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M S Vacchio

Publications and source records attributed to M S Vacchio.

At least 19 recordsLinked to original sources
PubMed1998

A positive role for thymus-derived steroids in formation of the T-cell repertoire.

T cells undergo rigorous selection processes in the thymus that are necessary to prevent T cells with either autoreactive or nonfunctional T-cell receptors (TCRs) from entering the periphery. Although both positive and negative selection depend on TCR-mediated signals, the means by which a thymocyte interprets these signals to result in survival or death is not understood. Glucocorticoids are known to induce thymocyte apoptosis at high concentrations, but at lower concentrations glucocorticoids can antagonize TCR-mediated deletional signals and allow survival of thymocytes and T cell hybridomas. Interestingly, transgenic mice in which the expression of the glucocorticoid receptor has been downmodulated specifically in thymocytes have abnormal thymocyte differentiation, indicating that glucocorticoids play a significant role in T-cell development. Furthermore, we have demonstrated the presence of steroidogenic enzymes in the thymic epithelium and can show that, in vitro, these cells readily synthesize pregnenolone, the first product in the steroidogenic pathway, and deoxycorticosterone. Inhibition of local glucocorticoid biosynthesis in thymi from TCR transgenic mice during fetal thymic organ culture (FTOC) revealed significant alterations in the process of thymocyte selection. These data suggest that glucocorticoids do not simply suppress the immune system but rather are necessary for thymocyte survival and differentiation.

Animals↗
PubMed1998

Multiple mechanisms of peripheral T cell tolerance to the fetal "allograft".

The fetus represents a foreign entity to the maternal immune system, yet this "natural" allograft is not normally rejected. This unique situation provides a physiologic system to evaluate peripheral tolerance in which the maternal immune system is challenged with relatively rare Ags not previously encountered in the thymus. Using H-Y-specific TCR transgenic mice, we demonstrate that T cells specific for fetal Ags decrease in an Ag-specific manner during pregnancy and remain low postpartum, the result of an encounter with fetal cells expressing the appropriate MHC/peptide complexes. The finding that placental trophoblasts can induce Fas-mediated death of T cells is consistent with peripheral clonal deletion as one mechanism of tolerance. The remaining clonotypic T cells are unresponsive to antigenic stimulation, although neither TCR nor coreceptor is down-regulated. Our study demonstrates that specific recognition of fetal allogeneic Ags by maternal T cells results in tolerance induction of reactive T cells via multiple mechanisms.

Animals↗
PubMed1997

Thymus-derived glucocorticoids regulate antigen-specific positive selection.

While it is generally believed that the avidity of the T cell antigen receptor (TCR) for self antigen/major histocompatibility complex (MHC) determines a thymocyte's fate, how the cell discriminates between a stimulus that causes positive selection (survival) and one that causes negative selection (death) is unknown. We have previously demonstrated that glucocorticoids are produced in the thymus, and that they antagonize deletion caused by TCR cross-linking. To examine the role of glucocorticoids during MHC-dependent selection, we examined thymocyte development in organ cultures in which corticosteroid biosynthesis was inhibited. Inhibition of glucocorticoid production in thymi from alpha/beta-TCR transgenic mice resulted in the antigen- and MHC-specific loss of thymocytes that normally recognize self antigen/MHC with sufficient avidity to result in positive selection. Furthermore, inhibition of glucocorticoid production caused an increase in apoptosis only in CD+CD8(+) thymocytes bearing transgenic TCRs that recognized self antigen/MHC. These results indicate that the balance of TCR and glucocorticoid receptor signaling influences the antigen-specific thymocyte development by allowing cells with low-to-moderate avidity for self antigen/MHC to survive.

Animals↗
PubMed1997

Activation of the Lck tyrosine kinase targets cell surface T cell antigen receptors for lysosomal degradation.

The mechanism by which TCR expression is regulated was explored by expressing a constitutively active form of the tyrosine kinase Lck (Lck505F) in T cells. Expression of Lck505F down-regulated TCR levels, an effect that was even more pronounced in CD45- T cells, in which the activity of this tyrosine kinase is further enhanced. Cells expressing Lck505F synthesized all TCR subunits, but lysosomal degradation of assembled receptors was enhanced. TCRs were rapidly internalized and degraded after removal of a tyrosine kinase inhibitor that had permitted cell surface expression. Finally, TCR levels on thymocytes were increased by an Lck inhibitor, and activation- but not phorbol ester-induced internalization of TCRs on Jurkat cells was prevented by inhibition or loss of Lck. These studies identify a regulated nonreceptor tyrosine kinase-mediated pathway for targeting cell surface receptors for lysosomal degradation.

Animals↗
PubMed1996

Cross-talk between the T cell antigen receptor and the glucocorticoid receptor regulates thymocyte development.

The fate of an immature thymocyte, life or death, is largely determined by the ligand-specificity of its T cell antigen receptor (TCR). The default pathway for thymocytes bearing TCRs with subthreshold avidity for self-antigens is death (death by neglect). Thymocytes bearing TCRs with high avidity for self also undergo apoptosis (negative selection). Those thymocytes with intermediate avidities, or that perhaps recognize self-peptides that have partial agonist or antagonist properties, survive and differentiate into mature immunocompetent T cells (positive selection). How TCR avidity is interpreted as a "rescue" signal or a death signal is unknown. Based upon a T cell hybridoma model, our laboratory proposed that glucocorticoids, which themselves are potent inducers of thymocyte apoptosis, antagonize TCR-mediated thymocyte deletion and allow positive selection to occur. In fact, epithelial cells in the thymus proved to be a source of steroid production, and interference with steroid synthesis in fetal thymic organ culture resulted in a greatly enhanced sensitivity of thymocytes to TCR-mediated apoptosis. Transgenic mice with reduced glucocorticoid receptor (GR) levels were produced by tissue-specific expression of GR antisense. Thymocytes in these mice had high levels of spontaneous apoptosis, and were exquisitely sensitive to deletion induced by cross-linking the TCR. Moreover, there was a very large (> or = 90%) loss of CD4+CD8+ thymocytes, signifying a block at the CD4-CD8- to CD4+CD8+ transition, perhaps due to apoptosis of cells upon engagement of the pre-TCR in the absence of an antagonizing glucocorticoid stimulus. The molecular mechanism of the antagonism is currently being investigated. These data indicate that there is cross-talk in thymocytes between the TCR and glucocorticoid signaling pathways resulting in apoptosis, and that locally produced steroids, in a paracrine fashion, participate in setting the TCR avidity thresholds that determine whether developing thymocytes survive or die, and therefore help to mold the antigen-specific T cell repertoire.

Animals↗
PubMed1996

Regulation of thymocyte development by glucocorticoids.

It is generally believed that the avidity of the T cell receptor for self antigen/MHC determines the fate of a thymocyte. However, it is not understood how the thymocyte distinguishes a survival signal (positive selection) from a death signal (negative selection). Recent studies from our laboratory have explored the role that thymus-produced glucocorticoids may play in influencing thymocyte development. It appears that glucocorticoids are important and necessary at several points during thymocyte differentiation and that they may regulate antigen-specific T cell development.

Animals↗
PubMed1995

Retinoic acid inhibition of ex vivo human immunodeficiency virus-associated apoptosis of peripheral blood cells.

T cells from human immunodeficiency virus (HIV)-infected individuals undergo spontaneous and activation-induced ex vivo apoptosis. Here we report that peripheral blood mononuclear cells (PBMCs) obtained from six HIV-infected individuals exhibited reduced ex vivo DNA fragmentation and cell death after ingestion of all-trans-retinoic acid (tRA). These effects were attenuated with continued daily RA administration, which correlated with a > 5-fold decrease in serum peak RA concentrations. Incubation of PBMCs from HIV+ individuals with tRA in vitro resulted in decreased DNA fragmentation in a subset of patients, especially those having < 500 CD4+ T cells per mm3. tRA also inhibited apoptosis of preactivated normal PBMCs induced to die by restimulation, which raises the possibility of a common mechanism between activation-induced apoptosis of activated normal PBMCs and apoptosis associated with HIV infection. Whether HIV-associated apoptosis of PBMCs, and its prevention by RA, has an impact on T-cell survival or the course of disease in patients infected with HIV will require further evaluation.

Administration, Oral↗
PubMed1995

A targeted glucocorticoid receptor antisense transgene increases thymocyte apoptosis and alters thymocyte development.

The exquisite sensitivity of thymocytes to steroid-induced apoptosis, the steroidogenic potential of thymic epithelial cells, and the ability of steroid synthesis inhibitors to enhance antigen-specific deletion of thymocytes in fetal thymic organ cultures suggest a role for glucocorticoids in thymocyte development. To address this further, transgenic mice that express antisense transcripts to the glucocorticoid receptor (GR) specifically in immature thymocytes were generated. The consequent hyporesponsiveness of thymocytes to glucocorticoids was accompanied by a reduction in thymic size, primarily owing to a decrease in the number of CD4+CD8+ cells. While an enhanced susceptibility to T cell receptor (TCR)-mediated apoptosis appeared to be partially responsible for this reduction, thymocyte loss could also be detected before thymocytes progressed to the CD4+CD8+ TCR alpha beta-expressing stage. These results suggest that glucocorticoids are necessary for survival and maturation of thymocytes, and are consistent with a role for steroids in both the transition from CD4-CD8- to CD4+CD8+ cells and the survival of CD4+CD8+ cells stimulated via the TCR.

Animals↗
PubMed1994

Steroid production in the thymus: implications for thymocyte selection.

The mouse thymus was assessed for its ability to produce steroids. Cultured thymic non-T cells produced soluble pregnenolone and deoxycorticosterone, and immunohistochemistry demonstrated steroidogenic enzymes in radioresistant thymic epithelial cells but not in thymocytes. Inhibition of thymic corticosterone production or blockade of the glucocorticoid receptor with RU-486 resulted in enhanced TCR-mediated, antigen-specific deletion of immature thymocytes. These data indicate that locally produced glucocorticoids, because of their antagonism of TCR-mediated signaling for death, may be a key element of antigen-specific thymocyte selection.

Aging↗
PubMed1994

Immune responses against self-TCR peptides.

Vaccination of rats against the TCR peptide V beta 8.2 (39-59) was reported to inhibit the immunopathogenic process of EAE. Analysis of the immune response to this peptide and several related TCR peptides yielded the following findings: (i) Lewis rats immunized in vivo and challenged in vitro responded with vigorous lymphocyte proliferative responses to peptide V beta 8.2 (39-59) and to three other rat TCR peptides, V beta 8.3 (15-32), V beta 8.3 (39-59), and V beta 14 (39-59). On the other hand, two other rat peptides, V beta 8.2 (18-38) and V beta 8.3 (62-76), were poorly immunogenic. (ii) Rat peptide V beta 8.2 (39-59) was found more immunogenic than its mouse homolog, in both Lewis rats and B10.A mice. A moderate level of cross-reactivity was observed between these two peptide homologs. (iii) Rats of different genetic makeups varied in their response to peptide V beta 8.2 (39-59). A similar pattern of response of the different rats was found with another TCR peptide, V beta 14 (39-59). Hybrids between high and low responder rat strains resembled the high responders in their response to the TCR peptides. (iv) Sensitized lymph node cells as well as lymphocytes of a cell line specific for peptide V beta 8.2 (39-59) failed to respond to T cells that express the V beta 8.2 gene product. This observation is interpreted to indicate that peptide V beta 8.2 (39-59) is a cryptic determinant of the V beta 8.2 protein. Moreover, the data suggest that lymphocytes proliferating against peptide V beta 8.2 (39-59) may not be responsible for the reported inhibition of EAE in rats vaccinated with this peptide.

Amino Acid Sequence↗
PubMed1994

To be or not to be: mutually antagonistic death signals regulate thymocyte apoptosis.

Recognition of self-antigens by immature thymocytes results in either activation-induced apoptosis (negative selection) or survival (positive selection). While it is believed that T cell receptor avidity plays a role in determining the outcome, the mechanisms responsible for this life or death decision are not known. Recent data concerning the mutual antagonism between activation- and glucocorticoid-induced apoptosis have prompted an examination of the potential interaction of these two signaling pathways in the regulation of antigen-specific selection.

Animals↗
PubMed1993

Preferential V beta usage by cytotoxic T cells cross-reactive between two epitopes of HIV-1 gp160 and degenerate in class I MHC restriction.

The T cell response to HIV-1 gp160 is among the most thoroughly studied immune responses to HIV-1 products. In our previous work, the MHC class I molecule Dd as well as H-2u, p, and q, were found to present P18 and HP53, two determinants of HIV-1 gp160, to CD8+ CTL in mice. We have studied the TCR V beta chain expression in CTL lines, either cross-reactive for these two peptides or specific for P18 alone, in these four different MHC haplotypes. The usage of V beta in T cells showing cross-reaction between these two peptides was remarkably conserved (primarily V beta 8 family, with some use of V beta 14) despite the extensive TCR V beta diversity of the non-cross-reactive CTL, which did not use V beta 8 or 14. This correlation of V beta usage with fine specificity was consistent in H-2d, u, and p (p < 0.01), but not in H-2q. The correlation of V beta use with peptide fine specificity independent of MHC restriction was unexpected. The strong predominance of V beta 8 family TCR was all the more surprising in view of the finding that mice bearing a genomic deletion of V beta 8 can still produce T cells with the cross-reactive phenotype, implying that other V beta chains can produce this specificity. We therefore asked whether the complexes of P18 with H-2d, p, and u are recognized as identical, and observed the surprising result that H-2d, p, and u cells mutually cross-present the peptides P18 and HP53 to allogeneic CTL lines and individual clones of each of the other haplotypes, whereas none of these cross-present to H-2q CTL, nor do H-2q targets present to CTL of the other haplotypes. This degeneracy of MHC restriction is novel for class I molecules. Moreover, the observed restriction in V beta usage occurs only in the unique set of CTL that exhibit both peptide-cross-reactive fine specificity and MHC allogeneic cross-presentation. The observation that a strain of mice in which the V beta 8 family is genomically deleted can still make CTL of this phenotype using another V beta demonstrates the plasticity of the class I MHC-restricted repertoire when the dominating receptor is not available.

Amino Acid Sequence↗
PubMed1993

T cell receptor V alpha-V beta combinatorial selection in the expressed T cell repertoire.

This study has evaluated whether preferential pairing occurs between TCR alpha- and beta-chains expressing specific V alpha and V beta gene products in the mature peripheral T cell population, as a result of either thymic selection or of structural constraints on chain pairing. The association of specific V alpha products with specific V beta products on individual T cells was found, in multiple instances, to be highly selective. Moreover, patterns of preferential V alpha-V beta association were highly strain-specific and were independently expressed in CD4+ and CD8+ T cell subsets. Although these findings do not exclude the possibility that structural constraints may limit V alpha-V beta pairing in other instances, they indicate that the observed instances of skewed expression are not caused by structural constraints in chain pairing. Rather, they suggest that strain-specific selective events alter the expressed V alpha V beta repertoire as a result of recognition of self or environmental Ag during T cell repertoire selection.

Animals↗
PubMed1993

9-cis-retinoic acid inhibits activation-driven T-cell apoptosis: implications for retinoid X receptor involvement in thymocyte development.

Retinoic acid is a morphogenetic signaling molecule derived from vitamin A and involved in vertebrate development. Two groups of receptors, retinoic acid receptors and retinoid X receptors (RXRs), have been identified. All-trans-retinoic acid is the high-affinity ligand for retinoic acid receptors, and 9-cis-retinoic acid additionally binds RXRs with high affinity. Here we report that although retinoic acid has little inhibitory effect on activation-induced T-cell proliferation, it specifically prevents activation-induced apoptosis of T-cell hybridomas and antigen-specific deletion of immature CD4+CD8+ thymocytes from alpha beta T-cell receptor transgenic mice. 9-cis-Retinoic acid was approximately 10-fold more potent than all-trans-retinoic acid, suggesting that RXRs participate in this process. Thus, although 9-cis-retinoic acid has little immuno-suppressive activity, it is a potent negative regulator of activation-induced T-cell apoptosis, raising the possibility that RXRs may take part in regulating T-cell development.

Animals↗
PubMed1992

Influence of T cell receptor V alpha expression on Mlsa superantigen-specific T cell responses.

Recognition of conventional foreign antigen by T cells is determined by the expression of multiple variable regions of both alpha and beta chains of the T cell receptor (TCR) alpha/beta heterodimer. In contrast, there exists a class of antigens that appears to interact with the TCR alpha/beta heterodimer through the variable region on the beta chain (V beta), independent of other TCR components, a property that has led to their designation as superantigens. The goal of the present study was to analyze V alpha use in V beta 6+ T cells responsive to the superantigen, Mlaa. Results indicate that while deletion of T cells expressing V beta 6 in Mlsa-expressing mice is essentially complete and therefore appears to occur regardless of V alpha usage, in vitro Mlsa stimulation of T cells from Mlsa-negative mice results in significant skewing of V alpha use among responding V beta 6+ T cells. This indicates that V alpha expression influences recognition of the superantigen, Mlsa by mature peripheral T cells.

Animals↗
PubMed1992

Cross-species transplantation tolerance: rat bone marrow-derived cells can contribute to the ligand for negative selection of mouse T cell receptor V beta in chimeras tolerant to xenogeneic antigens (mouse + rat----mouse).

Mixed xenogeneic bone marrow reconstitution (mouse + rat----mouse) results in stable mixed lymphopoietic chimerism (1-48% rat), long-term survival, and the induction of stable functional donor-specific transplantation tolerance to xenoantigens in vivo. To examine the role of negative selection of potentially xenoreactive T lymphocytes during tolerance induction across a species barrier, mixed xenogeneic chimeras (mouse + rat----mouse) were prepared and analyzed using a mixture of mouse and rat bone marrow cells for relative T cell receptor (TCR)-V beta expression on mouse T cells. In mixed xenogeneic chimeras (B10 mouse + rat----B10 mouse), T cell maturation proceeded normally in the presence of rat bone marrow-derived elements, and functional donor-specific tolerance to rat xenoantigens was present when assessed by mixed lymphocyte reactivity in vitro. V beta 5, which is expressed at high (undeleted) levels in normal B10 mice, was consistently deleted in B10 recipients of Wistar Furth (WF), but not F344 rat bone marrow, whereas the coadministration of either F344 rat or WF rat bone marrow with B10 mouse bone marrow cells resulted in a significant decrease in expression of TCR-V beta 11. Taken together, these data demonstrate for the first time that rat bone marrow-derived cells can contribute in a strain-specific manner to the ligand for negative selection of specific mouse TCR-V beta during tolerance induction across a species barrier.

Animals↗
PubMed1991

A virus-encoded "superantigen" in a retrovirus-induced immunodeficiency syndrome of mice.

The development of an immunodeficiency syndrome of mice caused by a replication-defective murine leukemia virus (MuLV) is paradoxically associated with a rapid activation and proliferation of CD4+ T cells that are dependent on the presence of B cells. The responses of normal spleen cells to B cell lines that express the defective virus indicated that these lines express a cell surface determinant that shares "superantigenic" properties with some microbial antigens and Mls-like self antigens. This antigen elicited a potent proliferative response that was dependent on the presence of CD4+ T cells and was associated with selective expansion of cells bearing V beta 5. This response was markedly inhibited by a monoclonal antibody specific for the MuLV gag-encoded p30 antigen.

Animals↗