Unstimulated human CD4 lymphocytes express a cytoplasmic immature form of the common cytokine receptor gamma-chain

As a component of various cytokine receptors, common cytokine receptor gamma-chain (gamma(c)) is essential in the development of the immune system and plays an important role in different stages of inflammatory and immune responses. Here we establish that resting CD4 T cells and the Jurkat CD4 T cell line do not express the mature form of gamma(c) (64 kDa) recognized by mAb Tugh4. However, these cells constitutively transcribe the corresponding gamma(c) gene. This apparent paradox was solved by the demonstration that polyclonal anti-gamma(c) Abs detected endoglycosidase-H-sensitive immature forms of gamma(c) (54-58 kDa) expressed by quiescent CD4 T lymphocytes and Jurkat cells. Immature gamma(c) is characterized as an intracellular component localized in the endoplasmic reticulum. Pulse-chase analysis shows that the immature gamma(c) is rapidly degraded after synthesis. After activation of CD4 T lymphocytes, and as seen in the CD4 T cell line Kit 225, the endoglycosidase-H-resistant mature form of gamma(c) is detectable at the cell surface and in the endosomal compartment. For the first time, our results demonstrate that a cytokine receptor chain may be constitutively produced as an immature form. Furthermore, this supports the notion that expression of the functional form of gamma(c) may require intracellular interactions with lineage- or subset-specific molecular partners.

Down-regulation of IL-12 p40 gene in Plasmodium berghei-infected mice

We analyzed the mechanism that causes suppression of IL-12 p40 gene induction during Plasmodium berghei infection. Although IL-12 together with IFN-gamma plays an important role in protection against pathogenic infection, the IL-12 p70 protein production of infected macrophages is lower than that by the uninfected macrophages. We showed in the present study that the induction of IL-12 p40 gene but not IL-12 p35 gene in macrophages of P. berghei-infected mice was profoundly inhibited. The inhibition was induced by interaction with macrophages that had contacted with P. berghei-infected erythrocytes and was mediated by a soluble factor, IL-10. There was comparable activation of NF-kappaB in uninfected and infected cells. The induction of IFN-regulatory factor-1 gene was comparable in transcription level in uninfected and infected cells, while the unidentified complex formation of IFN-regulatory factor-1 was observed in infected cells. Therefore, the inhibition of the IL-12 p40 gene induction appeared to be regulated at transcriptional regulation level of the gene.

TAP-independent presentation of CTL epitopes by Trojan antigens

The majority of CTL epitopes are derived from intracellular proteins that are degraded in the cytoplasm by proteasomes into peptides that are transported into the endoplasmic reticulum by the TAP complex. These peptides can be further processed into the optimal size (8-10 residues) for binding with nascent MHC class I molecules, generating complexes that are exported to the cell surface. Proteins or peptides containing CTL epitopes can be introduced into the cytoplasm of APCs by linking them to membrane-translocating Trojan carriers allowing their incorporation into the MHC class I Ag-processing pathway. The present findings suggest that these "Trojan" Ags can be transported into the endoplasmic reticulum in a TAP-independent way where they are processed and trimmed into CTL epitopes. Furthermore, processing of Trojan Ags can also occur in the trans-Golgi compartment, with the participation of the endopeptidase furin and possibly with the additional participation of a carboxypeptidase. We believe that these findings will be of value for the design of CTL-inducing vaccines for the treatment or prevention of infectious and malignant diseases.

Cutting edge: IL-18-transgenic mice: in vivo evidence of a broad role for IL-18 in modulating immune function

IL-18 has been shown to be a strong cofactor for Th1 T cell development. However, we previously demonstrated that when IL-18 was combined with IL-2, there was a synergistic induction of a Th2 cytokine, IL-13, in both T and NK cells. More recently, we and other groups have reported that IL-18 can potentially induce IgE, IgG1, and Th2 cytokine production in murine experimental models. Here, we report on the generation of IL-18-transgenic (Tg) mice in which mature mouse IL-18 cDNA was expressed. CD8+CD44high T cells and macrophages were increased, but B cells were decreased in these mice while serum IgE, IgG1, IL-4, and IFN-gamma levels were significantly increased. Splenic T cells in IL-18 Tg mice produced higher levels of IFN-gamma, IL-4, IL-5, and IL-13 than control wild-type mice. Thus, aberrant expression of IL-18 in vivo results in the increased production of both Th1 and Th2 cytokines.

TNF-α Controls Intracellular Mycobacterial Growth by Both Inducible Nitric Oxide Synthase-Dependent and Inducible Nitric Oxide Synthase-Independent Pathways

The role of TNF-alpha in the control of mycobacterial growth in murine macrophages was studied in vitro. Infection of macrophages from TNF-alpha gene disrupted (TNF-knockout (KO)) mice with recombinant Mycobacterium bovis bacillus Calmette Guérin (BCG) expressing the vector only (BCG-vector) resulted in logarithmic growth of the intracellular bacilli. Infection with BCG-secreting murine TNF-alpha (BCG-TNF) led to bacillary killing. Killing of BCG-TNF was associated with rapid accumulation of inducible NO synthase (iNOS) protein and the production of nitrite. The uncontrolled growth of BCG-vector was associated with low iNOS expression but no nitrite production. Thus, iNOS expression appears to be TNF-alpha independent but iNOS generation of NO requires TNF-alpha. In cultures of TNF-KO macrophages infected with BCG-TNF, inhibition of iNOS by aminoguanidine (AMG) abolished the killing of the bacilli. However, the growth of the organisms was still inhibited, suggesting an iNOS-independent TNF-alpha-mediated growth inhibition. To confirm this, macrophages from iNOS-KO mice were infected with either BCG-vector or BCG-TNF. As expected, no nitrite was detected in the culture medium. TNF-alpha was detected only when the cells were infected with BCG-TNF. In the iNOS-KO macrophages, the growth of BCG was inhibited only in the BCG-TNF infection. These results suggest that in the absence of iNOS activity, TNF-alpha stimulates macrophages to control the growth of intracellular BCG. Thus, there appears to be both a TNF-alpha-dependent-iNOS-dependent killing pathway as well as a TNF-alpha-dependent-iNOS-independent growth inhibitory pathway for the control of intracellular mycobacteria in murine macrophages.

Regulation of mast cell survival by IgE

Mast cells play critical roles in hypersensitivity and in defense against certain parasites. We provide evidence that mouse mast cell survival and growth are promoted by monomeric IgE binding to its high-affinity receptor, Fc epsilon RI. Monomeric IgE does not promote DNA synthesis but suppresses the apoptosis induced by growth factor deprivation. This antiapoptotic effect occurs in parallel with IgE-induced increases in Fc epsilon RI surface expression but requires the continuous presence of IgE. This process does not involve the FasL/Fas death pathway or several Bcl-2 family proteins and induces a distinctly different signal than Fc epsilon RI cross-linking. The ability of IgE to enhance mast cell survival and Fc epsilon RI expression may contribute to amplified allergic reactions.

Immunostimulation of rat primary astrocytes decreases intracellular ATP level

In this study we investigated the effect of immunostimulation on intracellular ATP level in rat glial cells. Rat primary astrocytes or C6 glioma cells were treated for 48 h with IFN-gamma, LPS or IFN-gamma plus LPS. These treatments increased NO production from the cells and a synergistic increase in NO production was observed with IFN-gamma plus LPS. Intracellular ATP level was decreased to about half the control level at the highest concentration of IFN-gamma (100 U/ml) plus LPS (1 microg/ml) without affecting cell viability. The level of intracellular ATP was inversely correlated with the extent of NO production from the glial cells. The increase in NO production is at least 6 h ahead of the initiation of ATP depletion, and NOS inhibitor N(G)-nitro-L-arginine (NNA) or Nomega-nitro-L-arginine methyl ester (L-NAME) inhibited NO production and ATP depletion. Exogenous addition of peroxynitrite generator 3-morpholinosydnonimine (SIN-1) and to a lesser extent NO generator S-nitroso-N-acetylpenicillamine (SNAP) depleted intracellular ATP level in a dose-dependent manner. The results from the present study imply that immunostimulation of rat glial cells decreases the intracellular ATP level without affecting cell viability. Considering the role of astrocytes as an essential regulator of the extracellular environment in the brain, the immunostimulation-induced decrease in intracellular ATP level may participate in the pathogenesis of various neurological diseases.

T Cells Enhance Production of IL-18 by Monocytes in Response to an Intracellular Pathogen

We studied the effect of T cells on IL-18 production by human monocytes in response to Mycobacterium tuberculosis. Addition of activated T cells markedly enhanced IL-18 production by monocytes exposed to M. tuberculosis. This effect was mediated by a soluble factor and did not require cell-to-cell contact. The effect of activated T cells was mimicked by recombinant IFN-gamma and was abrogated by neutralizing Abs to IFN-gamma. IFN-gamma also enhanced the capacity of alveolar macrophages to produce IL-18 in response to M. tuberculosis, suggesting that this mechanism also operates in the lung during mycobacterial infection. IFN-gamma increased IL-18 production by increasing cleavage of pro-IL-18 to mature IL-18, as it enhanced caspase-1 activity but did not increase IL-18 mRNA expression. These findings suggest that activated T cells can contribute to the initial immune response by augmenting IL-18 production by monocytes in response to an intracellular pathogen.

Transcriptional regulation of intracellular IL-1 receptor antagonist gene by IL-1 alpha in primary mouse keratinocytes

The inflammatory cytokine IL-1alpha mediates inflammatory reactions in skin and up-regulates the expression of other proinflammatory genes. We previously found that IL-1alpha also increases steady state mRNA levels for intracellular IL-1 receptor antagonist (icIL-1Ra) in primary mouse keratinocytes; however, the mechanism for this was unknown. Here we show that increased expression in primary keratinocytes is due to increased rates of transcription. To study the transcriptional regulation of icIL-1Ra expression induced by IL-1alpha, we functionally characterized 4.5 kb of the 5'-flanking region of the human icIL-1Ra gene. Deletion analysis showed that regulatory elements were contained in the -598- and -288-bp region upstream of the transcription start site. Then we investigated cis- and trans-acting factors required for icIL-1Ra expression and found that a NF-IL-6 site and a NF-kappaB site in the icIL-1Ra promoter were responsible for IL-1alpha-induced icIL-1Ra expression. Moreover, gel shift assays and cotransfection experiments showed that CCAAT/enhancer-binding proteins alpha, beta, and p65 bind to the NF-IL-6 site and NF-kappaB site, respectively, and functionally trans-activate the icIL-1Ra promoter. Finally, mutational analysis confirmed that these elements were both essential for maximal transcription induced by IL-1alpha.

CD45 tyrosine phosphatase controls common gamma-chain cytokine-mediated STAT and extracellular signal-related kinase phosphorylation in activated human lymphoblasts: inhibition of proliferation without induction of apoptosis

The objective of this study was to test whether CD45 signals can influence signaling processes in activated human lymphoblasts. To this end, we generated lymphoblasts which proliferate in response to common gamma-chain cytokines, but readily undergo apoptosis after cytokine withdrawal. In experiments with the CD45R0 mAb UCHL-1, but not control CD45 mAbs, we found significant inhibition of proliferation. Interestingly, the pan-CD45 mAb GAP8.3, which is most effective in inhibition of OKT-3-mediated proliferation in quiescent lymphocytes, was ineffective in lymphoblasts. Addition of CD3 mAb OKT-3 had no influence on IL-2-mediated proliferation (with or without UCHL-1). In contrast, after addition of OKT-3 to IL-4- and IL-7-stimulated proliferation assays, UCHL-1 signals could not significantly alter cellular proliferation. We did not find induction of apoptosis following CD45R0 signaling. In Western blots using mAbs detecting phosphorylated STAT-3, STAT-5, STAT-6, or extracellular signal-related kinase 1/2, we found that CD45R0 signaling could effectively diminish phosphorylation of these intracellular signaling components. Using RT-PCR, we found that CD45R0 signaling inhibited IL-2 mRNA production without major influence on IL-13, IL-5, or IFN-gamma mRNA levels. Costimulation with OKT-3 and IL-2 optimally induced secretion of IFN-gamma, TNF-alpha, and IL-5, which was not decreased by CD45 signals. In conclusion, we illustrate that CD45R0 signals control early cytokine receptor-associated signaling processes and mRNA and DNA synthesis in activated human lymphoblasts. Furthermore, we show the existence of CD45 epitopes (GAP8.3), which are active and critical for signaling in quiescent lymphocytes, but are nonfunctional in activated human lymphoblasts.

Increasing the affinity for tumor antigen enhances bispecific antibody cytotoxicity

We tested the hypothesis that bispecific Abs (Bsab) with increased binding affinity for tumor Ags augment retargeted antitumor cytotoxicity. We report that an increase in the affinity of Bsab for the HER2/neu Ag correlates with an increase in the ability of the Bsab to promote retargeted cytotoxicity against HER2/neu-positive cell lines. A series of anti-HER2/neu extracellular domain-directed single-chain Fv fragments (scFv), ranging in affinity for HER2/neu from 10(-7) to 10(-11) M, were fused to the phage display-derived NM3E2 human scFV: NM3E2 associates with the extracellular domain of human FcgammaRIII (CD16). The resulting series of Bsab promoted cytotoxicity of SKOV3 human ovarian carcinoma cells overexpressing HER2/neu by human PBMC preparations containing CD16-positive NK cells. The affinity for HER2/neu clearly influenced the ability of the Bsab to promote cytotoxicity of (51)Cr-labeled SKOV3 cells. Lysis was 6.5% with an anti-HER2/neu K(D) = 1.7 x 10(-7) M, 14.5% with K(D) = 5.7 x 10(-9) M, and 21.3% with K(D) = 1.7 x 10(-10) M at 50:1 E:T ratios. These scFv-based Bsab did not cross-link receptors and induce leukocyte calcium mobilization in the absence of tumor cell engagement. Thus, these novel Bsab structures should not induce the dose-limiting cytokine release syndromes that have been observed in clinical trials with intact IgG BSAB: Additional manipulations in Bsab structure that improve selective tumor retention or facilitate the ability of Bsab to selectively cross-link tumor and effector cells at tumor sites should further improve the utility of this therapeutic strategy.

CD24 induces apoptosis in human B cells via the glycolipid-enriched membrane domains/rafts-mediated signaling system

The glycosylphosphatidylinositol-anchored CD24 protein is a B cell differentiation Ag that is expressed on mature resting B cells but disappears upon Ag stimulation. We used Burkitt's lymphoma (BL) cells, which are thought to be related to germinal center B cells, to examine the biological effect of Ab-mediated CD24 cross-linking on human B cells and observed 1) induction of apoptosis in BL cells mediated by cross-linking of CD24; and 2) synergism between the cross-linking of CD24 and that of the B cell receptor for Ag in the effect on apoptosis induction. We also observed activation of mitogen-activated protein kinases following CD24 cross-linking, suggesting that CD24 mediates the intracellular signaling that leads to apoptosis in BL cells. Although CD24 has no cytoplasmic portion to transduce signals intracellularly, analysis of biochemically separated glycolipid-enriched membrane (GEM) fractions indicated enhanced association of CD24 and Lyn protein tyrosine kinase in GEM as well as increased Lyn kinase activity after CD24 cross-linking, suggesting that CD24 mediates intracellular signaling via a GEM-dependent mechanism. Specific microscopic cocapping of CD24 and Lyn, but not of other kinases, following CD24 cross-linking supported this idea. We further observed that apoptosis induction by cross-linking is a common feature shared by GEM-associated molecules expressed on BL cells, including GPI-anchored proteins and glycosphingolipids. CD24-mediated apoptosis in BL cells may provide a model for the cell death mechanism initiated by GEM-associated molecules, which is closely related to B cell receptor for Ag-mediated apoptosis.

Flow cytometric determination of intracellular or secreted IFNgamma for the quantification of antigen reactive T cells

The detection of antigen-induced IFNgamma secretion at the single cell level can be used to identify and enumerate antigen-reactive T cells from peripheral blood. This study was performed to analyze the suitability of T cell enumeration by flow cytometry in comparison with the ELISPOT assay. Peripheral blood mononuclear cell (PBMC) samples from six HLA-A2+ healthy subjects were analysed for the frequency of influenza-reactive CD8+ T cells by flow cytometry detecting either intracellular IFNgamma (IC-FC) or secreted IFNgamma (S-FC). All samples were also analysed by IFNgamma ELISPOT assay. The frequency of influenza peptide-reactive T cells determined by IC-FC was 0.01 to 0.34% of CD8+ T cells and by ELISPOT assay 0.02 to 0.23% of CD8+ T cells (n=6 subjects) with a high inter-assay reproducibility and a close correlation between the assays (r=0.77, P<0.001). Little or no IFNgamma production was observed in unstimulated PBMC samples using either the IC-FC or the ELISPOT assay. In contrast, using S-FC large numbers of IFNgamma-secreting CD8+ T cells (0.37% to 5.55%, n=6 subjects) were detected in unstimulated PBMC. The frequency of influenza-reactive CD8+ T cells (0.57-5.19%, n=6 subjects) determined by S-FC did not correlate with the values from the IC-FC or ELISPOT assays. This comparative study shows the suitability of the determination of frequencies of antigen reactive T cells in PBMC by IC-FC. The advantage of IC-FC is the possibility to phenotype simultaneously antigen-reactive T cells.

IFN-alpha and IL-10 induce the differentiation of human type 1 T regulatory cells

CD4(+) T regulatory type 1 (Tr1) cells suppress Ag-specific immune responses in vitro and in vivo. Although IL-10 is critical for the differentiation of Tr1 cells, the effects of other cytokines on differentiation of naive T cells into Tr1 cells have not been investigated. Here we demonstrate that endogenous or exogenous IL-10 in combination with IFN-alpha, but not TGF-beta, induces naive CD4(+) T cells derived from cord blood to differentiate into Tr1 cells: IL-10(+)IFN-gamma(+)IL-2(-/low)IL-4(-). Naive CD4(+) T cells derived from peripheral blood require both exogenous IL-10 and IFN-alpha for Tr1 cell differentiation. The proliferative responses of the Tr1-containing lymphocyte populations, following activation with anti-CD3 and anti-CD28 mAbs, were reduced. Similarly, cultures containing Tr1 cells displayed reduced responses to alloantigens via a mechanism that was partially mediated by IL-10 and TGF-beta. More importantly, Tr1-containing populations strongly suppressed responses of naive T cells to alloantigens. Collectively, these results show that IFN-alpha strongly enhances IL-10-induced differentiation of functional Tr1 cells, which represents a first major step in establishing specific culture conditions to generate T regulatory cells for biological and biochemical analysis, and for cellular therapy to induce peripheral tolerance in humans.

Intracellular Antibody Neutralizes Listeria Growth

We previously reported that treatment of mice with a neutralizing mAb against listeriolysin O (LLO), the pore-forming toxin of Listeria monocytogenes, provided resistance to this intracellular bacterium. We evaluated whether anti-LLO mAb would affect Listeria handling by macrophages, essential cells in Listeria resistance. Macrophages infected in the presence of anti-LLO mAb showed a marked reduction in intracellular Listeria growth, with a concomitant block in LLO-dependent Listeria passage from phagosome to cytosol. Anti-LLO mAb did not opsonize Listeria but, rather, acted within macrophages to neutralize LLO. Importantly, anti-LLO mAb effects on Listeria growth were independent of Fcgamma receptor expression, IFNgamma signaling, and production of nitric oxide and superoxide. These results identify a novel mechanism for antibody control of bacteria within macrophages.

Coregulation of CXC chemokine receptor and CD4 expression on T lymphocytes during allogeneic activation

Upon activation, naive T cells alter their migratory patterns, acquiring the ability to move through peripheral tissues as well as the general lymphoid circulation. Although the mechanisms responsible for these alterations are not well understood, changes in chemokine receptor expression may play a critical role. To investigate these changes, the expression patterns of two chemokine receptors, CXCR3 and CXCR4, were compared on CD4(+) T cells following activation in the MLR. By day 9 of activation, expression of the inflammatory chemokine receptor CXCR3 was up-regulated, while expression of the homeostatic chemokine receptor CXCR4 was down-regulated. Alterations in receptor expression occurred almost exclusively on a subpopulation of T cells that expressed higher levels of CD4. These CD4(high) T cells demonstrated many characteristics of activated T cells and had undergone division in the MLR. By day 9 of culture, the majority of CXCR3(+) and CXCR4(-) cells had divided and had acquired an activated/memory phenotype (CD45RA(-) CD45RO(+) CD69(+) CD25(+)). The levels of transcripts for both CXCR3 and CXCR4 were increased upon allo-activation. The discrepancy between levels of CXCR4 mRNA and surface protein was not due to sequestration of the receptor in intracellular compartments, as CXCR4 was not detectable intracellularly. However, intracellular CXCR3 was readily detectable. Finally, cells from allogeneic cultures demonstrated enhanced migration toward IFN-inducible T cell alpha chemoattractant and reduced migration toward stromal cell-derived factor-1 compared with syngeneic controls, thus suggesting that the observed switch in receptor expression may at least partly contribute to the differential patterns of migration displayed by naive and memory T cells.

CD40 signaling converts a minimally immunogenic antigen into a potent vaccine against the intracellular pathogen Listeria monocytogenes

Conventional vaccination strategies have failed for numerous pathogens, and the development of novel approaches to vaccine development is a major public health priority. Killed or subunit vaccines represent an attractive approach due to their safety, but they suffer from low immunogenicity and generally require adjuvants. In this study, the possibility of harnessing CD40 signaling for enhancing the immunogenicity of killed vaccines was investigated. Intravenous immunization of C57BL/6 mice with heat-killed Listeria monocytogenes (HKL) induced minimal immunity, but HKL administered together with an agonistic anti-CD40 mAb induced high levels of both CD4(+) and CD8(+) T cells capable of producing IFN-gamma following in vitro HKL stimulation. HKL/anti-CD40 vaccination elicited robust protection against subsequent Listeria challenge. Approximately 1000-fold fewer bacteria were detected in the liver and spleen of vaccinated mice, and vaccinated mice were also able to resist a normally lethal Listeria challenge. CD40-mediated adjuvant activity required endogenous IL-12 at the time of vaccination, and protection was mediated by both CD8(+) and CD4(+) T cells. Thus, CD40 signaling can deliver potent adjuvant activity for vaccination against intracellular pathogens and is particularly effective for pathogens requiring both CD4(+) and CD8(+) T cells for effective control.

Intracellular pool of IL-10 receptors in specific granules of human neutrophils: differential mobilization by proinflammatory mediators

IL-10 has a wide range of effects tending to control inflammatory responses. We used flow cytometry to study IL-10 binding at the polymorphonuclear neutrophil (PMN) surface and its modulation by various proinflammatory agents. Little IL-10 bound to the surface of resting PMN. However, binding was strongly increased after stimulation with LPS and proinflammatory cytokines such as TNF and GM-CSF. IL-1 and IL-8 did not significantly modify IL-10 binding. Cycloheximide had no effect on TNF-induced IL-10 binding, strongly suggesting the release of a pre-existing pool of IL-10R rather than de novo receptor synthesis by PMN. This was confirmed by the inhibitory effect of pentoxifylline, an inhibitor of degranulation. The existence of an intracellular pool of IL-10R was shown by flow cytometry, immunocytochemical staining, and Western blotting with several anti-human IL-10R Abs. In subcellular fractions of resting PMN, IL-10R was mainly located in the specific granule fraction, and was absent from azurophil granules and cytosol. We also tested the mobilization of specific granules by measuring the release of lactoferrin, their reference marker. The differential effects of the proinflammatory agents on IL-10 binding matched their effects on lactoferrin release and may therefore be related to differential mobilization of specific granules by these agents. Furthermore, the kinetics of TNF-induced up-regulation of IL-10 binding to PMN ran parallel to the kinetics of the inhibitory effect of IL-10 on the oxidative burst, suggesting a key role of IL-10R mobilization from specific granules to the membranes in optimal regulation of inflammatory responses.

Toll-like receptor 4 mediates intracellular signaling without TNF-alpha release in response to Cryptococcus neoformans polysaccharide capsule

Toll-like receptors (TLR) 2 and 4 are cell surface receptors that in association with CD14 enable phagocytic inflammatory responses to a variety of microbial products. Activation via these receptors triggers signaling cascades, resulting in nuclear translocation of NF-kappa B and a proinflammatory response including TNF-alpha production. We investigated whether TLRs participate in the host response to Cryptococcus neoformans glucuronoxylomannan (GXM), the major capsular polysaccharide of this fungus. Chinese hamster ovary fibroblasts transfected with human TLR2, TLR4, and/or CD14 bound fluorescently labeled GXM. The transfected Chinese hamster ovary cells were challenged with GXM, and activation of an NF-kappa B-dependent reporter construct was evaluated. Activation was observed in cells transfected with both CD14 and TLR4. GXM also stimulated nuclear NF-kappa B translocation in PBMC and RAW 264.7 cells. However, stimulation of these cells with GXM resulted in neither TNF-alpha secretion nor activation of the extracellular signal-regulated kinase 1/2, p38, and stress-activated protein kinase/c-Jun N-terminal kinase mitogen-activated protein kinase pathways. These findings suggest that TLRs, in conjunction with CD14, function as pattern recognition receptors for GXM. Furthermore, whereas GXM stimulates cells to translocate NF-kappa B to the nucleus, it does not induce activation of mitogen-activated protein kinase pathways or release of TNF-alpha. Taken together, these observations suggest a novel scenario whereby GXM stimulates cells via CD14 and TLR4, resulting in an incomplete activation of pathways necessary for TNF-alpha production.

Regulatory activity of autocrine IL-10 on dendritic cell functions

IL-10 is a critical cytokine that blocks the maturation of dendritic cells (DCs), but the relevance of autocrine IL-10 on DC functions has not been investigated. In this study, we found that immature monocyte-derived DCs released low but sizeable amounts of IL-10. After stimulation with bacteria, LPS, lipoteichoic acid, or soluble CD40 ligand, DCs secreted high levels of IL-10. Addition of an anti-IL-10-neutralizing Ab to immature DCs as well as to soluble CD40 ligand- or LPS-maturing DCs led to enhanced expression of surface CD83, CD80, CD86, and MHC molecules and markedly augmented release of TNF-alpha and IL-12, but diminished IL-10 mRNA expression. Moreover, DCs treated with anti-IL-10 Ab showed an increased capacity to activate allogeneic T cells and primed naive T cells to a more prominent Th1 polarization. DC maturation and IL-10 neutralization were associated with enhanced accumulation of the IL-10 receptor binding chain (IL-10R1) mRNA and intracellular IL-10R1 protein. In contrast, surface IL-10R1 and IL-10 binding activity diminished in mature DCs. These results indicate that autocrine IL-10 prevents spontaneous maturation of DCs in vitro, limits LPS- and CD40-mediated maturation, and increases IL-10 production by DCs. Moreover, IL-10R expression appears to be regulated by both transcriptional and posttranscriptional mechanisms. Endogenous IL-10 and IL-10R can be relevant targets for the manipulation of DC functions.

Intracellular signaling by the killer immunoglobulin-like receptors and Ly49

Once thought to be promiscuous killers, it is now known that natural killer (NK) cells possess an elaborate array of receptors that regulate NK cytotoxic and secretory functions upon interaction with target cell MHC class I proteins. These receptors, known as killer cell immunoglobulin-like receptors (KIRs) in humans, and Ly49 receptors in the mouse, have become the focus of intense study in an effort to discern the underlying biology of these large receptor families. These receptor families include both inhibitory and activating receptors. Interrogation of a target expressing KIR ligands leads to coengagement of the inhibitory receptor with as-yet poorly defined activation receptors. Kinases activated during engagement mediate the phosphorylation of the KIR or Ly49 cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). The phosphorylated ITIMs serve as efficient recruitment points for the cytosolic protein tyrosine phosphatases, SHP-1 and SHP-2, resulting in the dephosphorylation of substrates critical for cellular activation. In contrast, some KIRs and Ly49s lack the ITIM and possess a charged residue in their transmembrane domains that mediates interaction with the DAP12 signal transduction chain. DAP12 uses its cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM) to mediate cellular activation. Engagement of a DAP12 coupled KIR or Ly49 results in phosphorylation of DAP12, and other key substrates, including the Syk tryosine kinase, phospholipase C, and c-Cbl. DAP12 activation then leads to the Mapk cascade and ultimately to enhanced degranulation, and production of cytokines and chemokines. Although the context in which inhibitory and activating KIR and Ly49s function is not yet known, the dissection of the activating and inhibitory signal transduction pathways should shed light on their method of integration into the activation sequela of NK cells. Ultimately, this work will lead to concrete understanding of the immunobiology of these seemingly antagonistic receptor systems.

Neuronal expression of a functional receptor for the C5a complement activation fragment

The present studies were undertaken to determine whether neuronal subsets in normal brains constitutively express functionally competent C5a receptors. In situ hybridization studies coupled with immunohistochemical approaches revealed that most neurons in the hippocampal formation, many pyramidal cortical neurons, and cerebellar Purkinje neurons in normal human and murine brains constitutively express C5a receptors. Neuronal C5a receptors bound C5a-coated fluorescent microspheres, and primary rodent hippocampal neurons responded to C5a with increased calcium fluxes via a pertussis-sensitive, presumably Gi-coupled protein. Additional studies with human neuroblastoma cells conducted to address the functional role of C5a receptors revealed that C5a triggered rapid activation of protein kinase C and activation and nuclear translocation of the NF-kappa B transcription factor. In addition, C5a was found to be mitogenic for undifferentiated human neuroblastoma cells, a novel action for the C5aR. In contrast, C5a protected terminally differentiated human neuroblastoma cells from toxicity mediated by the amyloid A beta peptide. Thus, normal rodent hippocampal neurons as well as undifferentiated and differentiated human neuroblastoma cells express functional C5a receptors. These results have implications for understanding the role of neuronal C5aR receptors in normal neuronal development, neuronal homeostasis, and neuroinflammatory conditions such as Alzheimer's disease.

Dendritic cells acquire antigens from live cells for cross-presentation to CTL

Dendritic cells (DC) can readily capture Ag from dead and dying cells for presentation to MHC class I-restricted CTL. We now show by using a primate model that DC also acquire Ag from healthy cells, including other DC. Coculture assays showed that fluorescently labeled plasma membrane was rapidly and efficiently transferred between DC, and transfer of intracellular proteins was observed to a lesser extent. Acquisition of labeled plasma membrane and intracellular protein was cell contact-dependent and was primarily a function of immature DC, whereas both immature and CD40L-matured DC could serve as donors. Moreover, immature DC could acquire labeled plasma membrane and intracellular proteins from a wide range of hemopoietic cells, including macrophages, B cells, and activated T cells. Notably, macrophages, which readily phagocytose apoptotic bodies, were very inefficient at acquiring labeled plasma membrane and intracellular proteins from other live macrophages or DC. With live-cell imaging techniques, we demonstrate that individual DC physically extract plasma membrane from other DC, generating endocytic vesicles of up to 1 microm in diameter. Finally, DC but not macrophages acquired an endogenous melanoma Ag expressed by live DC and cross-presented Ag to MHC class I-restricted CTL, demonstrating the immunological relevance of our finding. These data show for the first time that DC readily acquire Ag from other live cells. We suggest that Ag acquisition from live cells may provide a novel mechanism whereby DC can present Ag in the absence of direct infection, and may serve to expand and regulate the immune response in vivo.

Mice lacking the multidrug resistance protein 1 are resistant to Streptococcus pneumoniae-induced pneumonia

Leukotrienes (LTs) are considered important for antibacterial defense in the lung. Multidrug resistance protein 1 (mrp1) is a transmembrane protein responsible for the cellular extrusion of LTC(4). To determine the role of mrp1 in host defense against pneumonia, mrp1(-/-) and wild-type mice were intranasally inoculated with Streptococcus pneumoniae. mrp1(-/-) mice displayed a diminished outgrowth of pneumococci in lungs and a strongly reduced mortality. These findings were related to an effect of mrp1 on LT metabolism, because survival was similar in mrp1(-/-) and wild-type mice treated with the 5-lipoxygenase-activating protein inhibitor MK-886. Although LTC(4) levels remained low in the bronchoalveolar lavage fluid of mrp1(-/-) mice, LTB(4) concentrations were higher than in wild-type mice. These elevated LTB(4) concentrations were important for the relative protection of mrp1(-/-) mice, because the LTB(4) antagonist LTB(4)-dimethyl amide abolished their survival advantage. In vitro experiments suggested that the intracellullar accumulation of LTC(4) in mrp1(-/-) mice results in product inhibition of LTC(4)-synthase, diminishing substrate competition between LTA(4)-hydrolase (which yields LTB(4)) and LTC(4)-synthase for the available LTA(4). We conclude that mrp1(-/-) mice are resistant against pneumococcal pneumonia by a mechanism that involves increased release of LTB(4). These results identify mrp1 as a novel target for adjunctive therapy in pneumonia.

CXC chemokine receptor 4 expression and function in human astroglioma cells

Chemokines constitute a superfamily of proteins that function as chemoattractants and activators of leukocytes. Astrocytes, the major glial cell type in the CNS, are a source of chemokines within the diseased brain. Specifically, we have shown that primary human astrocytes and human astroglioma cell lines produce the CXC chemokines IFN-gamma-inducible protein-10 and IL-8 and the CC chemokines monocyte chemoattractant protein-1 and RANTES in response to stimuli such as TNF-alpha, IL-1beta, and IFN-gamma. In this study, we investigated chemokine receptor expression and function on human astroglioma cells. Enhancement of CXC chemokine receptor 4 (CXCR4) mRNA expression was observed upon treatment with the cytokines TNF-alpha and IL-1beta. The peak of CXCR4 expression in response to TNF-alpha and IL-1beta was 8 and 4 h, respectively. CXCR4 protein expression was also enhanced upon treatment with TNF-alpha and IL-1beta (2- to 3-fold). To study the functional relevance of CXCR4 expression, stable astroglioma transfectants expressing high levels of CXCR4 were generated. Stimulation of cells with the ligand for CXCR4, stromal cell-derived factor-1alpha (SDF-1alpha), resulted in an elevation in intracellular Ca(2+) concentration and activation of the mitogen-activated protein kinase cascade, specifically, extracellular signal-regulated kinase 2 (ERK2) mitogen-activated protein kinase. Of most interest, SDF-1alpha treatment induced expression of the chemokines monocyte chemoattractant protein-1, IL-8, and IFN-gamma-inducible protein-10. SDF-1alpha-induced chemokine expression was abrogated upon inclusion of U0126, a pharmacological inhibitor of ERK1/2, indicating that the ERK signaling cascade is involved in this response. Collectively, these data suggest that CXCR4-mediated signaling pathways in astroglioma cells may be another mechanism for these cells to express chemokines involved in angiogenesis and inflammation.