Mast Cell Sarcoma Mimicking Lymphoma or Metastatic Disease on 18 F-FDG PET/CT

ABSTRACT

We report an 18 F-FDG PET/CT scan of a 47-year-old man diagnosed with diffuse mast cell sarcoma with lymph node, bone, liver, spleen, and lung involvement. This interesting image should remind colleagues to consider mast cell sarcoma as a rare differential diagnosis in patients with multiple, intensely hypermetabolic lesions in various organs and lymph nodes.

CD3 delta establishes a functional link between the T cell receptor and CD8

T cells expressing T cell receptor (TCR) complexes that lack CD3 delta, either due to deletion of the CD3 delta gene, or by replacement of the connecting peptide of the TCR alpha chain, exhibit severely impaired positive selection and TCR-mediated activation of CD8 single-positive T cells. Because the same defects have been observed in mice expressing no CD8 beta or tailless CD8 beta, we examined whether CD3 delta serves to couple TCR.CD3 with CD8. To this end we used T cell hybridomas and transgenic mice expressing the T1 TCR, which recognizes a photoreactive derivative of the PbCS 252-260 peptide in the context of H-2K(d). We report that, in thymocytes and hybridomas expressing the T1 TCR.CD3 complex, CD8 alpha beta associates with the TCR. This association was not observed on T1 hybridomas expressing only CD8 alpha alpha or a CD3 delta(-) variant of the T1 TCR. CD3 delta was selectively co-immunoprecipitated with anti-CD8 antibodies, indicating an avid association of CD8 with CD3 delta. Because CD8 alpha beta is a raft constituent, due to this association a fraction of TCR.CD3 is raft-associated. Cross-linking of these TCR-CD8 adducts results in extensive TCR aggregate formation and intracellular calcium mobilization. Thus, CD3 delta couples TCR.CD3 with raft-associated CD8, which is required for effective activation and positive selection of CD8(+) T cells.

Szygium aromaticum (L.) Merr. Et Perry (Myrtaceae) flower bud induces apoptosis of p815 mastocytoma cell line

This study was conducted to investigate SAFB-induced apoptosis of mast cells as it pertains to both its basic drug mechanism and the potential therapeutics of the pathologic conditions accompanying mast cell proliferation. SAFB induced many apoptotic manifestations as evidenced by changes in cell morphology, generation of DNA fragmentation, activation of caspase 3, and DNA hypoploidy. The reduction of mitochondrial membrane potential and the release of cytochrome c to cytosol were also demonstrated. However, reduction of mitochondrial membrane potential and cytochrome c release were not prevented by caspase inhibitor zVAD-fmk or PTP blockers such as bongkrekic acid and cyclosporin A. Expression levels of Bcl-2 and Fas remained unchanged following SAFB treatment. This results suggest that the clinical effect of SAFB may depend on the pharmacological mechanism regulating the demise of mast cells.

Cloning, Golgi localization, and enzyme activity of the full-length heparin/heparan sulfate-glucuronic acid C5-epimerase

While studying the cellular localization and activity of enzymes involved in heparan sulfate biosynthesis, we discovered that the published sequence for the glucuronic acid C5-epimerase responsible for the interconversion of d-glucuronic acid and l-iduronic acid residues encodes a truncated protein. Genome analysis and 5'-rapid amplification of cDNA ends was used to clone the full-length cDNA from a mouse mastocytoma cell line. The extended cDNA encodes for an additional 174 amino acids at the amino terminus of the protein. The murine sequence is 95% identical to the human epimerase identified from genomic sequences and fits with the general size and structure of the gene from Drosophila melanogaster and Caenorhabditis elegans. Full-length epimerase is predicted to have a type II transmembrane topology with a 17-amino acid transmembrane domain and an 11-amino acid cytoplasmic tail. An assay with increased sensitivity was devised that detects enzyme activity in extracts prepared from cultured cells and in recombinant proteins. Unlike other enzymes involved in glycosaminoglycan biosynthesis, the addition of a c-myc tag or green fluorescent protein to the highly conserved COOH-terminal portion of the protein inhibits its activity. The amino-terminally truncated epimerase does not localize to any cellular compartment, whereas the full-length enzyme is in the Golgi, where heparan sulfate synthesis is thought to occur.

Selective bystander proliferation of memory CD4+ and CD8+ T cells upon NK T or T cell activation

Ag-experienced or memory T cells have increased reactivity to recall Ag, and can be distinguished from naive T cells by altered expression of surface markers such as CD44. Memory T cells have a high turnover rate, and CD8(+) memory T cells proliferate upon viral infection, in the presence of IFN-alphabeta and/or IL-15. In this study, we extend these findings by showing that activated NKT cells and superantigen-activated T cells induce extensive bystander proliferation of both CD8(+) and CD4(+) memory T cells. Moreover, proliferation of memory T cells can be induced by an IFN-alphabeta-independent, but IFN-gamma- or IL-12-dependent pathway. In these conditions of bystander activation, proliferating memory (CD44(high)) T cells do not derive from activation of naive (CD44(low)) T cells, but rather from bona fide memory CD44(high) T cells. Together, these data demonstrate that distinct pathways can induce bystander proliferation of memory T cells.

Facing two T cell epitopes: a degree of randomness in the primary response is lost upon secondary immunization

We have analyzed the hierarchy of epitope-specific T cell populations during a primary and a secondary CD8 T cell response. MHC-peptide tetramers were used to track the in vivo kinetics of expansion of T cell populations specific for two Kd-restricted epitopes simultaneously presented by a murine tumor cell following primary or recall immunizations. Individual syngeneic mice generated remarkably different primary CTL responses, as reflected by up to 60-fold differences in the relative contribution of each peptide-specific T cell population to the overall response. In these primary immunizations, the CTL dominance was not dictated by the respective abundance of the presented epitopes. In sharp contrast, the secondary response was systematically associated with a selective expansion of the same epitope-specific population both in vitro and in vivo. In vitro experiments indicated that the extent of expansion of each epitope-specific memory population is modulated by the epitope density. We conclude that, at least for this set of epitopes, the CTL hierarchy is not controlled by the same parameters in a primary vs a secondary response.

Melphalan and other anticancer modalities up-regulate B7-1 gene expression in tumor cells

In this study, we show that administration of low-dose melphalan (l -PAM, l -phenylalanine mustard) to mice bearing a large MOPC-315 plasmacytoma led to a rapid up-regulation of B7-1 (CD80), but not B7-2 (CD86), expression on the surface of MOPC-315 tumor cells. This l -PAM-induced preferential up-regulation of B7-1 surface expression was due, at least in part, to a direct effect of l -PAM on the tumor cells, as in vitro exposure of MOPC-315 tumor cells to l -PAM led to the preferential up-regulation of B7-1 surface expression. Moreover, in vitro exposure of MOPC-315 tumor cells to two other anticancer modalities, gamma-irradiation and mitomycin C, resulted in the preferential up-regulation of B7-1 surface expression. This effect was not restricted to MOPC-315 tumor cells, as preferential up-regulation of B7-1 surface expression was observed also following in vitro exposure of the P815 mastocytoma (that is negative for both B7-1 and B7-2 surface expression) to any of the three anticancer modalities. The up-regulation of B7-1 surface expression following in vitro exposure of tumor cells to l -PAM, gamma-irradiation, or mitomycin C required de novo protein and RNA synthesis, and was associated with the accumulation of mRNA for B7-1 within 4-8 h, indicating that the regulation of B7-1 expression is at the RNA transcriptional level. These results have important implications for an additional immune-potentiating mechanism of these anticancer modalities in clinical setting.

Soluble factor and cell-cell interaction in cytostasis induced by bone marrow cells

Cell-cell interaction and soluble low-molecular-weight products are probably involved in in vitro inhibition of leukemic cell growth by bone marrow cells.

Specific subdomains of Vav differentially affect T cell and NK cell activation

The Vav protooncogene is a multidomain protein involved in the regulation of IL-2 gene transcription in T cells and the development of cell-mediated killing by cytotoxic lymphocytes. We have investigated the differential roles that specific protein subdomains within the Vav protooncogene have in the development of these two distinct cellular processes. Interestingly, a calponin homology (CH) domain mutant of Vav (CH-) fails to enhance NF-AT/AP-1-mediated gene transcription but is still able to regulate the development of cell-mediated killing. The inability of the CH- mutant to enhance NF-AT/AP-1-mediated transcription appears to be secondary to defective intracellular calcium, because 1) the CH- mutant has significantly reduced TCR-initiated calcium signaling, and 2) treatment with the calcium ionophore ionomycin or cotransfection with activated calcineurin restores NF-AT/AP-1-mediated gene transcription. The pleckstrin homology (PH) domain of Vav has also been implicated in regulating Vav activation. We found that deletion of the PH domain of Vav yields a protein that can neither enhance gene transcription from the NF-AT/AP-1 reporter nor enhance TCR- or FcR-mediated killing. In contrast, the PH deletion mutant of Vav is able to regulate the development of natural cytotoxicity, indicating a functional dichotomy for the PH domain in the regulation of these two distinct forms of killing. Lastly, mutation of three tyrosines (Y142, Y160, and Y174) within the acidic domain of Vav has revealed a potential negative regulatory site. Replacement of all three tyrosines with phenylalanine results in a hyperactive protein that increases NF-AT/AP-1-mediated gene transcription and enhances cell-mediated cytotoxicity. Taken together, these data highlight the differential roles that specific subdomains of Vav have in controlling distinct cellular functions. More broadly, the data suggest that separate lymphocyte functions can potentially be modulated by domain-specific targeting of Vav and other critical intracellular signaling molecules.

Redirected cellular cytotoxicity by infection of effector cells with a recombinant vaccinia virus encoding a tumor-specific monoclonal antibody

Cytotoxicity is an important function of the immune system that results in the destruction of cellular targets by humoral and/or cellular mechanisms. We wanted to assess the possibility of targeting the lytic function of immune cells toward cancer cells, which express the gene coding for a known tumor antigen (Ag) (GA733-2/epithelial cell adhesion molecule), using a viral vector encoding a monoclonal antibody (mAb) specific for said tumor Ag (CO17-1A). To this end, we have constructed recombinant vaccinia viruses expressing the sequences corresponding to mAb CO17-1A, which recognizes a specific Ag (GA733-2) that is present on the surface of most gastrointestinal carcinomas. The recombinant vectors encoding either a secreted or membrane-anchored form of CO17-1A mAb were used to infect effector cells, which were subsequently assessed for their cytotoxic activity. The recombinant viruses were able to infect both granulocyte-macrophage colony-stimulating factor-activated human macrophages and Ag-stimulated murine cytotoxic T lymphocytes. Infected granulocyte-macrophage colony-stimulating factor-activated macrophages were found to be able to kill GA733-2-expressing tumor cells. Likewise, infected cytotoxic T lymphocytes, although conserving their original alloreactivity, gained the capability of killing GA733-2-expressing cancer cells.

Triplet-state photophysics of aluminium phthalocyanine sensitizer in murine cancer cells

Diffuse-reflectance laser flash photolysis has been used to record transient spectra and decay kinetics of the photodynamic therapy sensitizer disulfonated aluminium phthalocyanine in two murine cancer cell lines, P815 derived from white mouse mast cells, and EL4, a lymphoblast derived from black mouse lymphocytes. In contrast to results with bacterial cells and yeasts, no transient other than the triplet state of the sensitizer was detected, suggesting that unlike the case in microbes, Type I electron-transfer processes play no role in the photodestruction of the murine cells studied.

NK cell triggering by the human costimulatory molecules CD80 and CD86

NK cell-mediated effector functions are regulated by a delicate balance between positive and negative signals. Receptors transmitting negative signals upon engagement with target cell MHC class I molecules have been characterized in detail in recent years. In contrast, less information is available about receptor-ligand interactions involved in the transmission of positive or "triggering" signals to NK cells. Recently, it has been described that murine NK cells are triggered by the costimulatory molecules CD80, CD86, and CD40. Using NK cell lines derived from PBMC as effectors, we demonstrate that the human CD80 and CD86 gene products can function as triggering molecules for NK cell-mediated cytotoxicity. Expression of human CD80 or CD86 molecules in murine B16.F1 melanoma cells rendered these significantly more susceptible to lysis by human NK cell lines. Blocking of the transfected gene products with specific mAb reduced lysis levels to that of nontransfected control cell lines. Triggering of human NK cells by CD80 and CD86 appeared to be independent of CD28 and CTLA-4, at least as determined by the reagents used in the present study, because the expression of these molecules could not be detected on the NK cell lines by either flow cytometry or in redirected lysis assays. Thus, human NK cells may use receptors other than CD28 and CTLA-4 in their interactions with CD80 and CD86 molecules. Alternatively, interactions may involve variants of CD28 (and possibly CTLA-4) that are not recognized by certain anti-CD28 mAb.

Matrix metalloproteinase-9 production, a newly identified function of mast cell progenitors, is downregulated by c-kit receptor activation

Mast cell precursors invade from the peripheral blood into local tissues where they differentiate to their mature phenotypes. However, the mechanism of this migration process has been unclear. We clearly demonstrated here the production and release of matrix metalloproteinase-9 (MMP-9), a matrix-degrading enzyme necessary for leukocyte transmigration, by interleukin-3-dependent mouse mast cell progenitors: bone marrow-derived cultured mast cells and IC-2 mast cells. Because several interleukin-3-independent mast cell lines with active mutations in the c-kit gene did not release MMP-9, the possible involvement of c-kit receptor activation in downregulation of MMP-9 production was predicted. c-kit receptor activation by stem cell factor led to a significant decrease in MMP-9 production of cultured mast cells and IC-2 mast cells transfected with the c-kit gene. Thus, the present results suggest that mast cell precursors are able to produce MMP-9, which may be essential for mast cell migration into tissues, and that stem cell factor may downregulate the MMP-9 production, resulting in engagement of mast cells to matrix components.

Disruption of CD154:CD40 blocks generation of allograft immunity without affecting APC activation

CD154 (CD40 ligand, gp39) interaction with its receptor CD40 has been shown to be critically important for the generation of cell-mediated as well as humoral immunity. It has been proposed that ligation of CD40 on APCs, presumably by activated Th cells, leads to increased APC function as defined by up-regulation of costimulatory molecules and enhancement of IL-12 production. In this report, we directly examined the contribution of the CD154:CD40 pathway in a murine model of allograft rejection. Generation of both the CTL and alloantibody responses following injection with allogeneic P815 tumor cells was severely compromised in CD154 knockout mice and wild-type C57BL/6 mice treated with the anti-CD154 mAb, MR1. Splenic production of IL-2, IFN-gamma, and TNF was significantly suppressed from CD154-deficient mice, indicating a lack of T cell priming. However, splenic cells from CD154 knockout mice induced comparable levels of CD86 expression and IL-12 production when compared with their wild-type littermates. The treatment of CD154-/- mice with the agonistic anti-CD40 mAb, FGK45, generated activated APCs yet failed to restore either the CTL or alloantibody responses to P815. Likewise, immunization with B7-transfected P815 tumor cells failed to generate expansion of the CTL effector population in CD154-/- mice. These results suggest that the generation of allograft immunity is dependent on the interaction of CD154 with CD40 but not primarily for the activation of APCs.

Regulation of type V phospholipase A2 expression and function by proinflammatory stimuli

Types IIA and V secretory phospholipase A2 (sPLA2) are structurally related to each other and their genes are tightly linked to the same chromosome locus. An emerging body of evidence suggests that sPLA2-IIA plays an augmentative role in long-term prostaglandin (PG) generation in cells activated by proinflammatory stimuli; however, the mechanism underlying the functional regulation of sPLA2-V remains largely unknown. Here we show that sPLA2-V is more widely expressed than sPLA2-IIA in the mouse, in which its expression is elevated by proinflammatory stimuli such as lipopolysaccharide. In contrast, proinflammatory stimuli induced sPLA2-IIA in marked preference to sPLA2-V in the rat. Cotransfection of sPLA2-V with cyclooxygenase (COX)-2, but not with COX-1, into human embryonic kidney 293 cells dramatically increased the interleukin-1-dependent PGE2 generation occurring over a 24 h of culture period. Rat mastocytoma RBL-2H3 cells overexpressing sPLA2-V exhibited increased IgE-dependent PGD2 generation and accelerated beta-hexosaminidase exocytosis. These results suggest that sPLA2-V acts as a regulator of inflammation-associated cellular responses. This possible compensation of sPLA2-V for sPLA2-IIA in many, if not all, tissues may also explain why some mouse strains with natural disruption of the sPLA2-IIA gene exhibit few abnormalities during their life-spans.

CD94/NKG2-A inhibitory complex blocks CD16-triggered Syk and extracellular regulated kinase activation, leading to cytotoxic function of human NK cells

The CD94/NKG2-A complex is the inhibitory receptor for the nonclassical MHC class I molecule HLA-E on human NK cells. Here we studied the molecular mechanisms underlying the inhibitory activity of CD94/NKG2-A on NK cell functions by analyzing its interference on CD16-initiated signaling pathways involved in the control of cytolytic activity. Both tyrosine phosphorylation and activation of Syk kinase together with tyrosine phosphorylation of CD16 receptor zeta subunit are markedly inhibited by the coengagement of CD94/NKG2-A complex. As a downstream consequence, CD94/NKG2-A cross-linking impairs the CD16-induced activation of extracellular regulated kinases (ERKs), a pathway involved in NK cytotoxic function. The block of ERK activation is exerted at an early, PTK-dependent stage in the events leading to p21ras activation, as the CD16-induced tyrosine phosphorylation of Shc adaptor protein and the formation of Shc/Grb-2 complex are abrogated by CD94/NKG2-A simultaneous engagement. Our observations indicate that CD94/NKG2-A inhibits the CD16-triggered activation of two signaling pathways involved in the cytotoxic activity of NK cells. They thus provide molecular evidence to explain the inhibitory function of CD94/NKG2-A receptor on NK effector functions.

Lipopeptide particles as the immunologically active component of CTL inducing vaccines

Using a bipalmitoylated lipopeptide consisting of an ovalbumin helper T-cell epitope covalently linked to an influenza virus cytotoxic T-lymphocyte (CTL) epitope, we addressed possible factors that may be critical for CTL induction. Antigen processing of lipopeptide appears to be required for T-cell induction since there was virtually no in vitro binding of lipopeptide to purified MHC molecules. A major portion of lipopeptide immunogenicity was due to its particulate nature inasmuch as CTL induction in mice correlated with insoluble lipopeptide constructs, whereas more soluble analogs were significantly less immunogenic. Immunohistological analysis of tissue from immunized animals revealed that lipopeptide migration from the s.c. injection site to the spleen could be detected as early as 1 h after immunization and cell-associated lipopeptide was observed on macrophages and dendritic cells, implicating both cell populations in the processing and presentation of lipopeptide particles to CTLs.

A transforming mutation enhances the activity of the c-Kit soluble tyrosine kinase domain

An activating mutation (DY814) located in the catalytic domain of the c-Kit receptor has been found in mastocytomas from human, mouse and rat. We evaluated the enzymic properties of purified wild-type (WT) and DY814 tyrosine kinase domains expressed in Pichia pastoris. A linker encoding the Flag epitope was fused to c-Kit cDNA species, enabling affinity purification of the proteins with anti-Flag antibodies. Yeast lysates expressing DY814 contained multiple tyrosine-phosphorylated proteins, whereas WT lysates had no detectable tyrosine phosphorylation. Purification of the WT and mutant kinases in the presence of vanadate demonstrated that both enzymes undergo autophosphorylation. Kinetic analyses of WT and DY814 kinases indicated that at 20 nM enzyme concentration the mutation increases the specific activity 10-fold and decreases the apparent Km for ATP 9-fold. WT activity displayed a hyperbolic dependence on enzyme concentration, consistent with a requirement for dimerization or aggregation for activity. This activity was also enhanced by anti-Flag antibodies. In contrast, the dependence of DY814 activity on enzyme concentration was primarily linear and only marginally enhanced by anti-Flag antibodies. Gel-filtration analysis showed that the WT kinase migrated as a monomer, whereas the DY814 mutant migrated as a dimer. These results indicate that this point mutation promotes dimerization of the c-Kit kinase, potentially contributing to its transforming potential in mast cells.

CTLA-4 (CD152) inhibits the specific lysis mediated by human cytolytic T lymphocytes in a clonally distributed fashion

Since the functional outcome of effector T lymphocytes depends on a balance between activatory and inhibitory receptors, we studied the ability of CTLA-4 (CD152) to inhibit the cytolytic function of CTL. In 22 TCR alpha/beta+ CD3+ 8+ CTL clones, activation induced by anti-CD3, anti-CD28, or anti-CD2 mAb was inhibited by anti-CD152 mAb in a redirected killing assay. In eight clones inhibition was >40%, in 10 it ranged between 20-40%, and in four it was <20%. This suggests the existence of a clonal heterogeneity as well as for the ability of CTLA-4 to inhibit CD3/TCR-, CD28-, or CD2-mediated CTL activation. To support further this contention, we used an experimental model based upon Ag-specific CTL. Eight Ag-specific T cell clones that lyse autologous EBV-infected B lymphocytes, but are unable to lyse allogeneic EBV-infected B cell lines, were used in a cytolytic assay in which anti-CD152 mAb or soluble recombinant receptor (i.e., CTLA-4 Ig) were included. In this system, at variance from the redirected killing assay, cross-linking of surface molecules by mAb does not occur. Thus, addition of anti-CD152 mAb or of CTLA-4 Ig and anti-CD80/CD86 mAb to the assay should result in a blockade of receptor/ligand interactions. As a consequence, inhibition of a negative signal, such as that delivered via CD152, should enhance lysis. A >40% increment of target cell lysis was achieved in three of eight clones studied. Since it is not equally shared by all CTL clones, this feature also appears to be clonally distributed.

CCAAT displacement protein (CDP/cut) binds a negative regulatory element in the human tryptophan hydroxylase gene

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin, a neurotransmitter that has been implicated in many psychiatric illnesses. The mechanism of transcriptional regulation of the human TPH gene is largely unknown. We have identified a negative regulatory element located between nucleotides -310 and -220 in the human TPH (hTPH) gene. Electromobility shift analyses performed with the -310/-220 hTPH probe and nuclear extract from P815-HTR (a TPH-expressing cell line) revealed two slow migrating protein-DNA complexes, designated I and II. CCAAT displacement protein (CDP/Cut) is involved in complex I formation as shown in electromobility shift analysis, using consensus oligonucleotide competitor and antibody. Mutations in the CDP/Cut binding site not only disrupted the CDP-DNA complex but also disrupted the second complex, suggesting that the core binding sequences of the two proteins are overlapping. The functional importance of these protein-DNA interactions was assessed by transiently transfecting wild-type and mutant pTPH/luciferase reporter constructs into P815-HTR cells. Mutations in the core CDP/Cut site resulted in an approximately fourfold increase in relative luciferase activities. Because CDP/Cut has been shown to repress transcription of many target genes, we speculate that disruption of the CDP/Cut binding was responsible, at least in part, for the activation of hTPH gene.

Polyclonality and multispecificity of the CTL response to a single viral epitope

The molecular anatomy of an immunodominant, Ld restricted CTL epitope located between residues 28-39 in hepatitis B surface Ag was defined to explore the immunologic constraints on mutational escape from the CTL response during a viral infection. Using a panel of hepatitis B surface Ag residue 28-39-specific CTL clones, the response to this epitope was found to be extremely diverse at the level of TCR fine specificity and beta-chain usage. Although each clone recognized shared as well as unique residues within the epitope as TCR contact sites, even the shared residues were recognized differently by different TCRs. Despite these differences, all clones were comparably cytolytic following Ag stimulation and produced similar amounts of antiviral cytokines previously shown to inhibit HBV replication. These results demonstrate that the CTL response to individual viral epitopes can be markedly polyclonal and multispecific, such that mutational inactivation of a single TCR contact site will not usually lead to viral escape from all CTL clones of the same epitope specificity. Given these constraints and the fact that the CTL response is usually directed against several different epitopes during most viral infections, mutational inactivation of a single epitope is not likely to be sufficient to cause viral persistence.

B7.1 is a quantitatively stronger costimulus than B7.2 in the activation of naive CD8+ TCR-transgenic T cells

Using a TCR transgenic mouse bred onto a recombinase-activating gene-2-deficient background, we have examined the influence of B7.1 and B7.2 on activation of naive, CD8+ T cells in vitro. We found that B7.1 was a more potent costimulus than B7.2 for induction of proliferation and IL-2 production by naive CD8+ T cells. This difference appeared to be quantitative in nature, as determined using transfectants expressing various defined levels of B7.1 or B7.2, or using purified B7.1 or B7.2 fusion proteins. In contrast to the quantitative differences seen in stimulation of naive T cells, B7.1 and B7.2 were comparable in their ability to costimulate responses in T cells previously primed in vitro. In addition, primed, but not naive, T cells were capable of proliferating and producing IL-2 in response to a TCR stimulus alone, apparently in the absence of B7 costimulation. Lastly, we found that B7.1 and B7.2 were equivalently capable of driving differentiation of naive CD8+ T cells into an IL-4-producing phenotype when exogenous IL-4 was added to the primary culture or to an IFN-gamma-producing phenotype in the presence of IL-12. These results indicate that signals generated by B7.1 and B7.2 are qualitatively similar, but that B7.1 is quantitatively stronger than B7.2. Further, our results indicate that the activation state of the responding T cell may influence the efficiency with which the T cell can respond to a costimulatory signal provided by either B7.1 or B7.2.

A neoplastic connective tissue mast cell capable of continuous growth in tissue culture

A neoplastic connective tissue mast cell from a dog mast cell sarcoma has been grown in tissue culture for 50 passages over a period of 2 years. The cells were grown as monolayer cultures in glass bottles, using Eagle's basal medium fortified with calf serum. The cultures were contaminated with an Alkaligenes sp. for 10 months but finally were sterilized bacteriologically by treatment with specific antiserum combined with antibiotics. The cells grow in a fibroblastic pattern, and contain mitochondria, mast cell granules, and lipid granules or droplets. The mast cell granules stain basophilic with Giemsa's stain and metachromatically with azure A or toluidine blue. They also stain with Sudan black B and with periodic acid-Schiff stain. The interphase nuclei are vesicular, contain from 1 to 20 nucleoli, and frequently show bizarre outlines. Multinucleate cells are often seen, as are mitotic figures. Extracellular fibrous material occurs in all cultures and apparently originates from the cell surface. This material does not have the structure of connective tissue fibers and has not been identified. The cells develop an increased number of metachromatic granules when grown in medium containing heparin and an increased number of sudanophilic granules when grown in medium containing stearic acid. Only small amounts of histamine were present in the tumor from which this cell line was derived and in the cells grown in tissue culture.

Vitexicarpin, a flavonoid from the fruits of Vitex rotundifolia, inhibits mouse lymphocyte proliferation and growth of cell lines in vitro

Certain flavonoids having a C-2,3-double bond were reported to show an inhibitory activity against T-lymphocyte proliferation, but not against B-lymphocyte proliferation in vitro. In the course of these studies, vitexicarpin (3',5-dihydroxy-3,4',6,7-tetramethoxyflavone) isolated from the fruits of Vitex rotundifolia was found to show potent inhibition against lymphocyte proliferation. Vitexicarpin inhibited T-lymphocyte proliferation as well as B-lymphocyte proliferation at > 0.1 microM. IC50's were approximately 0.7 microM both for T- and B-cell proliferation. The inhibitory activity of vitexicarpin was reversible. Vitexicarpin also inhibited the growth of certain cancer cell lines, EL-4 and P815.9 (IC50 = 0.25-0.3 microM). These results suggest that vitexicarpin may be a potential therapeutic agent involved in inflammatory/immunoregulatory disorders such as rheumatoid arthritis and lymphomas.

Arrest of the cell cycle reduces susceptibility of target cells to perforin-mediated lysis

Cytotoxic T lymphocytes secrete a pore-forming cytolysin, perforin, that damages membranes of target cells. They also ligate Fas receptors on target cells and provoke apoptotic death. A20 (B lymphoma) and P815 (mastocytoma) cell lines were examined for their susceptibility to perforin-mediated lysis and to Fas-induced apoptosis after blockade of the cell cycle at the G1/S interface. Cells were arrested at the G1/S interface by inhibition of DNA synthesis with thymidine or aphidicolin. Subsequently, the treated cells were incubated either with CTL cytotoxic granules or the Fas-specific monoclonal antibody Jo-2. We show that arrest of the cell cycle at the G1/S interface markedly reduced the susceptibility of target cells to perforin-mediated lysis. In contrast, growth arrest with thymidine or aphidicolin increased susceptibility of A20 and P815 cells to Fas-mediated apoptosis. Susceptibility to lysis by intact CTLs was not affected significantly by blockade of target cells with aphidicolin or thymidine. When cells surviving exposure to perforin-containing granules were isolated on Ficoll density gradients and cell-cycle profiles were examined by flow cytometry, the ratio of G1 to G2 cells increased among the survivors exposed to granules in contrast to controls incubated with buffer alone. The data suggest that cells in G1 phase of the cell cycle are less susceptible to the perforin pathway than cells in G2 and S phases but are more susceptible to the Fas pathway.

Differential requirement for CD4 help in the development of an antigen-specific CD8+ T cell response depending on the route of immunization

Previous studies in our laboratory have shown that DBA/2 mice injected i.p. with syngeneic P815 tumor cells transfected with the HLA-CW3 gene (P815-CW3) showed a dramatic expansion of activated CD8+CD62L- T cells expressing exclusively the Vbeta10 segment. We have used this model to study the regulatory mechanisms involved in the development of the CW3-specific CD8+ response, with respect to different routes of immunization. Whereas both intradermal (i.d.) and i.p. immunization of DBA/2 mice with P815-CW3 cells led to a strong expansion of CD8+CD62L-Vbeta10+ cells, only the i.d. route allowed this expansion after immunization with P815 cells transfected with a minigene coding for the antigenic epitope CW3 170-179 (P815 miniCW3). Furthermore, depletion of CD4+ T cells in vivo completely abolished the specific response of CD8+CD62L-Vbeta10+ cells and prevented the rejection of P815-CW3 tumor cells injected i.p., whereas it did not affect CD8S+CD62L-Vbeta10+ cell expansion after i.d. immunization with either P815-CW3 or P815 miniCW3. Finally, the CW3-specific CD8+ memory response was identical whether or not CD4+ T cells were depleted during the primary response. Collectively, these results suggest that the CD8+ T cell response to P815-CW3 tumor cells injected i.p. is strictly dependent upon recognition of a helper epitope by CD4+ T cells, whereas no such requirement is observed for i.d. injection.

Increased threshold for TCR-mediated signaling controls self reactivity of intraepithelial lymphocytes

To examine the effect of self Ag on activation requirements of TCR-alphabeta intestinal intraepithelial lymphocytes (IELs), we utilized the 2C transgenic (Tg) mouse model specific for a peptide self Ag presented by class I MHC, H-2Ld. CD8alpha alpha and CD4-CD8- IELs from syngeneic (H-2b, self Ag-) and self Ag-bearing (H-2b/d, self Ag+) strains were examined for their ability to respond in vitro to P815 (H-2d) cell lines expressing the endogenous antigenic peptide, p2Ca. Proliferation, cytokine production, and CTL activity were elicited in IEL T cells isolated from self Ag- H-2b mice when stimulated with P815 cells expressing basal levels of self Ag. These responses were enhanced following the addition of exogenous p2Ca peptide and ectopic expression of the costimulatory molecule, B7-1. By comparison, IEL from self Ag-bearing mice failed to respond to basal levels of self Ag presented by P815 cells even in the presence of B7-1-mediated costimulation. However, the addition of increasing amounts of exogenous p2Ca peptide induced a response from the in vivo "tolerized" T cells. These results suggest that exposure to self Ag in vivo increased the threshold of TCR activation of Ag-exposed self-reactive IELs. The dependence of increased signal 1 to activate self-reactive IELs suggests a defect in TCR signaling that may maintain self tolerance in vivo. These data suggest that conditions that overcome signal 1 IEL defects may initiate autoreactive responses in the intestine.

Cyclosporin A increases IFN-gamma production by T cells when co-stimulated through CD28

Despite its calcineurin-inhibiting properties, cyclosporin A (CsA) can not inhibit IL-2 production when T cells are co-stimulated by CD80/CD86 on the antigen-presenting cells. We studied the in vitro effect of CsA on IFN-gamma production. Anti-CD3 monoclonal antibody (mAb) was used as the primary stimulus for activation of purified human T cells. A stimulating anti-CD28 mAb, or CD80 or CD86 on stably transfected P815 cells, provided the co-stimulatory signal. IL-2 production was hardly affected by CsA under these stimulating conditions, while IFN-gamma (at the protein and mRNA level) was markedly stimulated by CsA. The use of anti-CD3 or phorbol 12-myristate 13-acetate with ionomycin as the primary stimulus, together with costimulation through either CD28 or CD2 using transfectants with the appropriate ligands, allowed us to demonstrate that the resistance of IFN-gamma production to inhibition by CsA required both CD3 and CD28 triggering. Inhibition of IL-10 production, and to a lesser degree of IL-4 production, by CD4+ cells was responsible for the enhancement of IFN-gamma production in the presence of CsA. In conclusion, IFN-gamma production by CD28-co-stimulated CD4+ T cells is resistant to inhibition by CsA and can even be facilitated by CsA as a result of removing a negative regulatory signal which is mainly IL-10 mediated. This finding might have implications for immunosuppressive strategies based upon the use of CsA.

Expression of LFA-1 adhesion molecules on cisplatin-treated macrophages

Appropriately activated mononuclear phagocytes mediate contact-dependent tumoricidal activity. Adhesion structures involved in contact-dependent tumor cytotoxicity have not been defined. The present study was aimed at identifying the adhesion structure involved in the tumoricidal activity of cisplatin-activated murine peritoneal macrophages. Tumor cells of different histological origin were used as targets in a 24-h cytotoxicity assay. Anti-CD18 (LFA-1 beta) substantially inhibited macrophage cytotoxicity whereas anti-LFA-1 alpha marginally inhibited macrophage-mediated cytotoxicity. When combined together, almost complete inhibition of tumoricidal activity was observed. Activated macrophages showed augmented binding to target cells and anti-LFA MAb inhibited the binding of resting and activated macrophages to target cells. Cisplatin augmented the expression of LFA-1 alpha and beta integrins and LPS had no effect as assessed by immunoprecipitation. These results implicate that in cisplatin activated macrophages LFA-1 alpha and beta integrins are important molecules in contact-dependent tumoricidal activity.

Fc epsilon receptor I-associated lyn-dependent phosphorylation of Fc gamma receptor IIB during negative regulation of mast cell activation

Fc gamma RIIB are low-affinity receptors for IgG whose intracytoplasmic domain contains an immunoreceptor tyrosine-based inhibition motif (ITIM). Fc gamma RIIB inhibit cell activation triggered by receptors that signal via immunoreceptor tyrosine-based activation motifs. This inhibition requires ITIM tyrosyl phosphorylation and is correlated with the binding of SH2 domain-containing phosphatases that may mediate the inhibitory signal. In the present work, we investigated the mechanism of Fc gamma RIIB phosphorylation and its consequences in mast cells. We demonstrate that the phosphorylation of Fc gamma RIIB requires coaggregation with Fc epsilon RI and that, once phosphorylated, Fc gamma RIIB selectively recruit the inositol polyphosphate 5 phosphatase SHIP, in vivo. In vitro, however, the phosphorylated Fc gamma RIIB ITIM binds not only SHIP, but also the two protein tyrosine phosphatases, SHP-1 and SHP-2. We show that the coaggregation of Fc gamma RIIB with Fc epsilon RI does not prevent Fc epsilon RI-mediated activation of lyn and syk. Both kinases can phosphorylate Fc gamma RIIB in vitro. However, when coaggregated with Fc epsilon RI, Fc gamma RIIB was in vivo phosphorylated in syk-deficient mast cells, but not in lyn-deficient mast cells. When Fc epsilon RI are coaggregated with Fc gamma RIIB by immune complexes, Fc epsilon RI-associated lyn may thus phosphorylate Fc gamma RIIB. By this mechanism, Fc epsilon RI initiate ITIM-dependent inhibition of intracellular propagation of their own signals.

Creating CTL targets with epitope-linked beta 2-microglobulin constructs

Eliciting a strong CTL response is dependent upon displaying suitably high levels of specific class I MHC/peptide complexes at the cell surface. In an effort to enhance the presentation of defined CTL target structures, two unique peptide-linked beta 2-microglobulin (beta 2m) molecules were constructed. The first, designated NP(366-374)-L8-h beta 2m, links the carboxyl terminus of the H-2Db-restricted influenza nucleoprotein (NP) epitope NP(366-374) to the amino terminus of h beta 2m through an eight-amino acid glycine/serine linker. The second molecule, designated NP(147-155)-L12-h beta 2m, similarly couples the H-2Kd-restricted influenza NP epitope NP(147-155) to h beta 2m via a 12-residue polypeptide linker. Transfection of the NP(366-374)-L8-h beta 2m vector into H-2b-expressing cell lines sensitized these cells for lysis by NP(366-374)-specific CTLs. Free NP peptide could not be detected when class I bound peptides were acid-extracted from the surface of NP(366-374)-L8-h beta2m transfectants, indicating that CTL killing was mediated by recognition of the peptide linked to h beta 2m and not by a degradation by-product. CTL target structure formation was also achieved by an exogenous presentation pathway. H-2d-expressing target cells were sensitized for lysis when pulsed with NP(147-155)-L12-h beta 2m protein derived from an Escherichia coli cell lysate. The effect of recombinant NP(147-155)-L12-h beta 2m was inhibited by competitor wild-type h beta 2m, indicating that the active peptide-h beta 2m fusion protein remained intact. The observation that beta 2m with covalently attached peptide can effectively create CTL target structures in vitro offers new possibilities for the in vivo induction of epitope-specific CTL responses by either DNA immunization or injection of the purified epitope-linked beta 2m.

Differential processing of influenza nucleoprotein in human and mouse cells

To investigate how early events in antigen processing affect the repertoire of peptides presented by MHC class I molecules, we compared the presentation of the influenza A nucleoprotein epitope 265-273 by HLA-A3 class I molecules in human and mouse cells. Mouse cells that express HLA-A3 failed to present the NP265-273 peptide when contained within the full-length nucleoprotein, to HLA-A3-restricted human cytotoxic T lymphocytes. However, when the epitope was generated directly in the cytosol using a recombinant vaccinia virus that expressed the nonamer peptide, mouse cells were recognized by HLA-A3-restricted CTL. Poor transport of the peptide by mouse TAP was not responsible for the defect as co-infection of mouse cells with recombinant vaccinia viruses encoding the full-length nucleoprotein and the human TAP1 and TAP2 peptide transporter complex failed to restore presentation. These results therefore demonstrate a differential processing of the influenza nucleoprotein in mouse and human cells. This polymorphism influences the repertoire of peptides presented by MHC class I molecules at the cell surface.

Immunostimulatory effects of a plasmid expressing CD40 ligand (CD154) on gene immunization

Interaction of CD40 with its ligand (CD154) can induce CD40-bearing APCs to express immune stimulatory accessory molecules that facilitate immune recognition. We evaluated whether a plasmid vector encoding CD154 (pCD40L) could influence the immune response to a transgene protein encoded by coinjected plasmid DNA. We found that coinjection of pCD40L in BALB/c mice enhanced the Ab response to beta-galactosidase induced by i.m. or intradermal injection of placZ, a plasmid DNA vector encoding beta-galactosidase. Furthermore, i.m. or intradermal coinjection of pCD40L with placZ enhanced the generation of CTL specific for P815 cells transfected with placZ. This study indicates that pCD40L can serve as a genetic adjuvant capable of augmenting humoral and cellular immune responses to Ags encoded by plasmid DNA expression vectors.

Deoxyribonucleic acid vaccines encoding antigens with rapid proteasome-dependent degradation are highly efficient inducers of cytolytic T lymphocytes

We generated plasmid expression vectors encoding ubiquitin and beta-galactosidase (beta-gal) with different intervening amino acids, allowing for the production of processed protein products that have either stabilizing or destabilizing residues at their N-termini. P815 cells transfected with plasmids encoding beta-gal with a destabilizing N-terminus did not have detectable expression beta-gal unless they were treated with inhibitors specific for the proteasome. Inhibitors of other proteolysis pathways had no such effect. Nevertheless, transfectants expressing beta-gal with different amino acid residues were equally sensitive to cytolysis by a CTL clone specific for a beta-gal peptide presented in the context of H-2Ld. In contrast to vectors encoding native beta-gal, plasmid vectors encoding beta-gal with a destabilizing residue did not induce detectable anti-beta-gal Abs when injected into skeletal muscle of BALB/c mice. However, such vectors were significantly more effective than vectors encoding native beta-gal or beta-gal with a stabilizing residue in stimulating CTL specific for P13.2, a lacZ transfectant of P815. We conclude that incorporation of strategies that enhance proteasome-dependent degradation may generate DNA vaccines that are more effective in inducing cellular immunity against targeted Ags.

In vitro- and ex vivo-derived cytolytic leukocytes from granzyme A x B double knockout mice are defective in granule-mediated apoptosis but not lysis of target cells

Granzyme (gzm) A and gzmB have been implicated in Fas-independent nucleolytic and cytolytic processes exerted by cytotoxic T (Tc) cells, but the underlying mechanism(s) remains unclear. In this study, we compare the potential of Tc and natural killer (NK) cells of mice deficient in both gzmA and B (gzmAxB-/-) with those from single knockout mice deficient in gzmA (-/-), gzmB (-/-), or perforin (-/-) to induce nuclear damage and lysis in target cells. With the exception of perforin-/-, all in vitro- and ex vivo-derived Tc and NK cell populations from the mutant strains induced 51Cr-release in target cells at levels and with kinetics similar to those of normal mice. This contrasts with their capacity to induce apoptotic nuclear damage in target cells. In gzmAxB-/- mice, Tc/NK-mediated target cell DNA fragmentation was not observed, even after extended incubation periods (10 h), but was normal in gzmA-deficient and only impaired in gzmB-deficient mice in short-term (2-4 h), but not long-term (4-10 h), nucleolytic assays. This suggests that gzmA and B are critical for Tc/NK granule- mediated nucleolysis, with gzmB being the main contributor, while target cell lysis is due solely to perforin and independent of both proteases.

Down-regulation of the expression and function of the transporter associated with antigen processing in murine tumor cell lines expressing IL-10

The MHC class I molecules present antigenic peptides to CTL. The peptides are delivered to the secretory pathway by TAP, which is formed by the association of MHC-encoded TAP1 and TAP2 gene products. Tumor cells incubated or transfected with IL-10 had decreased but peptide-inducible expression of MHC class I, decreased sensitivity to MHC class I-restricted CTL, and increased NK sensitivity. We here demonstrate that IL-10 expression in the murine lymphoma RMA inhibits the TAP-dependent translocation of peptides to the endoplasmic reticulum, resulting in accumulation of immature MHC class I molecules in the endoplasmic reticulum and subsequently low expression of cell surface MHC class I molecules. This finding is explained by a down-regulation of expression of TAP1 and TAP2, observed in IL-10-transfected RMA cells as well as in IL-10-transfected P815 mastocytoma cells. In the J558L plasmacytoma cell line, constitutively expressing high levels of IL-10, increased TAP-dependent translocation of peptides and expression of cell surface MHC class I could be induced by IL-10 antisense expression. IL-10 is the first example to demonstrate that a cytokine can decrease the expression and function of the TAP1/2 molecular complex and, in more general terms, the first example of a cytokine with an inhibitory effect on MHC class I-mediated Ag presentation.

Chronic ethanol effects on cellular immune responses to hepatitis B virus envelope protein: an immunologic mechanism for induction of persistent viral infection in alcoholics

Hepatitis B virus (HBV) is common in alcoholics and may result in chronic infection. Persistence of HBV infection could be partially caused by the effects of ethanol on the cellular and humoral immune response to viral structural proteins. The DNA-based immunization approach was used to experimentally assess the effects of chronic ethanol feeding on immune responses directed against the middle envelope protein (MHBs) of HBV. Mice were fed an ethanol or isocaloric, pair-fed control liquid diet for 8 weeks, followed by immunization with a plasmid construct containing the pre-S2/S gene that encodes for MHBs. Chronic ethanol consumption marginally reduced the levels of the antibody to hepatitis B surface proteins (anti-HBs) generated by the DNA-based immunization approach. Initially, cytotoxic lymphocyte (CTL) activity was higher in ethanol-fed mice but progressively declined following the second and third immunizations as compared with control mice. In addition, CTL and CD4+ T helper (TH) cells responded poorly to increasing concentrations of envelope protein and peptides in vitro with respect to generation of CTL activity and proliferative responses. Finally, proliferating CD4+ T cells derived from ethanol-fed animals had substantial changes in the levels of cytokines secreted into the culture supernatants as compared with control mice. These studies show that chronic ethanol consumption substantially alters the cellular immune responses to a human viral structural protein, and that these effects may contribute to the persistence of viral infection.

Peptides derived from a wild-type murine proto-oncogene c-erbB-2/HER2/neu can induce CTL and tumor suppression in syngeneic hosts

In this analysis, we examined whether peptides derived from a wild-type murine proto-oncogene, c-erbB-2, function as tumor rejection Ags. Expression of murine c-erbB-2 examined by means of reverse transcription-PCR was observed in several normal adult tissues, such as intestine, kidney, and testis. We then transduced human and murine c-erbB-2 cDNA into two mutually noncross-reactive fibrosarcoma lines of BALB/c origin, CMS7 and CMS17. In BALB/c mice immunized with CMS17HE (CMS17 transduced with human c-erbB-2 cDNA), the growth of subsequently challenged CMS7HE (CMS7 transduced with human c-erbB-2 cDNA) was significantly suppressed. CTL against human c-erbB-2-expressing cells were generated from BALB/c spleen cells in vivo and in vitro sensitized by CMS17HE. The CTL activity was also directed against murine c-erbB-2-expressing cells, CMS7ME and CMS17ME, and was blocked by anti-CD8 or anti-Kd mAbs. A series of peptides of human or murine c-erbB-2 compatible with the Kd binding motif was synthesized. The CTL were reactive with P1.HTR (H-2d) pulsed with three of these peptides, p63-71 (human c-erbB-2 derived), p63-71(A) (murine c-erbB-2 derived), and p780-788 (common for human and murine c-erbB-2). Spleen cells immunized in vivo and in vitro with syngeneic spleen cells pulsed with these peptides became cytotoxic for CMS17HE and/or CMS17ME, but not CMS17neo (CMS17 transduced with control vector). The growth of CMS7ME was suppressed in mice immunized with the murine c-erbB-2-derived peptide, p63-71(A) or p780-788. There was no apparent pathologic change in mice that rejected CMS7ME after vaccination with these peptides.

PGE2, but not TGF beta 2, in rabbit blastocoelic fluid regulates the cytotoxic activities of NK and LAK cells

Spontaneous and induced fetal resorptions have been associated with the infiltration and activation of GM1-positive natural killer (NK)-like cells. Predominance of these cells in the decidua and their reduced lytic activity suggest that regulation of their killing activity could be important for the survival of the fetus. It has therefore been hypothesized that the embryo was regulating NK lytic activity. To test this hypothesis, human and rabbit lymphocytes were cultured with various concentrations of interleukin-2. Their ability to kill 51Cr-labelled NK and lymphokine-activated killer (LAK)-sensitive targets was assessed in the presence of rabbit blastocoelic fluid taken at day-12 of pregnancy (BF D-12). BF D-12 dramatically suppressed the killing activity of NK and LAK cells. This effect was observed on K562 (NK-sensitive targets), P815 cells (LAK-sensitive targets), and freshly isolated cells in rabbit trophoblastic cell preparation. Elimination of prostaglandin E2 (PGE2), but not transforming growth factor beta 2 (TGF beta 2) or 6 keto prostaglandin F1 alpha (6KPGF 1 alpha), by affinity chromatography, completely abolished BF biological activity. These findings clearly suggest that PGE2 in BF regulates the killing activity of NK and LAK cells, and that the semiallograft embryo plays an active role in its own protection. To our knowledge, it is the first demonstration that PGE2 from the embryo inhibits NK and LAK cell lytic activity.

Mechanisms of constitutive activation of c-kit receptor tyrosine kinase

We investigated the mechanism of constitutive activation of c-kit receptor tyrosine kinase (KIT) found in the FMA3 murine mastocytoma cell line, and compared it with the mechanisms observed in other tumor mast cell lines (the HMC-1 human mast cell leukemia cell line, the RBL-2H3 rat mast cell leukemia cell line, and the P-815 murine mastocytoma cell line). The c-kit gene obtained from FMA3 cells was found to have 21-base deletion at the juxtamembrane domain of KIT, thereby leading to the constitutive activation of KIT. The deletion at the juxtamembrane domain resulted in constitutive dimerization of c-kit proteins, whereas the point mutation that were detected at the kinase domain of KIT in HMC-1, RBL-2H3, and P-815 cells caused constitutive activation of KIT without dimerization. These constitutively activating mutations of c-kit may play a role in development of mast cell tumors.

Rat mast cell lines bind to the vascular cell adhesion molecule-1 (VCAM-1) and the mucosal addressin cell adhesion molecule-1 (MAdCAM-1)

Mast cells are key mediators of allergy and inflammation. Increased mast cell numbers are observed in the gut during helminth infestation and at many sites of inflammation. To determine whether mast cells express functional receptors for endothelial cell adhesion molecules, we studied the adhesion of two rat mucosal-type mast cell lines RBL-1 and RCMC-1 to transfected mucosal addressin cell adhesion molecule-1 (MAdCAM-1) and VCAM-1. Both mast cell lines expressed high levels of alpha4 integrins on their surface and bound to CHO cells transfected with VCAM-1. Anti-alpha4 mAbs, TA-2 and L25, inhibited the specific adhesion of the mast cells to VCAM-1 by about 92 and 63%, respectively. Both of the mast cell lines also demonstrated an increased adhesion to CHO cells transfected with MAdCAM-1. The adhesion of RBL-1 to MAdCAM-1 was also significantly inhibited by the anti-alpha4 mAbs TA-2, L25, and HP2/1 by 39, 76, and 42%, respectively. In addition, RBL-1 cells adhered to both VCAM-1 and MAdCAM-1 under both static and nonstatic (shear) conditions, and this was also inhibited by the anti-alpha4 mAb TA-2. Thus, mucosal-type mast cell lines express functional alpha4 integrins that can mediate adhesion to VCAM-1 and MAdCAM-1. These results suggest a mechanism for mast cell accumulation at sites of inflammation and in the gut.

The role of the CD28/B7 interaction in the regulation of NK cell responses during infection with Toxoplasma gondii

We examined the role of the CD28/B7 interaction in regulation of NK cell activity. Cells transfected with B7 enhanced IL-12-induced production of IFN-gamma by IL-2-activated, CD28+ NK cells, but not by resting CD28- NK cells. The ability of B7 transfectants to enhance NK cell production of IFN-gamma was dependent on the intracellular adhesion molecule-1/LFA-1 interaction and could be inhibited by TGF-beta, but not IL-10. Since IL-12-induced production of IFN-gamma by NK cells is associated with resistance to certain infections, we examined whether the CD28/B7 interaction regulated NK cell responses during infection. Infection of SCID mice with Toxoplasma gondii resulted in the appearance of a population of CD28+ NK cells, NK cell production of IFN-gamma, and increased NK cell cytolytic activity. Administration of CTLA4-Ig to SCID mice infected with T. gondii inhibited these latter two effects and resulted in a significant increase in parasite burden. The stimulus for CD28 expression by NK cells in SCID mice infected with T. gondii appeared to be independent of IL-2. However, mRNA for IL-15, a cytokine with properties similar to those of IL-2, was detected in tissues of SCID mice infected with T. gondii. In vitro experiments demonstrated that IL-15 could stimulate resting NK cells to express functionally active CD28 as well as enhance the production of IFN-gamma by SCID splenocytes stimulated with T. gondii. Together our data demonstrate that the interaction of CD28+ NK cells with B7 regulates NK cell production of IFN-gamma associated with resistance to infection and that IL-15 may be involved in these events.

Analysis of human common bile duct-associated T cells: evidence for oligoclonality, T cell clonal persistence, and epithelial cell recognition

The phenotype of T cells associated with the common bile duct (CBD) is unknown. We investigated the hypothesis that they behave like other intraepithelial lymphocytes (IEL). Thus, we sought to determine the phenotype, TCR repertoire, and epithelial recognition of T cells obtained during endoscopic retrograde cholangiopancreatography. Three subjects were studied: two with primary sclerosing cholangitis and one normal control. After establishing a short-term T cell line, cells were 1) stained with mAbs for flow cytometric analysis, 2) analyzed for TCRB chain transcript expression, and 3) used as effector cells for cytotoxicity and proliferation. Flow cytometry revealed that for all the subjects 98% of the T cells were TCR-alpha beta-positive. Immunohistology of the CBD showed that the epithelium and lamina propria contained significant numbers of CD3+ CD43+ CD45RO+ lymphocytes. Complementarity-determining region 3 length displays suggested that the CBD-derived lines were oligoclonal. This was confirmed by cloning and random sequencing of PCR amplification products using TCRBV region family-specific primers; TCRB chain sequences were reiterated in all transcripts analyzed. In one case, two expanded TCRB clones could be identified that were persistent in the bile duct over a 1-yr period. The CBD-derived lines were cytolytic in a redirected lysis assay and caused cytolysis of an intestinal epithelial cell line (Caco-2). This recognition was likely preferential for intestinal epithelial cells, since a CBD-derived line exhibited proliferation to two intestinal epithelial cell lines (HT-29 and Caco-2) but not three other lines (HepG2, human foreskin fibroblast, and KD). We conclude that the CBD contains IELs that share several characteristics with intestinal IELs.

Aggregation of low affinity IgG receptors induces mast cell adherence to fibronectin: requirement for the common FcR gamma-chain

Mast cells have been reported to increase at sites of immune complex-induced inflammation where these cells appear to potentiate the inflammatory response. The mechanism by which mast cells accumulate at these sites is unknown. One possibility is that aggregation of low affinity IgG receptors could signal mast cells to adhere to components of the connective tissue matrix. To test this hypothesis, we first added aggregated IgG to a mast cell adhesion assay employing fibronectin as a matrix component and observed an increase in cell adhesion. Even a small amount of aggregated IgG (< 60 ng/ml) demonstrated by fast protein liquid chromatography in untreated IgG preparations was sufficient to increase mast cell adhesion by 100%. We next explored the Fc gamma receptors involved. Fc gammaRII/III, which are receptors for oligomeric IgG and were first verified as present on these mast cells by FACS analysis and immunoprecipitation, signaled mast cells to rapidly adhere to fibronectin when aggregated with the anti-receptor Ab2.4G2. The adhesion process mediated by Fc gammaRII/III was not associated with beta-hexosaminidase release. Bone marrow-cultured mast cells from common gamma-chain deficient mice, unlike mast cells cultured from +/+ mice, did not respond to Fc gammaRII/III aggregation. This demonstrated requirement for a gamma-chain implicates oligomeric Fc gammaRIII in the adhesion process. Thus, aggregation of Fc gammaRIII on mast cells leads to mast cell adhesion, demonstrating a previously unknown biological function for this receptor on mast cells and providing a mechanism for mast cell accumulation in immune complex-dependent inflammation.

CD56bright natural killer cell subsets: characterization of distinct functional responses to interleukin-2 and the c-kit ligand

Natural killer (NK) cells are bone marrow-derived large granular lymphocytes that express the CD56 surface antigen. The CD56bright NK subset represents approximately 10% of all NK cells and is thought to be the least differentiated NK cell component in blood. The most mature NK cell expresses CD56 at low density and CD16 (FcR gammaIII) at high density, whereas CD56bright NK cells either lack CD16 (CD56bright CD16-) or express it at low density (CD56bright CD16dim). c-kit is a tyrosine kinase receptor which is expressed on both CD34+ hematopoietic precursor cells and CD56bright NK cells. In the current study, we characterize interleukin (IL)-2 receptor (IL-2R) and c-kit expression in each of the CD56bright subsets. Both the CD56bright CD16- and CD56bright CD16dim NK subsets express the high-affinity IL-2R and the c-kit receptor when isolated from fresh blood. However, each CD56bright NK cell subset has distinct functional responses to IL-2, the c-kit ligand (KL), or both. Activation of the high-affinity IL-2R on CD56bright CD16- NK cells induces a proliferative response that is significantly weaker than that observed in the CD56bright CD16dim NK cell subset. Incubation of the CD56bright CD16 NK cell subset with KL significantly enhances IL-2-induced proliferation, while KL has no such effect on the CD56bright CD16dim NK subset. Activation of the high-affinity IL-2R in both CD56bright subsets induces lymphokine-activated killer (LAK) activity, but the addition of KL has no effect on LAK activity. Co-stimulation of either CD56bright subset with IL-12 and concentrations of IL-2 that only saturate the high-affinity IL-2R induces substantial interferon (IFN)-gamma production. The addition of KL to this co-stimulatory signal enhances IFN-gamma production in both CD56bright NK subsets. The distinct functional responses to IL-2 and KL seen in the CD56bright CD16- and CD56bright CD16dim NK subsets provide insight into IL-2R signaling and suggest that each phenotype identifies a discrete stage of NK cell differentiation.

Immunological studies of SK2 hybridoma cells microencapsulated with alginate-poly(L)lysine-alginate (APA) membrane following allogeneic transplantation

Microencapsulation of living cells or tissues has been proposed to prevent their immune destruction following transplantation. In this study, we examined whether SK2 hybridoma cells microencapsulated in an alginate-poly(L)lysine-alginate (APA) membrane (APA-SK2 cells) were immunoisolated from the allogeneic host's immune system using a cytotoxicity test. The APA membrane inhibited the activation of the host's cellular immune response, but did not prevent the production of cytotoxic antibodies against entrapped SK2 cells following allogeneic transplantation. However, the APA-SK2 cells remained vital in SK2 cell-immunized mice as well as in intact mice. We considered that complement regulatory factors which were present on cell membrane and had species-specific restriction blocked the complement-mediated cell lysis on allogeneic transplantation, since APA-SK2 cells were destroyed by rabbit anti-SK2 cell antiserum. Our results demonstrated that APA membrane could inhibit cell-cell contact between entrapped cells and the host's lymphocytes, but could not completely protect the entrapped cells from xenogeneic humoral immunity.

Poxvirus-based Japanese encephalitis vaccine candidates induce JE virus-specific CD8+ cytotoxic T lymphocytes in mice

Recombinant Japanese encephalitis (JE) vaccine candidates based on a highly attenuated vaccinia virus (NYVAC-JEV) and a canarypox virus (ALVAC-JEV) were evaluated for their ability to induce specific antibodies and cytotoxic T lymphocytes (CTLs) in mice. Six- to eight-week-old male Balb/c mice that received one or two intraperitoneal inoculations with these JE vaccine candidates at a dose of 1 x 10(7) PFU per mouse produced neutralizing antibody and antibodies to the envelope (E) and nonstructural 1 (NS1) proteins as determined by radioimmunoprecipitation. Immunization with either of these vaccine candidates also induced JE virus-specific T lymphocytes that proliferated in response to stimulation with infectious virus and/or noninfectious viral antigens. Mice maintained detectable levels of neutralizing antibody and JE virus-specific memory T cells for at least 6 months after immunization with NYVAC-JEV and for 4 months after immunization with ALVAC-JEV. Cells induced to proliferate after stimulation with live virus contained specific CD8+ CTLs that lysed primary Balb/c mouse kidney cells infected with JE virus and P815 mastocytoma cells infected with a recombinant vaccinia virus expressing the premembrane (prM), E, and NS1 proteins. These CTLs also lysed P815 cells infected with vaccinia recombinants expressing prM and E, and those expressing E and NS1, but did not lyse P815 cells infected with a recombinant virus expressing only NS1, indicating that the CTLs mainly recognized E, but did not recognize NS1. These results demonstrate that both recombinant JE vaccines, NYVAC-JEV and ALVAC-JEV, induce JE virus-specific antibody and CTLs in mice.