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B T Huber

Publications and source records attributed to B T Huber.

At least 55 records · Page 3Linked to original sources
PubMed1994

Binding sites for bacterial and endogenous retroviral superantigens can be dissociated on major histocompatibility complex class II molecules.

Bacterial and retroviral superantigens (SAGs) interact with major histocompatibility complex (MHC) class II molecules and stimulate T cells upon binding to the V beta portion of the T cell receptor. Whereas both types of molecules exert similar effects on T cells, they have very different primary structures. Amino acids critical for the binding of bacterial toxins to class II molecules have been identified but little is known of the molecular interactions between class II and retroviral SAGs. To determine whether both types of superantigens interact with the same regions of MHC class II molecules, we have generated mutant HLA-DR molecules which have lost the capacity to bind three bacterial toxins (Staphylococcus aureus enterotoxin A [SEA], S. aureus enterotoxin B [SEB], and toxic shock syndrome toxin 1 [TSST-1]). Cells expressing these mutated class II molecules efficiently presented two retroviral SAGs (Mtv-9 and Mtv-7) to T cells while they were unable to present the bacterial SAGs. These results demonstrate that the binding sites for both types of SAGs can be dissociated.

Animals↗
PubMed1994

Expression of Mtv-7 sag gene in vivo using a retroviral vector results in selective inactivation of superantigen reactive T cells.

T cells expressing specific TCR V beta chains are intrathymically eliminated in mice expressing the murine Mls (minor lymphocyte stimulating) superantigens. Recently, in vitro studies have shown that the endogenous mouse mammary tumor virus (MMTV)-7 sag gene encodes Mls-1 Ag. The demonstrated ability of MMTV superantigen proteins to react with TCRs has led to the postulate that other infectious retroviruses may use superantigen-like molecules to modify the host's immune system. In this report, successful retrovirus-mediated Mtv-7 sag gene transfer into pluripotent hematopoietic stem cells is described. In two different strains of Mls-1- host mice (CBA/Ca and BALB/c) reconstituted with Mtv-7 sag gene expressing bone marrow cells, low levels of ectopic Mtv-7 sag gene expression on syngeneic donor hematopoietic stem cell-derived population alone can induce partial clonal deletion of Mls-1 reactive V beta 6+ and V beta 8.1+ T cells, and complete clonal inactivation of V beta 8.1+ T cells.

Animals↗
PubMed1994

The role of superantigens in the immunobiology of retroviruses.

Murine mammary tumour viruses (MMTVs) are retroviruses that encode superantigens capable of stimulating T cells via superantigen-reactive T cell receptor V beta chains. MMTVs are transmitted to the suckling offspring via the milk. We have established that class II and B cell-deficient mice that were foster nursed by virus-secreting mice do not transfer infectious MMTVs to their offspring. No MMTV proviruses could be detected in the spleen and mammary tissue of these mice and there was no deletion of MMTV superantigen-reactive T cells. These results confirm that superantigen expression in the context of MHC class II molecules is required for MMTV transmission. We conclude that B cells are essential for the completion of the viral life cycle in vivo. This indicates that B cells are infected first and that viral amplification takes place only if infected B cells present the MMTV superantigen on their surface which, in turn, results in activation of T cells expressing the appropriate T cell receptor V beta chains. These activated T cells stimulate B cells which enables viral replication. Human T cells carry all the structural features required for an efficient response to murine retrovirally encoded superantigens. Superantigen-like stimulation of human T cells has been demonstrated in both infectious and autoimmune diseases. Human immunodeficiency virus may encode a superantigen but this has not been proven.

Animals↗
PubMed1993

Presentation of the Mls-1 superantigen by human HLA class II molecules to murine T cells.

Superantigens (SAG) presented in the context of MHC class II proteins stimulate a strong proliferative response in T cells expressing particular TCR V beta genes. Although this T-cell recognition is not MHC restricted, a strong hierarchy is observed in the ability of various MHC class II molecules to present SAG. Mls-1, encoded by the Murine Mammary Tumor Virus (MMTV) Mtv-7 sag gene, is the prototype of endogenous SAG. In the present study, we have analyzed whether this retroviral gene product can be presented in the context of human HLA class II proteins to murine T cells. Positive results were obtained with the DR isotype and in in vitro, as well as in vivo T-cell stimulation assays. However, the various DR beta alleles, expressed in combination with an identical DR alpha chain, differed in their Mls-1 presenting capacity, indicating that the MHC class II beta-chain contains the primary contact site for Mls-1. Interestingly, the same pattern of TCR V beta restriction was seen in response to Mls-1 presented in the context of human and mouse class II, suggesting that the TCR V beta specificity is uniquely determined by the retroviral SAG. Furthermore, Mls-1 presented in the context of the DQw1 and DPw2 isotypes did not elicit a T-cell response. The results from this study form the basis for further analysis of the exact region in the class II beta-chain that interacts with Mls-1.

Alleles↗
PubMed1993

Human T cells respond to mouse mammary tumor virus-encoded superantigen: V beta restriction and conserved evolutionary features.

Mouse mammary tumor virus (MMTV)-encoded superantigens (SAGs) influence the murine T cell repertoire and stimulate a strong mixed lymphocyte response in vitro. These SAGs are encoded by the open reading frame of the 3' long terminal repeat of MMTV, termed MMTV SAGs. The T cell response to MMTV SAGs is V beta restricted and requires expression of the class II molecules of the major histocompatibility complex (MHC) on the presenting cells. While human T cells respond to bacterial SAGs, it is not known if human T cells or human MHC class II molecules can interact with MMTV SAGs. A fibroblastic cell line expressing the human MHC class II molecule HLA-DR1 and the Mtv-7 sag gene encoding Mls-1 was used to stimulate human T cells. We show here that human T cells efficiently proliferate in response to Mls-1 presented by HLA-DR1. This T cell response was inhibited by mAbs directed against CD4 or MHC class II molecules but not by mAbs specific for CD8 or MHC class I molecules. Moreover, the response to Mls-1 was limited to human T cells expressing a restricted set of T cell receptor V beta chains. Human T cells expressing V beta 12, 13, 14, 15, and 23 were selectively amplified after Mtv-7 sag stimulation. Interestingly, these human V beta s share the highest degree of homology with the mouse V beta s interacting with Mls-1. These results show a strong evolutionary conservation of the structures required for the presentation and the response to retrovirally encoded endogenous SAGs, raising the possibility that similar elements operate in humans to shape the T cell repertoire.

Animals↗
PubMed1993

Mechanism of HIV-1 Tat induced inhibition of antigen-specific T cell responsiveness.

HIV-1 Tat has been shown to have an inhibitory effect on the Ag-specific responsiveness of human peripheral T cells. We have previously demonstrated that this retroviral protein binds to and partially inhibits the enzymatic activity of dipeptidyl aminopeptidase type IV (DP IV), also known as CD26, which is expressed on a variety of mammalian tissue, including T lymphocytes. A number of studies have implicated a role for DP IV in the activation of T lymphocytes. By utilizing HIV-1 Tat, as well as ProboroPro, a potent and specific boronic acid analog inhibitor of DP IV, we show here that blocking DP IV partially inactivates Ag and anti-CD3-mediated T cell proliferation. Neither mitogen nor anti-CD2 mediated proliferation of T lymphocytes, however, is impaired by blocking DP IV. The target molecule for the inhibition induced by both compounds was confirmed by the finding that soluble DP IV neutralized the reduced Ag responsiveness. The Ag-specific inhibition could be overcome by the addition of exogenous IL-2, suggesting that blocking or inactivation of DP IV results in a state of anergy, probably by interfering with the delivery or amplification of a signal necessary for IL-2 production. This is further substantiated by the finding that costimulation of human PBMC via the CD28 molecule, which initiates a non-TCR-dependent signaling pathway, overcomes the reduced Ag responsiveness induced by Tat and ProboroPro. The fact that ProboroPro has no impact on stimulation of T cells with PMA and ionomycin implies that blocking DP IV is influencing events before the activation of protein kinase C and Ca2+ flux. These results suggest that DP IV is necessary for amplification of signals generated by the engagement of the TCR-CD3 complex by nominal Ag.

Adult↗
PubMed1993

Production and characterization of an Mls-1-specific monoclonal antibody.

Superantigens (SAGs) represent a new class of antigens, characterized as T cell receptor (TCR) V beta-reactive elements. Bacterial toxins constitute the major group of exogenous SAGs, while the mouse mammary tumor virus (MMTV)-encoded Mls molecules represent the endogenous SAGs. Mls-1 is the prototype of the latter SAGs, because it elicits a very potent T cell stimulatory response in vitro in unprimed T cells expressing the TCR V beta 6 or 8.1 chains. In vivo, Mls-1 causes deletion of immature T cells bearing the V beta 6, 7, 8.1, or 9 chains. Although Mls-1 was functionally discovered > 20 yr ago, it has not been possible to raise antibodies against this molecule. We have previously cloned and sequenced the Mtv-7 sag gene, which encodes Mls-1. Sequence comparisons with other MMTV sag genes suggested that the polymorphic 3' end encodes the TCR V beta specificity of these SAGs. We have, therefore, immunized hamsters with a 14-amino acid peptide from the deduced COOH-terminal sequence of the Mtv-7 sag gene. We describe here the production of a monoclonal antibody (mAb), 3B12, which is peptide specific and reacts with a recombinant baculovirus product of Mtv-7 sag. This mAb blocks Mls-1-specific T cell recognition and detects the Mls-1 protein on the surface of the B cell hybridoma LBB.A, but not on LBB.11, which is an Mtv-7 loss variant of LBB.A. Transfection of the Mtv-7 sag gene into LBB.11 renders this cell functionally Mls-1+ as well as positive for 3B12 binding, confirming the specificity of this mAb. It is well documented that B cells and CD8+ T cells express T cell stimulatory Mls-1 determinants, and we show here that this functional profile correlates with the expression of MMTV-specific mRNA. However, primary lymphocytes derived from Mls-1+ mice do not stain with 3B12, even after in vitro activation with mitogens or phorbol ester.

Amino Acid Sequence↗
PubMed1992

Minor lymphocyte stimulatory antigen-bearing stimulator cells require lipopolysaccharide activation to induce programmed cell death in T cell hybridomas.

T cell hybridomas respond to conventional peptide Ag associated with self major histocompatibility restriction elements, as well as to alloantigens, activating lectins, and stimulatory forms of mAb by producing lymphokines and undergoing programmed cell death (PCD). We show here that the level of PCD and IL-2 production correlate well in responses to CD3 or allostimulation. The response to minor lymphocyte-stimulatory (Mls) Ag, members of the family of endogenous superantigens, however, are marked by divergence in the levels of the PCD and lymphokine responses. Specifically, PCD in response to Mls activation is achieved poorly despite vigorous IL-2 production. B lymphoma cell stimulators induced PCD in alloreactive T cell hybridomas but not in Mls-reactive T cell hybridomas. This suggests that the absence of PCD in the Mls response is a function of superantigen recognition rather than the stimulator cell type. LPS-preactivated Mls+ stimulators, either splenic B or B lymphoma cells, are shown to trigger PCD in the T cell hybridomas. These results imply that T cell interaction with Mls presented by untreated stimulator cells is not sufficient for induction of PCD and thus is distinct from interactions with conventional Ag.

Animals↗
PubMed1992

IL-4 and IL-2 selectively rescue Th cell subsets from glucocorticoid-induced apoptosis.

It is well established that T cell maturation and activation are negatively regulated by a mechanism termed apoptosis. We now present evidence that glucocorticoids, known to possess immunosuppressive properties, cause apoptosis in mature Th cells, similarly to what has been reported for thymocytes. Th cells treated with the synthetic glucocorticoid dexamethasone show genome fragmentation into oligonucleosomal fragments, and proliferation of growth factor stimulated Th cells is inhibited by glucocorticoids. We show that IL-4 specifically rescues Th2 cells from dexamethasone-mediated apoptosis, whereas IL-2 and IL-1 are ineffective in these cells. However, IL-2 is the relevant rescue-factor of glucocorticoid-treated Th1 cells. The rescue induced by IL-4 and IL-2 is thought to be mediated by protein kinases (possibly protein kinase C), as evidenced by the fact that the protein kinase inhibitor H7 blocks the action of IL-4 and IL-2 in glucocorticoid-treated cells. Our in vitro data show that mature T cells can be protected by their own growth factors from the deleterious effects of the synthetic glucocorticoid dexamethasone, and suggest that specific interactions occur between lymphokines and naturally produced glucocorticoids in vivo, which may play a role in the regulation of the immune response.

Cell Death↗
PubMed1992

Mls-1 is encoded by the long terminal repeat open reading frame of the mouse mammary tumor provirus Mtv-7.

The murine Mls-1 antigen is the prototype of endogenous superantigens, molecules whose activities lead to deletion of T cells expressing certain T-cell receptor V beta genes from the mature repertoire. However, Mls-1 also stimulates T cells expressing these particular V beta genes (V beta 6, V beta 7, V beta 8.1, and V beta 9) in vitro, making it one of the strongest known T-cell activators. We have recently reported that the Mls-1 gene is closely linked to the endogenous mammary tumor virus Mtv-7. We now demonstrate that Mls-1 is encoded by the open reading frame in the U3 region of the long terminal repeat of Mtv-7. However, control of expression of this molecule seems complex, depending on the promoter used for the transfection experiments. The sequence of the Mtv-7 open reading frame differs from all other known mammary tumor virus open reading frame sequences in the 3' end, suggesting that the T-cell receptor V beta specificity is conferred by the C terminus of the molecule. The predicted structure of the protein encoded by the open reading frame is consistent with a type II transmembrane molecule where the C terminus is extracellular.

Amino Acid Sequence↗
PubMed1992

Mls-1-like superantigen in the MA/MyJ mouse is encoded by a new mammary tumor provirus that is distinct from Mtv-7.

Mls-1 is an endogenous superantigen that leads to in vivo deletion and in vitro stimulation of T cell receptor (TCR) V beta 6-, 7-, 8.1-, and 9-expressing cells. The MA/MyJ mouse deletes the identical set of TCR from its mature T cell repertoire; however, it does not contain Mtv-7, the murine mammary tumor provirus (MMTV), whose sag gene encodes Mls-1. Interestingly, the superantigen activity of this mouse strain segregates with a new mammary tumor provirus, Mtv-43, not seen in other inbred strains. The predicted amino acid sequence of the sag gene of Mtv-43 was compared with that of Mtv-7. Strikingly, the COOH terminus of the two molecules is very similar, while all other MMTV-encoded superantigens differ 100% in this segment.

Aging↗
PubMed1992

Interleukin-1 induces protein tyrosine phosphorylation in T cells.

Interleukin (IL)-1 alpha activates multiple signal transmission pathways in the T helper type 2 cell line, D10A, and these pathways are linked to two separate IL-1 receptors (IL-1R). In the present report we show that IL-1 induces the activation of tyrosine kinase in these cells, leading to tyrosine phosphorylation of a subset of proteins of 38, 75, 97 and 115 kDa. This type of phosphorylation is prevented by a monoclonal antibody directed against the 80-kDa IL-1R and by tyrphostins which are specific inhibitors of tyrosine kinases. In addition, this inhibitor blocks IL-1-and IL-2-induced proliferation in D10A cells as well as the c-myc and c-myb proto-oncogene mRNA expression in response to IL-1. Interestingly, the inhibitor of cAMP-dependent kinase, H-8, only blocks IL-1-induced c-myb, but not c-myc mRNA expression. Altogether, our results demonstrate that the activation of a tyrosine kinase(s) is an early and major event that happens after IL-1/IL-1R interaction, leading to an increase in intracellular cAMP which results in c-myb and IL-5 mRNA expression. Independent of cAMP, by tyrosine phosphorylation of specific substrates IL-1 also induces c-myc and IL-6 mRNA expression and cellular proliferation.

Animals↗
PubMed1992

Interleukin-1 induces c-fos and c-jun gene expression in T helper type II cells through different signal transmission pathways.

Interleukin (IL)-1 induces proliferation and expression of several protooncogenes in the T helper 2 cell line D10A. We have analyzed the signal transmission pathways activated by IL-1 in these cells, leading to the expression of c-jun and c-fos. IL-1 induced c-jun gene transcription and mRNA expression by means of a pathway dependent on protein tyrosine kinase activity since tyrphostin, a specific inhibitor of tyrosine kinase, inhibited this induction. This mechanism of transmission signaling was independent of protein kinase C (PKC) and was linked to the 80-kDa IL-1 receptor (IL-1R). In addition, phorbol esters did not induce c-jun mRNA expression, whereas c-fos mRNA expression mediated by IL-1 dependent on PKC; this pathway was linked to a different, still unidentified IL-1R that was functional in the D10A cell line. Accumulation of intracellular cAMP generated by IL-1 through the 80-kDa IL-1R negatively regulated c-fos expression which was induced by IL-1 through PKC activation. We conclude that IL-1 modulates the expression of c-fos in D10A cells by occupying of two independent IL-1R that are linked to different signal transduction pathways.

Cyclic AMP↗
PubMed1992

Mls genes and self-superantigens.

The Mls gene products, which have long been known for their potent T-cell stimulatory function, have recently come of age through two pivotal discoveries, revealing that they act as superantigens and originate from retroviruses. In addition, recent experiments suggest that two retroviruses, the murine B-type mammary tumor virus and the human lentivirus HIV, make use of the T-cell stimulatory capacity of a virally encoded superantigen for facilitating viral replication.

Amino Acid Sequence↗
PubMed1992

Molecular characterization of Mls-1.

Recently a series of endogenous and exogenous superantigens have been described which have one common feature, namely, they lead to in vivo deletion and in vitro stimulation of T cells expressing particular T cell receptor V beta genes. The Mls antigens represent the prototypes of these molecules. We have mapped Mls-1 to the endogenous mammary tumor virus (MMTV) Mtv-7, while other SAG have also been associated with various MMTV. The open reading frame gene of the MMTV encodes the SAG. Thus, the new terminology MMTV sag has been proposed for this gene. Transfection experiments suggest that the expression of MMTV sag is tightly controlled, probably by a negative acting factor encoded within the open reading frame. Furthermore, a pronounced IL-4 effect is seen in the functional detection of the transfected Mtv-7 sag. Since this lymphokine does not influence the mRNA level of the endogenous or transfected MMTV genes, it is likely that it exerts its effect by increasing transcription of MHC class II genes, whose products are required for functional detection of Mls. We have identified one mouse strain, MA/MyJ, which has an Mls-1 phenotype but does not contain Mtv-7. The SAG activity of this strain was mapped to a new mammary tumor provirus, Mtv-43, not seen in other inbred strains. Sequence analyses revealed that the predicted amino acid sequences of the Mtv-7 and the Mtv-43 sag genes are very similar. This is particularly striking in the C-terminus, where all other MMTV sag sequences differ 100%. Thus, this region of the molecule seems to control the V beta specificity of SAG molecules. It is likely that the SAG expression provides an advantage for the infectious MMTV, probably by facilitating its transmission by T cells from the site of primary residence in the gut to its final destination, the mammary glands.

Amino Acid Sequence↗
PubMed1992

Mls superantigens: how retroviruses influence the expressed T cell receptor repertoire.

The murine Mls antigens were originally discovered because they have an enormous T cell stimulatory capacity, exceeding in strength any other antigen. The finding that Mls interacts directly with the V beta segment of the T cell receptor, leading to in vivo deletion and in vitro stimulation of T cells expressing particular V beta genes, provided an explanation for this phenomenon and led to the formulation of the new term of superantigen. Recently it was discovered by several groups that these superantigens are encoded by type B retroviruses, the mammary tumor viruses which are transmitted vertically as infectious particles or exist as proviruses in the murine genome.

Amino Acid Sequence↗