B cell receptors and complement receptors target the antigen to distinct intracellular compartments

The processing of exogenous Ags is an essential step for the generation of immunogenic peptides that will be presented to T cells. This processing relies on the efficient intracellular targeting of Ags, because it depends on the content of the compartments in which Ags are delivered in APCs. Opsonization of Ags by the complement component C3 strongly enhances their presentation by B cells and increases their immunogenicity in vivo. To investigate the role of C3 in the targeting of Ags, we compared the intracellular traffic of proteins internalized by complement receptor (CR) and B cell receptor (BCR) in B lymphocytes. Whereas both receptors are able to induce efficient Ag presentation, their intracellular pathways are different. CR ligand is delivered to compartments containing MHC class II molecules (MHC-II) but devoid of transferrin receptor and Lamp-2, whereas BCR rapidly targets its ligand toward Lamp-2-positive, late endosomal MHC-II-enriched compartments through intracellular vesicles containing transferrin receptor. CR and BCR are delivered to distinct endocytic pathways, and the kinetic evolution of the protein content of these pathways is very different. Both types of compartments contain MHC-II, but CR-targeted compartments receive less neosynthesized MHC-II than do BCR-targeted compartments. The targeting induced by CR toward compartments that are distinct from BCR-targeted compartments probably participates in C3 modulation of Ag presentation.

Effect of pregnancy and human immunodeficiency virus infection on intracellular interleukin-2 production patterns

Human immunodeficiency virus type 1 (HIV-1) infection decreases the production of interleukin-2 (IL-2) from CD4+ and CD8+ T cells. Recombinant IL-2 (rIl-2) has been given to HIV-infected individuals to generate significant increases in CD4+ T-cell counts. There are limited data regarding the effects of pregnancy and HIV infection on IL-2 production in humans. To investigate the effects of human pregnancy, HIV infection, and HIV therapy on IL-2 production, we evaluated 61 women. Intracellular IL-2 production by CD4+ T cells from nonpregnant HIV-infected women was significantly lower than in that in uninfected women (45% +/- 8% versus 52% +/- 8%, P = 0.04). In contrast, there was no difference in levels of intracellular IL-2 production between HIV-infected and uninfected pregnant women. These observations suggest that pregnancy may down-regulate IL-2 production regardless of HIV infection status. Future studies should evaluate IL-2 production patterns in larger cohorts of women so that the physiological significance of IL-2 down-regulation in pregnancy can be further evaluated. This information is essential to assess the possible use of IL-2 supplementation therapy as a means of enhancing immune responses among HIV-infected pregnant women.

Analysis of protein phosphorylation and cellular signaling events by flow cytometry: techniques and clinical applications

Analysis of protein phosphorylation with flow cytometric techniques has emerged as a powerful tool in the field of immunological signaling, allowing cellular subsets in complex populations to be analyzed accurately and rapidly. In this review, we examine the development of phospho-epitope, or phospho-specific, flow cytometry and the premises upon which the technique is based. Phospho-specific flow cytometry is compared to traditional biochemical methods, and its advantages, such as single cell analysis, multiparameter data acquisition, rapid protocols, and the ability to analyze rare cell subsets, are detailed. We also discuss the many technical considerations that must be addressed when developing new antibodies or analyzing new epitopes including antigen accessibility, stability of the phospho-epitope, fluorophore selection, surface phenotype integrity, and antibody suitability for staining epitopes inside fixed and permeabilized cells. The methods that have been used to date are described in light of these technical considerations. The importance of developing bioinformatic platforms in parallel with these techniques is emphasized due to the large, multiparameter datasets that are rapidly accumulated and which require more efficient data viewing and complex clustering methods than currently available for flow cytometric data. Finally, we discuss the potential clinical applications of phospho-specific flow cytometry in analyzing immune cell development and antigen-specific immune responses, as well as pharmacodynamic profiling of disease states or drug efficacy and specificity against particular signaling proteins.

Expression of CD154 (CD40 ligand) by human lung fibroblasts: differential regulation by IFN-gamma and IL-13, and implications for fibrosis

The CD40-CD40 ligand (CD40L) system (CD154) is a central means of immune cell communication crucial for Ig class switching and enhanced Ag presentation. CD40 is also a key signaling conduit to activate nonhematopoietic cells, such as fibroblasts and endothelial cells, to produce proinflammatory mediators. Disruption of the CD40-CD40L pathway reduces lung inflammation and fibrosis, autoimmune disease and atherosclerosis. Non-bone marrow-derived structural cells are not known to express CD40L. In this study, we reveal the intriguing finding that primary strains of human lung fibroblasts derived from normal and scarred lung express both CD40L mRNA and protein. Interestingly, CD40L expression is down-regulated by IFN-gamma, a type 1 cytokine with antiscarring properties, and is up-regulated by the profibrogenic type 2 cytokine IL-13. Flow cytometry and laser confocal microscopy revealed that the majority of CD40L was located intracellularly. Importantly, fibroblast strains from human idiopathic pulmonary fibrosis tissue expressed increased levels of CD40L compared with fibroblasts from nonscarred lung. Fibroblasts in the scarred areas of human lung tissue expressed high levels of CD40L. Finally, the blood and lung lavage levels of CD40L are significantly elevated in fibrosis patients compared with normals. These new findings demonstrate that fibroblasts are a new source of CD40L and that those involved in scarring may have undergone a selected expansion for high CD40L expression. Moreover, the antifibrotic activity of IFN-gamma may involve the down-regulation of fibroblast CD40L levels. We speculate that fibroblast-derived CD40L plays a role in promoting fibroblast activation and possibly in interaction with CD40 bearing cells.

CTLA-4 Blockage Increases Resistance to Infection with the Intracellular ProtozoanTrypanosoma cruzi

Recent studies have revealed an important role for CTLA-4 as a negative regulator of T cell activation. In the present study, we evaluated the importance of CTLA-4 to the immune response against the intracellular protozoan, Trypanosoma cruzi, the causative agent of Chagas' disease. We observed that the expression of CTLA-4 in spleen cells from naive mice cultured in the presence of live trypomastigote forms of T. cruzi increases over time of exposure. Furthermore, spleen cells harvested from recently infected mice showed a significant increase in the expression of CTLA-4 when compared with spleen cells from noninfected mice. Blockage of CTLA-4 in vitro and/or in vivo did not restore the lymphoproliferative response decreased during the acute phase of infection, but it resulted in a significant increase of NO production in vivo and in vitro. Moreover, the production of IFN-gamma in response to parasite Ags was significantly increased in spleen cells from anti-CTLA-4-treated infected mice when compared with the production found in cells from IgG-treated infected mice. CTLA-4 blockade in vivo also resulted in increased resistance to infection with the Y and Colombian strains of T. cruzi. Taken together these results indicate that CTLA-4 engagement is implicated in the modulation of the immune response against T. cruzi by acting in the mechanisms that control IFN-gamma and NO production during the acute phase of the infection.

NK cells regulate CD8+ T cell effector function in response to an intracellular pathogen

We studied the role of NK cells in regulating human CD8+ T cell effector function against mononuclear phagocytes infected with the intracellular pathogen Mycobacterium tuberculosis. Depletion of NK cells from PBMC of healthy tuberculin reactors reduced the frequency of M. tuberculosis-responsive CD8+IFN-gamma+ cells and decreased their capacity to lyse M. tuberculosis-infected monocytes. The frequency of CD8+ IFN-gamma+ cells was restored by soluble factors produced by activated NK cells and was dependent on IFN-gamma, IL-15, and IL-18. M. tuberculosis-activated NK cells produced IFN-gamma, activated NK cells stimulated infected monocytes to produce IL-15 and IL-18, and production of IL-15 and IL-18 were inhibited by anti-IFN-gamma. These findings suggest that NK cells maintain the frequency of M. tuberculosis-responsive CD8+IFN-gamma+ T cells by producing IFN-gamma, which elicits secretion of IL-15 and IL-18 by monocytes. These monokines in turn favor expansion of Tc1 CD8+ T cells. The capacity of NK cells to prime CD8+ T cells to lyse M. tuberculosis-infected target cells required cell-cell contact between NK cells and infected monocytes and depended on interactions between the CD40 ligand on NK cells and CD40 on infected monocytes. NK cells link the innate and the adaptive immune responses by optimizing the capacity of CD8+ T cells to produce IFN-gamma and to lyse infected cells, functions that are critical for protective immunity against M. tuberculosis and other intracellular pathogens.

Intracellular regulation of Fas-induced apoptosis in human fibroblasts by extracellular factors and cycloheximide

Fibroblasts play an important role in reparative and inflammatory processes by synthesizing extracellular matrix components and releasing growth factors and cytokines. Fibroblast apoptosis has been observed at the termination phase of reparative or fibrotic responses, but its regulation in this context is poorly known. We investigated the susceptibility of human dermal fibroblasts (DF) to Fas-induced apoptosis and its regulation by extracellular factors potentially involved in immune-mediated inflammation and repair. DF expressed all components of the Fas apoptotic pathway: surface Fas, Fas-associated protein with death domain, and caspase-8 proteins. However, Fas activation resulted in caspase-8 activation and apoptosis only in the presence of cycloheximide (CHX). DF constitutively expressed Fas-associated death domain-like IL-1-converting enzyme-like inhibitory protein (FLIP) that was drastically down-regulated by CHX. Exogenous growth factors, cytokines, and adherence to the extracellular matrix shifted the balance of FLIP-caspase-8 proteins and modified the susceptibility of DF to Fas- or Fas-CHX-induced apoptosis. Short-term serum deprivation, suspension culture, and pretreatment with IFN-gamma or TNF-alpha increased, whereas long-term serum-free culture and pretreatment with TGF-beta or IL-10 decreased the apoptotic susceptibility of DF. Surface Fas expression was only modified by TNF-alpha and IFN-gamma, whereas all studied factors modified FLIP-caspase-8 protein expression, consistently with their pro- or antiapoptotic effects. Antisense FLIP oligonucleotides prevented resistance to Fas-induced apoptosis in DF. FLIP-caspase-8 balance seems tightly regulated in fibroblasts by extracellular factors that determine their susceptibility to Fas- or Fas-CHX-induced apoptosis. Th1 and Th regulatory cytokines display opposite effects on fibroblast apoptosis that suggest that their pro- or antifibrotic effects involve direct effects on fibroblast survival.

STAT1 plays a critical role in the regulation of antimicrobial effector mechanisms, but not in the development of Th1-type responses during toxoplasmosis

The production of IFN-gamma by T cells and the ability of this cytokine to activate the transcription factor STAT1 are implicated in the activation of antimicrobial mechanisms required for resistance to intracellular pathogens. In addition, recent studies have suggested that the ability of STAT1 to inhibit the activation of STAT4 prevents the development of Th1 responses. However, other studies suggest that STAT1 is required to enhance the expression of T-bet, a transcription factor that promotes Th1 responses. To address the role of STAT1 in resistance to T. gondii, Stat1-/- mice were infected with this pathogen, and their response to infection was assessed. Although Stat1-/- mice produced normal serum levels of IL-12 and IFN-gamma, these mice were unable to control parasite replication and rapidly succumbed to this infection. Susceptibility to toxoplasmosis was associated with an inability to up-regulate MHC expression on macrophages, defects in NO production, and the inability to up-regulate some of the IFN-inducible GTPase family of proteins, molecules associated with antitoxoplasma activity. Analysis of T cell responses revealed that STAT1 was not required for the development of a Th1 response, but was required for the infection-induced up-regulation of T-bet. Together these studies suggest that during toxoplasmosis the major role of STAT1 is not in the development of protective T cell responses, but, rather, STAT1 is important in the development of antimicrobial effector mechanisms.

Phenotypes indicating cytolytic properties of Borrelia-specific interferon-gamma secreting cells in chronic Lyme neuroborreliosis

The immuno-pathogenetic mechanisms underlying chronic Lyme neuroborreliosis are mainly unknown. Human Borrelia burgdorferi (Bb) infection is associated with Bb-specific secretion of interferon-gamma (IFN-gamma), which may be important for the elimination of Bb, but this may also cause tissue injury. In order to increase the understanding of the pathogenic mechanisms in chronic neuroborreliosis, we investigated which cell types that secrete IFN-gamma. Blood mononuclear cells from 13 patients with neuroborreliosis and/or acrodermatitis chronicum atrophicans were stimulated with Bb antigen and the phenotypes of the induced IFN-gamma-secreting cells were analyzed with three different approaches. Cells expressing CD8 or TCRgammadelta, which both have cytolytic properties, were the main phenotypes of IFN-gamma-secreting cells, indicating that tissue injury in chronic neuroborreliosis may be mediated by cytotoxic cells.

Cutting Edge: Innate Immune System Discriminates between RNA Containing Bacterial versus Eukaryotic Structural Features That Prime for High-Level IL-12 Secretion by Dendritic Cells

RNA derived from bacterial but not eukaryotic sources, when transfected into human monocyte-derived dendritic cell precursors, induces high-level IL-12 secretion in conjunction with dendritic cell maturation stimuli. In vitro-transcribed mRNA that mimics the structure of bacterial mRNA in the lack of a long 3'-poly(A) tail likewise induces IL-12 secretion, but this property is lost upon efficient enzymatic 3'-polyadenylation. Among other tested RNAs, only polyuridylic acid induced IL-12 p70. This RNA response phenomenon appears biologically distinct from the classically defined response to dsRNA. RNA-transfected APC also polarize T cells in an IL-12-dependent manner toward the IFN-gamma(high)IL-5 (low) Th1 phenotype, suggesting a link between the detection of appropriately structured RNA and the skewing of immune responses toward those best suited for controlling intracellular microbes. RNA structured to emulate bacterial patterns constitutes a novel vaccine strategy to engender polarized Th1-type immune responses.

Outer membrane protein A from Klebsiella pneumoniae activates bronchial epithelial cells: implication in neutrophil recruitment

Aside from its mechanical barrier function, bronchial epithelium plays an important role both in the host defense and in the pathogenesis of inflammatory airway disorders. To investigate its role in lung defense, the effect of a bacterial cell wall protein, the outer membrane protein A from Klebsiella pneumoniae (kpOmpA) on bronchial epithelial cells (BEC) was evaluated on adhesion molecule expression and cytokine production. Moreover, the potential implication of this mechanism in kpOmpA-induced lung inflammation was also determined. Our in vitro studies demonstrated that kpOmpA strongly bound to BEAS-2B cells, a human BEC line, and to BEC primary cultures, resulting in NF-kappaB signaling pathway activation. Exposure to kpOmpA increased ICAM-1 mRNA and cell surface expression, as well as the secretion of IL-6, CXC chemokine ligand (CXCL)1, CXCL8, C-C chemokine ligand 2, CXCL10 by BEAS-2B cells, and BEC primary cultures (p < 0.005). We analyzed in vivo the consequences of intratracheal injection of kpOmpA to BALB/c mice. In kpOmpA-treated mice, a transient neutrophilia (with a maximum at 24 h) was observed in bronchoalveolar lavage and lung sections. In vivo kpOmpA priming induced bronchial epithelium activation as evaluated by ICAM-1 and CXCL1 expression, associated with the secretion of CXCL1 and CXCL5 in bronchoalveolar lavage fluids. In the lung, an increased level of the IL-6, CXCL1, CXCL5, CXCL10 mRNA was observed with a maximum at 6 h. These data showed that kpOmpA is involved in host defense mechanism by its ability to activate not only APC but also BEC, resulting in a lung neutrophilia.

Surface translocation of pactolus is induced by cell activation and death, but is not required for neutrophil migration and function

Pactolus is a cell surface protein expressed by murine neutrophils. Pactolus is similar to the beta integrins, except it lacks a functional metal ion-dependent adhesion site domain and is expressed without an alpha-chain partner. The majority of the Pactolus protein is held within the cell in dense granules in a highly glycosylated form. This intracellular form of Pactolus can be released to the cell surface following inflammatory activation or ligation of Pactolus on the cell surface. In addition, intracellular Pactolus translocates to the neutrophil surface following induction of apoptosis. Neutrophil activation studies suggest that Pactolus does not serve as an activating or phagocytic receptor for the neutrophil. To further define the function of Pactolus, a Pactolus-null mouse was generated. Pactolus-deficient animals mature appropriately and possess normal numbers of neutrophils, display appropriate migration into sites of inflammation, and combat introduced infections efficiently. These data suggest that Pactolus does not function as a neutrophil phagocytic or adhesion receptor, but may instead serve as a sugar-bearing ligand for lectin recognition by other cells.

IL-15 and cognate antigen successfully expand de novo-induced human antigen-specific regulatory CD4+ T cells that require antigen-specific activation for suppression

An important prerequisite in using regulatory T cells for immunotherapy is their ex vivo expansion without loss of suppressor function. Human anergic regulatory T cells are expandable by Ag-specific stimulation in the presence of IL-2. IL-15, like IL-2, is a T cell growth factor that, in contrast to IL-2, stimulates survival of T cells. In this study, we examined whether IL-15 could be exploited as a superior growth factor of human CD4(+) anergic regulatory T cells that were generated by costimulation blockade. Next, IL-15, as compared with IL-2, was investigated with respect to expansion and function of these regulatory T cells. Optimal expansion required cognate allogeneic stimulation in the presence of exogenous IL-15. IL-15 resulted in enhanced survival that was paralleled by an increased number of Bcl-2-expressing cells. Moreover, IL-15 induced a distinct type of anergy characterized by hyperreactivity to IL-15, resulting in improved expansion. This is likely attributed to increased propensity of these cells to up-regulate both alpha- and gamma-chains of the IL-2 and IL-15 receptor. Notably, IL-15-expanded regulatory CD4(+) T cells suppressed both naive and memory T cells in a superior way. Immunosuppression required alloantigen-specific stimulation and appeared gamma-irradiation resistant and independent of IL-10, TGFbeta, or CTLA-4 interactions. These regulatory T cells were stable suppressors, mediating bystander suppression upon TCR stimulation, but leaving recall responses unaffected in the absence of cognate Ag. Finally, human naturally occurring regulatory CD4(+)CD25(+) T cells appeared important in generating regulatory T cells by costimulation blockade. In conclusion, IL-15-expanded, de novo-induced human anergic regulatory CD4(+) T cells are of interest in Ag-specific immunotherapy.

Soluble forms of Toll-like receptor (TLR)2 capable of modulating TLR2 signaling are present in human plasma and breast milk

Dysregulation of the initial, innate immune response to bacterial infection may lead to septic shock and death. Toll-like receptors (TLRs) play a crucial role in this innate immune response, and yet the regulatory mechanisms controlling microbial-induced TLR triggering are still to be fully understood. We have therefore sought specific regulatory mechanisms that may modulate TLR signaling. In this study, we tested for the possible existence of a functionally active soluble form of TLR2. We demonstrated the existence of natural soluble forms of TLR2 (sTLR2), which we show to be capable of modulating cell activation. We found that blood monocytes released sTLR2 constitutively and that the kinetics of sTLR2 release increased upon cell activation. Analysis of cells expressing the human TLR2 cDNA or its c-myc-tagged version indicated that sTLR2 resulted from the posttranslational modification of the TLR2 protein in an intracellular compartment. Moreover, an intracellular pool of sTLR2 is maintained. sTLR2 was found naturally expressed in breast milk and plasma. Milk sTLR2 levels mirrored those of the TLR coreceptor soluble CD14. Depletion of sTLR2 from serum resulted in an increased cellular response to bacterial lipopeptide. Notably, serum sTLR2 was lower in tuberculosis patients. Coimmunoprecipitation experiments and computational molecular docking studies showed an interaction between sTLR2 and soluble CD14 in plasma and milk. These findings suggest the existence of a novel and specific innate immune mechanism regulating microbial-induced TLR triggering, and may lead to new therapeutics for the prevention and/or treatment of severe infectious diseases.

Increased Dendritic Cell Numbers Impair Protective Immunity to Intracellular Bacteria Despite Augmenting Antigen-Specific CD8+T Lymphocyte Responses

Dendritic cells (DCs) reside in tissues, where they function as sentinels, providing an essential link between innate and adaptive immunity. Increasing the numbers of DCs in vivo augments T cell responses, and can cause dramatic CTL-dependent tumor regression. To determine whether greater DC numbers promoted T cell-mediated protection in the context of host defense against intracellular bacteria, we treated mice with Flt3 ligand (Flt3-L) to increase DCs in vivo and challenged them with Listeria monocytogenes. Unexpectedly, after primary challenge with Listeria, the overall control of Listeria infection was impaired in Flt3-L-treated mice, which had greater bacterial burden and mortality than controls. Similar results were obtained when DC numbers were increased by treatment with polyethylene glycol-conjugated GM-CSF rather than Flt3-L and in mice infected with Mycobacterium tuberculosis. Impaired protection was not due to dysfunctional T cell responses, as Flt3-L-treated mice had a greater frequency and absolute number of Ag-specific CD8+ T cells, which produced IFN-gamma, exhibited cytolytic activity, and transferred protection. The increased Listeria burden in Flt3-L-treated mice was preferentially associated with DCs, which were unable to kill Listeria and more resistant to CTL lysis compared with macrophages in vitro. Although we cannot exclude the possibility that other potential effects, in addition to increased numbers of DCs, are shared by Flt3-L and polyethylene glycol-conjugated GM-CSF and contributed to the increase in susceptibility observed in treated mice, these results support the notion that DC numbers must be properly controlled within physiological limits to optimize host defense to intracellular bacterial pathogens.

Lipopolysaccharide fromCoxiella burnetiiIs Involved in Bacterial Phagocytosis, Filamentous Actin Reorganization, and Inflammatory Responses through Toll-Like Receptor 4

The role of Toll-like receptors (TLRs) in the recognition of extracellular and facultative intracellular bacteria by the innate immune system has been extensively studied, but their role in the recognition of obligate intracellular organisms remains unknown. Coxiella burnetii, the agent of Q fever, is an obligate intracellular bacterium that specifically inhabits monocytes/macrophages. We showed in this study that C. burnetii LPS is involved in the uptake of virulent organisms by macrophages but not in that of avirulent variants. The uptake of virulent organisms was dependent on TLR4 because it was reduced in macrophages from TLR4(-/-) mice. In addition, LPS was responsible for filamentous actin reorganization induced by virulent C. burnetii, which was prevented in TLR4(-/-) macrophages. In contrast, the intracellular fate of C. burnetii was not affected in TLR4(-/-) macrophages, suggesting that TLR4 does not control the maturation of C. burnetii phagosome and the microbicidal activity of macrophages. These results are consistent with in vivo experiments because the pattern of tissue infection and the clearance of C. burnetii were similar in wild-type and TLR4(-/-) mice. We also showed that the number of granulomas was decreased in the liver of infected TLR4(-/-) mice, and the formation of splenic granulomas was only transient. The impaired formation of granulomas was associated with decreased production of IFN-gamma and TNF. Taken together, these results demonstrate that TLR4 controls early events of C. burnetii infection such as macrophage phagocytosis, granuloma formation, and cytokine production.

Fc epsilon RI signaling of mast cells activates intracellular production of hydrogen peroxide: role in the regulation of calcium signals

Earlier studies, including our own, revealed that activation of mast cells is accompanied by production of reactive oxygen species (ROS) that help to mediate the release of the inflammatory mediators, including histamine and eicosanoids. However, little is known about the mechanisms of ROS production, including the species of oxidants produced. In this study we show that in both the RBL-2H3 mast cell line and bone marrow-derived mast cells, FcepsilonRI cross-linking stimulates intracellular oxidative burst, including hydrogen peroxide (H(2)O(2)) production, as defined with the oxidant-sensitive dyes dichlorofluorescein and scopoletin and the selective scavenger ebselen (2-phenyl-1,2-benzisoselenazol-3(2H)-one). The oxidative burst was observed immediately after stimulation and was most likely due to an NAD(P)H oxidase. Experiments using selective pharmacological inhibitors demonstrated that activation of tyrosine kinases and phosphatidylinositol-3-kinase is required for induction of the oxidative burst. Blockade of the oxidative burst by diphenyleneiodonium impaired the release of preformed granular mediators, such as histamine and beta-hexosaminidase, and the secretion of newly synthesized leukotriene C(4), whereas selective scavenging H(2)O(2) by ebselen impaired leukotriene C(4) secretion, but not degranulation. Sustained elevation of cytosolic calcium through store-operated calcium entry was totally abolished when ROS production was blocked. In contrast, selective depletion of H(2)O(2) caused a considerable decrease and delay of the calcium response. Finally, tyrosine phosphorylation of phospholipase Cgamma and the linker for activation of T cells, an event required for calcium influx, was suppressed by diphenyleneiodonium and ebselen. These studies demonstrate that activation of the intracellular oxidative burst is an important regulatory mechanism of mast cell responses.

Platelet-activating factor mediates CD40-dependent angiogenesis and endothelial-smooth muscle cell interaction

The aim of the present study was to investigate whether stimulation of CD40 expressed by endothelial or smooth muscle cells triggers the synthesis of platelet-activating factor (PAF), an inflammatory mediator with angiogenic properties, and whether PAF contributes to CD40-induced neoangiogenesis. The results obtained indicate that the interaction of CD40 with soluble CD154 or with CD154 expressed on the membrane of leukocytes (CD154-transfected J558 cells) or of activated platelets, stimulated the synthesis of PAF by endothelial cells but not by smooth cells. The synthesis of PAF triggered by activated platelets was inhibited by a soluble CD40-murine Ig fusion protein that prevents the interaction between membrane CD40 and CD154. Studies with specific inhibitors and evaluation of protein phosphorylation indicated the involvement in PAF synthesis of two intracellular signaling pathways leading to cytosolic phospholipase A(2) activation: a phospholipase Cgamma-protein kinase C-Raf-p42/p44-mitogen-activated protein kinase (MAPK) and a MAPK kinase-3/6-dependent activation of p38 MAPK. PAF synthesized by endothelial cells after CD40 stimulation was instrumental in the in vitro migration and vessel-like organization of endothelial cells, and in the interaction between endothelial cells and smooth muscle cells, as inferred by the inhibitory effect of two different PAF receptor antagonists, WEB2170 and CV3988. In vivo, blockade of PAF receptors prevented the angiogenic effect triggered by CD40 stimulation in a murine model of s.c. Matrigel implantation. In conclusion, these observations indicate that PAF synthesis induced by stimulation of endothelial CD40 contributes to the formation and organization of new vessels. This may be relevant in the vascular remodeling associated with tumor and inflammatory neoangiogenesis.

Intracellular expression of interleukin-4 and interferon-gamma by a Mycobacterium tuberculosis antigen-stimulated CD4+ CD57+ T-cell subpopulation with memory phenotype in tuberculosis patients

In some chronic pathological conditions, antigen persistence activates and expands the CD4+ CD57+ T-cell subset. The host immune response against tuberculosis infection is maintained through the continuous presence of antigen-stimulated effector/memory helper T cells. To determine whether CD4+ CD57+ T cells were also expanded in human tuberculosis, we analysed (by flow cytometry) the phenotype of peripheral blood CD4+ T cells from 30 tuberculosis patients and 30 healthy controls. We observed a significant increase in the CD4+ CD57+ T-cell subset in tuberculosis patients in comparison to healthy controls (P < 0.001). Most CD4+ CD57+ T cells exhibited a CD28- CD45RO+ CD62L- phenotype, which is associated with memory cells. In vitro, a higher number of antigen-stimulated CD4+ CD57+ T cells produced intracellular interferon-gamma and interleukin-4 compared with antigen-stimulated CD4+ CD57- T cells (P < 0.001). These findings suggest that the majority of CD4+ CD57+ T cells correspond to a phenotype of activated memory T cells.

Cutting Edge: Dendritic Cells Copulsed with Microbial and Helminth Antigens Undergo Modified Maturation, Segregate the Antigens to Distinct Intracellular Compartments, and Concurrently Induce Microbe-Specific Th1 and Helminth-Specific Th2 Responses

To examine the ability of dendritic cells (DC) to discriminate between helminth and microbial Ag and induce appropriately polarized Th responses, mouse DC were copulsed with the helminth Ag, schistosome egg Ag (SEA), along with the bacterium Proprionebacterium acnes, Pa, and transferred into wild-type mice. Strikingly, SEA/Pa-copulsed DC induced concurrent Pa-specific Th1 (but not Th2) responses and SEA-specific Th2 (but not Th1) responses. Although DC exposed to both Ag undergo many of the maturation-associated changes that accompany exposure to Pa alone, Pa-induced IL-12 production was inhibited by SEA. Examination of Ag uptake revealed that SEA and Pa are acquired via discrete pathways and enter nonoverlapping intracellular compartments. Data suggest that segregation of SEA and Pa into distinct compartments, coupled with SEA-induced modifications of the DC maturation pathway, are significant components of the ability of DC to interpret signals inherent to SEA and Pa and induce appropriately polarized Th responses.

Calcium and Its Role in the Nuclear Translocation and Activation of Cytosolic Phospholipase A2in Cells Rendered Sensitive to TNF-Induced Apoptosis by Cycloheximide

In these experiments, we investigated the role of calcium as a second messenger in the apoptotic activation of cytosolic phospholipase A(2) (cPLA(2)). As our model, we used a murine fibroblast cell line (C3HA) that was induced to undergo apoptosis by a combination of TNF and cycloheximide. Using fura 2 Ca(2+) imaging, we found strong evidence for an intracellular calcium response after 1 h of treatment, which correlated with the onset of phosphatidylserine externalization, but preceded effector procaspase processing by several hours. The response was strongest in the perinuclear region, where mean levels rose 83% (144 +/- 14 nM in untreated cells vs 264 +/- 39 nM in treated), while cells displaying morphological evidence of apoptosis had the highest levels of calcium (250-1000 nM). Verapamil blocked this response, indicating an extracellular source for the calcium. Fluorescence microscopy revealed a pattern of nuclear translocation of cPLA(2) during apoptosis, which was also blocked by verapamil, indicating an important role for calcium in this process. In addition, we found that verapamil prevented the release of [(3)H]arachidonic acid from C3HA cells induced to undergo apoptosis by the chemotherapeutic agents vinblastine, melphalan, and cis-platinum. Together, these data suggest that calcium is important for cPLA(2) activation by diverse apoptotic stimuli.

Tumor-Infiltrating Lymphocyte Secretion of IL-6 Antagonizes Tumor-Derived TGF-β1 and Restores the Lymphokine-Activated Killing Activity

IL-6 is a multifunctional cytokine that regulates cell growth, differentiation, and cell survival. Many tumor cells produce TGF-beta1, which allows them to evade CTL-mediated immune responses. IL-6 antagonizes TGF-beta1 inhibition of CD3 cell activation. However, whether IL-6 restores NK activity, which also is suppressed by TGF-beta1, is not known. We used canine transmissible venereal tumor (CTVT), which produces TGF-beta1, as a model to determine whether IL-6 restores lymphokine-activated killer (LAK) activity. During the progression phase, CTVT cells stop expressing MHC molecules. During the regression phase, the number of surface MHC molecules increases dramatically on about one-third of tumor cells. Tumor cells that stop expressing MHC should be targeted by NK cells. In this study, we found that TGF-beta1 secreted by CTVT cells suppressed LAK cytotoxicity. Interestingly, tumor-infiltrating lymphocytes (TIL) isolated from regressing CTVT secrete high concentrations of IL-6 and antagonize the anti-LAK activity of tumor cell TGF-beta1. TIL also produce IL-6 during progression phase, but the concentration is too low to block the anti-LAK activity of TGF-beta1. There is probably a threshold concentration of IL-6 needed to reverse TGF-beta1-inhibited LAK activity. In addition, in the absence of TGF-beta1, IL-6 derived from TIL does not promote the activity of LAK. This new mechanism, in which TIL manufacture high concentrations of IL-6 to block tumor TGF-beta1 anti-LAK activity, has potential applications in cancer immunotherapy and tumor prognosis.

Chlamydia pneumoniaeMultiply in Neutrophil Granulocytes and Delay Their Spontaneous Apoptosis

The obligate intracellular bacterial pathogen Chlamydia pneumoniae (Cp) is responsible for a range of human diseases, including acute respiratory infection. Although experimental intratracheal infection with Cp results in a massive recruitment of neutrophil granulocytes (polymorphonuclear neutrophils (PMN)), the role of these cells in the defense against Cp is unclear. In this study the interactions of PMN with Cp were investigated. In vitro coincubation experiments showed that human granulocytes were able to internalize Chlamydia in an opsonin-independent manner. Importantly, phagocytosed Cp were not killed; the ingested bacteria survived and multiplied within PMN. Although uninfected granulocytes became apoptotic within 10 h, infected PMN survived up to 90 h. Coincubation with Cp significantly decreased the ratio of apoptotic PMN, as detected by morphological analysis, annexin V, and TUNEL staining. The observed antiapoptotic effect was associated with a markedly lower level of procaspase-3 processing and, consequently, reduced caspase-3 activity in infected PMN. LPS was found as a major, but not exclusive, component responsible for the observed antiapoptotic effect. Chlamydia LPS affected PMN apoptosis both by acting directly on the cells and by inducing the autocrine production of the antiapoptotic cytokine IL-8. These data show that, in contrast to other microbial pathogens that drive phagocytes into apoptosis to escape killing, Cp can extend the life span of neutrophil granulocytes, making them suitable host cells for survival and multiplication within the first hours/days after infection.

Mediation of enhanced transcription of the IL-10 gene in T cells, upon contact with human glioma cells, by Fas signaling through a protein kinase A-independent pathway

Elevated expression of IL-10 has been frequently observed in tumor tissues and tumor-infiltrating cells. We show herein that transcription of the IL-10 gene in primary peripheral T cells and T cell lines is up-regulated upon contact with glioma cells without an induction of apoptosis in those T cells. Glioma-associated IL-10 induction was suppressed by interrupting the engagement of Fas and its ligand (Fas-L) with the antagonistic Ab, ZB4, by reducing Fas-L expression of glioma cells using the Fas-L-specific ribozyme, or by preventing cell-to-cell contact in a Transwell culture setting. Cross-linking of Fas with the agonistic Ab, CH-11, triggered apoptosis and enhanced the expression of IL-10 in Jurkat cells at the transcriptional and translational levels. Inhibiting caspase activities by caspase inhibitors, Z-VAD (Z-Val-Ala-Asp(Ome)-fluoromethylketone) and Z-IETD (Z-Ile-Glu(Ome)-Thr(Ome)-Asp(Ome)-fluoromethylketone), abolished this IL-10 induction in Jurkat cells. Intracellular staining detected IL-10 proteins in Fas-cross-linked Jurkat cells and in PHA-activated T cells. However, few IL-10 proteins were detectable in Jurkat cells cocultured with glioma cells, indicating a requirement of other factors for IL-10 production. Direct activation of protein kinase A (PKA) by forskolin elevated the transcription of IL-10 in Jurkat cells. However, KT5720, a selective PKA inhibitor, reduced neither anti-Fas-triggered nor glioma-associated IL-10 expression. Phosphorylation of cAMP response element binding protein and activating transcription factor-1 in Jurkat cells was not affected by coculturing with glioma cells or by anti-Fas treatment, further suggesting a PKA-independent pathway. In summary, our results demonstrate nonlethal cross-talk between tumor and immune cells leading to IL-10 dysregulation in T cells, which might contribute to Fas-L(+) tumor-associated immunosuppression.

HSP110-HER2/neu chaperone complex vaccine induces protective immunity against spontaneous mammary tumors in HER-2/neu transgenic mice

Heat shock proteins (HSPs) are shown to be strong immunoadjuvants, eliciting both innate and adaptive immune responses against cancers. HSP110 is related in sequence to HSP70 and is approximately 4-fold more efficient in binding to and stabilizing denatured protein substrates compared with HSP70. In the present study we evaluated the ability of a heat shock complex of HSP110 with the intracellular domain (ICD) of human HER-2/neu to elicit effective antitumor immune responses and to inhibit spontaneous mammary tumors in FVB-neu (FVBN202) transgenic mice. The HSP110-ICD complex was capable of breaking tolerance against the rat neu protein and inhibiting spontaneous mammary tumor development. This vaccine induced ICD-specific IFN-gamma and IL-4 production. Depletion studies revealed that CD8(+) T cells were involved in protection against challenge with mouse mammary tumors, whereas CD4(+) T cells revealed partial protection. Increased IgG2a Ab titer in the sera of tumor-free animals after vaccination and elevated CD4(+) CD25(+) regulatory T cells in the PBL of tumor-bearing animals suggested that IFN-gamma-producing Th1 cells may be responsible for partial protection of CD4(+) T cells against the mammary tumor challenge, whereas CD4(+)CD25(+) regulatory T cells (Th2 cells) may suppress the antitumor immune responses. Together, these results suggest that HSP110-ICD complex can elicit effective IFN-gamma-producing T cells against spontaneous mammary tumors and that up-regulation of CD4(+) CD25(+) regulatory T cells may prevent complete eradication of the tumor following immunotherapy.