge, and passive immunization of these animals with either anti-MIP-1α or anti-MCP-1 antibodies attenuated leukocyte accumulation. In addition, we have identified specific cell types expressing MCP-1 or MIP-1α by in situ hybridization and immunohistochemical localization, respectively. Furthermore, our results indicate that MIP-1α expression is mediated by alveolar macrophage-derived tumor necrosis factor, identifying an important cytokine pathway in the initiation of pulmonary fibrosis. Finally, anti-MIP-1α therapy attenuated fibrosis, providing direct evidence for its involvement in fibrotic pathology. Our work has clearly established that the C-C chemokines MCP-1 and MIP-1α are expressed and contribute to the initiation and maintenance of the bleomycin-induced pulmonary lesion. J. Leukoc. Biol. 57: 782–787; 1995.

SUMMARYThis study examined the relationship ofIL-4, IL-10 and IFN-γ with regard to the local granuloma (GR) and draining lymph node (LN) response to Schistosoma mansoni eggs. Synchronized GR were induced in naive and schistosome-infected mice at the vigorous (8 weeks) and late chronic (20 weeks) stages. In LN cultures, IL-10 and IFN production peaked on day 4 and was greatest for 8 week-infected mice. All GR cultures contained IFN, but compared with naive mice IL-10 production was accelerated at 8 weeks and abrogated at 20 weeks, consistent with expansion and abatement of Th2 activity, Cytokine neutralization was performed in egg-challenged, naive mice that were adoptively sensitized with lymphoid cells from 8 week-infected donors. GR size, GR macrophage tumour necrosis factor (TNF) production and egg antigen-elicited IL-2, IL-4, IL-5, IL-10 and IFN were examined on day 4 of GR formation, Anti-IFN augmented GR area by 40%, increased local IL-4 and IL-10, but decreased IFN and TNF production. In corresponding LN cultures, IFN decreased by about 50%, while IL-2, IL-4, IL-IO and lL-5 increased by nearly two-, four-, five- and six-fold, respectively, Anti-IL-10 did not affect GR size or GR cytokines, but increased IFN levels in LN cultures four-fold and decreased IL-2, IL-4, lL-5 and IL-10. Anti-IL-4 abrogated GR area by 40%, along with a reduction in local IL-4 and TNF production. In LN, IL-4 depletion reduced IL-4 and IL-5 by 60–70% and increased IFN levels. These results support the notion of a cross-regulatory network in which IFN inhibits Th2 and IL-10 inhibits ThI cells. IL-4 fosters Th2 cell differentiation in LN, but also performs a critical recruitment function in the eosinophil-rich schistosome egg-induced GR, whereas IFN contributes to enhanced GR macrophage function.

The accumulation of polymorphonuclear cells (PMN) in tissue is an essential element of the inflammatory response that is important in host defense. Adherence to endothelium constitutes the first step in PMN migration from the vascular compartment to the interstitium. We demonstrate that human peripheral blood mononuclear cells (PBMC) adherent to plastic can result in expression of interleukin-8 (IL-8), a potent PMN chemoattractant and activating cytokine. Northern blot analyses showed PBMC adherent to plastic expressed IL-8 steady-state mRNA levels by 30 min, peaked at 8 h, and then decreased over the next 16 h. In contrast, nonadherent PBMC (cultured in teflon chambers) expressed less than 25% of the maximal IL-8 steady-state mRNA levels as compared with adherent PBMC. Adherent PBMC-associated IL-8 determined by immunohistochemistry, supernatant chemotactic bioactivity, and extracellular antigenic IL-8 paralleled IL-8 mRNA expression. Antigenic and bioactive IL-8 were significantly apparent by 4–8 h, respectively, and increased significantly to maximal levels by 24 h. Furthermore, adherent PBMC IL-8 gene expression was suppressed by either concomitant treatment with actinomycin-D or cycloheximide, yet specific neutralizing antibodies directed against either IL-1β or tumor necrosis factor (TNF)-α failed to alter adherence-induced steady-state IL-8 mRNA levels. These data support the hypothesis that PBMC adherence is an important signal for the production of IL-8, and may be essential to the development of the inflammatory response through the elicrtation of PMN.

To understand the molecular events which are important in leucocyte trafficking in cutaneous inflammation, poison ivy/oak extract was applied topically to the skin, and the simultaneous assessment of a variety of clinical and immunopathological parameters performed. The clinical response of subjects was divided into three main groups: I, 2-24h after application, before the onset of erythema; II, 48 h-1 week after application during maximal clinical changes; III, 2-3 weeks after application when the inflammation had subsided. Six different biopsies per subject were evaluated over the study period and the density of dermal cellular infiltrate, and the distribution of intercellular adhesion molecule-1, (ICAM-1), endothelial leucocyte adhesion molecule-1, (ELAM-1), vascular cell adhesion molecule-1, (VCAM-1), interleukin 8 (IL-8) and tumour necrosis factor-alpha (TNF-alpha), determined. Eight hours after exposure, before lymphocytes and monocytes had entered the dermal interstitium or epidermis, the keratinocytes expressed TNF-alpha and ICAM-1, whilst the endothelial cells expressed ELAM-1, VCAM-1 and ICAM-1. Group II biopsies revealed increasing keratinocyte expression of TNF-alpha and ICAM-1 with the appearance of IL-8, which correlated with the onset of epidermal T-cell trafficking. The endothelium was strongly positive for ELAM-1 and VCAM-1, but there was no influx of neutrophils. Group III biopsies showed a decrease in the expression of ICAM-1, VCAM-1 and ELAM-1 by both keratinocytes and endothelium with a reduction in epidermal/dermal inflammation, although the endothelial cell staining of VCAM-1 and ELAM-1 did not completely disappear. These results suggest that on exposure to poison ivy/oak, keratinocytes rapidly produce TNF-alpha which leads to an early autoinduction of ICAM-1, and later IL-8. There is also a paracrinemediated induction and augmentation of underlying endothelial cell ELAM-1, VCAM-1 and ICAM-1.

The present study examined changes in lipopolysaccharide (LPS)-induced interleukin 1 (IL-1) and tumor necrosis factor (TNF) production by murine peritoneal macrophages during the chronic exudative response to Freund’s complete adjuvant (CFA). Macrophages were isolated by peritoneal lavage and adherence at intervals over a 32 day period following i.p. injection of CFA. Optimal culture conditions for IL-1 and TNF production were predetermined, and it was found that IL-1 production was profoundly impaired at densities of above 150 cells/mm2, whereas TNF sythesis was more resistant to density effects. Using optimal conditions, we observed a sequential appearance of monokines. On day 0 there was minimal IL-1 production and no detectable TNF production. By days 4–7, IL-1 production reached maximum levels with a steady decline to baseline by day 32. TNF production steadily increased after day 2, reached maximal levels by days 16–20, and then partly declined by day 32. These findings were supported by kinetic analyses at specified days. When related to exudative events, it appeared that maximal IL-1 was associated with the recruitment stage of the reaction, whereas TNF production was associated with the established exudate. Immunohistochemical analysis revealed that TNF production could be related to the proportion of macrophages with cytoplasmic TNF expression. In contrast, IL-1α and -1β expression was comparable among populations with 85–100% of cells showing cytoplasmic expression 6 hr after LPS stimulus. Whereas cytoplasmic IL-1α persisted for the 18 hr study period, IL-1β disappeared from many adjuvant recruited cells. Our findings suggest that monokine production is orchestrated during macrophage recruitment and activation at sites of chronic inflammation.

The sequence of events by which bacteria activate immune responses is extremely complex. The culmination of these events often leads to immunopathologic consequences, which are evident in both local and systemic bacterial infections. Where mediators are generated, immune/inflammatory cells are activated, and tissue is destroyed. In the case of acute inflammatory reactions, the following scenario can occur: bacteria activate the complement cascade, polymorphonuclear leukocytes are recruited, and lysosomal enzymes and toxic oxygen products that destroy both the inciting bacteria and the surrounding tissue are generated. The complex interplay among the various mediator systems, inflammatory cells, and toxic products is recognized as a complicated array of pathways necessary for clearance of a given bacterial infection. Understanding these pathways, which ultimately lead to an appropriate immune response to the bacteria, is an extremely challenging problem to microbiologists and immunologists alike.

Prostaglandin E2 (PGE2)-mediated suppression of macrophage interleukin-1 alpha,beta and tumor necrosis factor-alpha synthesis was examined at the cellular and molecular levels. Treatment of lipopolysaccharide (LPS)-stimulated adjuvant-elicited murine macrophages with 5 x 10(-7) M PGE2 caused a 70% reduction in cell-associated TNF but had no suppressive effect on cell-associated interleukin-1 (IL-1) activity. Consistent with this result, Northern blot and nuclear transcription analyses demonstrated suppression of TNF mRNA but PGE2 had no effect on IL-1 alpha and IL-1 beta mRNA accumulation, as compared to LPS controls. Immunoperoxidase staining for cell-associated TNF alpha, IL-1 alpha, and IL-1 beta demonstrated that PGE2 suppressed TNF, but not IL-1 alpha or -beta expression, supporting the bioassay data. These results imply that PGE2-mediated regulation of IL-1 alpha,beta and TNF alpha is quite distinct. Synthesis of TNF appears to be regulated at least at the level of transcription, whereas that for IL-1 alpha and -beta is regulated post-transcriptionally.

The potential involvement of macrophages, T lymphocytes, and the cytokine twnor necrosis factor (TNF) in regression of the corpus hueum was investigated at d(fferent stages of pseudopregnancy and pregnancy by use of immunocytochemical methods and a TNF bioassay. Few macrophages (11± 6per high power field of 8-j.un frozen sections of corpus luteum, Day 10 of pseudopregnancy) were observed until the very end of pseudopregnancy, when the number of macrophages increased greatly (176 ± 42 per high power field, Day 19 ofpseudopregnancy). Pregnancy, of 32 days duration, delayed large-scale macrophage accumulation until 3 days after parturition (154 ± 30 per high powerfield). Low TNF activity (-1.0 U/mg protein) was detected in incubations of luteal tissue ala!! stages; in response to lipopolysaccharide, TNF values in medium increased 10- to 30-fold at times of luzea! regression and macrophage accumulation (1 day postpartum and Day 19 ofpseudopregnancy). Class 11-positive T lymphocytes were observed in luteal tissue, but unlike macrophages, the number of lymphocytes did not increase at the time of regression of the corpus luteum. These data are consistent with the hypothesis that involution of the corpus lutewn is promoted through the interactions of inflammatory cells and action of TNF, although the action of TNF has not been determined in this luteal tissue. Through unknown mechanisms, pregnancy postpones the accu,nulation of macrophages in the corpus luteum, in association with the prolongation of luteal function until