Biomedical subjects

Claire N Manzotti

Publications and source records attributed to Claire N Manzotti.

6 recordsLinked to original sources

PubMed2006

Integration of CD28 and CTLA-4 function results in differential responses of T cells to CD80 and CD86.

CD80 and CD86 have the capacity to either stimulate or inhibit T cell responses through their receptors CD28 and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4). Blockade of CD80 and CD86 in autoimmune disease settings has revealed distinct outcomes, yet the differential functions of CD80 and CD86 are still unclear. We have studied the ability of individual ligands to stimulate primary responses in human CD4(+) T cells. Our data reveal both quantitative and qualitative differences between the ligands. Both CD80 and CD86 demonstrated the capacity to costimulate T cell proliferation. However, CD80 committed a greater number of T cells to divide with faster kinetics, consistent with it being a superior ligand for CD28. Once cell division had been initiated, all T cells undergoing cell division expressed CTLA-4, irrespective of whether CD80 or CD86 costimulation was used. However, only in the presence of CD80 was evidence of CTLA-4 engagement and inhibitory function observed. Finally, differences between CD80 and CD86 costimulation extended to the T cell phenotype, in particular the levels of CD40 ligand expression.

Animals↗

PubMed2005

Exocytosis of CTLA-4 is dependent on phospholipase D and ADP ribosylation factor-1 and stimulated during activation of regulatory T cells.

CTLA-4 is an essential protein in the regulation of T cell responses that interacts with two ligands found on the surface of APCs (CD80 and CD86). CTLA-4 is itself poorly expressed on the T cell surface and is predominantly localized to intracellular compartments. We have studied the mechanisms involved in the delivery of CTLA-4 to the cell surface using a model Chinese hamster ovary cell system and compared this with activated and regulatory human T cells. We have shown that expression of CTLA-4 at the plasma membrane (PM) is controlled by exocytosis of CTLA-4-containing vesicles and followed by rapid endocytosis. Using selective inhibitors and dominant negative mutants, we have shown that exocytosis of CTLA-4 is dependent on the activity of the GTPase ADP ribosylation factor-1 and on phospholipase D activity. CTLA-4 was identified in a perinuclear compartment overlapping with the cis-Golgi marker GM-130 but did not colocalize strongly with lysosomal markers such as CD63 and lysosome-associated membrane protein. In regulatory T cells, activation of phospholipase D was sufficient to trigger release of CTLA-4 to the PM but did not inhibit endocytosis. Taken together, these data suggest that CTLA-4 may be stored in a specialized compartment in regulatory T cells that can be triggered rapidly for deployment to the PM in a phospholipase D- and ADP ribosylation factor-1-dependent manner.

ADP-Ribosylation Factor 1↗

PubMed2004

CD86 and CD80 differentially modulate the suppressive function of human regulatory T cells.

Regulatory T cells (Treg) are important in maintaining tolerance to self tissues. As both CD28 and CTLA-4 molecules are implicated in the function of Treg, we investigated the ability of their two natural ligands, CD80 and CD86, to influence the Treg-suppressive capacity. During T cell responses to alloantigens expressed on dendritic cells, we observed that Abs against CD86 potently enhanced suppression by CD4(+)CD25(+) Treg. In contrast, blocking CD80 enhanced proliferative responses by impairing Treg suppression. Intriguingly, the relative expression levels of CD80 and CD86 on dendritic cells are modulated during progression from an immature to a mature state, and this correlates with the ability of Treg to suppress responses. Our data show that CD80 and CD86 have opposing functions through CD28 and CTLA-4 on Treg, an observation that has significant implications for manipulation of immune responses and tolerance in vivo.

Adjuvants, Immunologic↗

PubMed2003

Identification of a secondary zinc-binding site in staphylococcal enterotoxin C2. Implications for superantigen recognition.

The previously determined crystal structure of the superantigen staphylococcal enterotoxin C2 (SEC2) showed binding of a single zinc ion located between the N- and C-terminal domains. Here we present the crystal structure of SEC2 determined to 2.0 A resolution in the presence of additional zinc. The structure revealed the presence of a secondary zinc-binding site close to the major histocompatibility complex (MHC)-binding site of the toxin and some 28 A away from the primary zinc-binding site of the toxin found in previous studies. T cell stimulation assays showed that varying the concentration of zinc ions present affected the activity of the toxin and we observed that high zinc concentrations considerably inhibited T cell responses. This indicates that SEC2 may have multiple modes of interaction with the immune system that are dependent on serum zinc levels. The potential role of the secondary zinc-binding site and that of the primary one in the formation of the TCR.SEC2.MHC complex are considered, and the possibility that zinc may regulate the activity of SEC2 as a toxin facilitating different T cell responses is discussed.

Animals↗

PubMed2003

What's the difference between CD80 and CD86?

CD28 and CD152 have crucial yet opposing functions in T-cell stimulation, in which CD28 promotes but CD152 inhibits T-cell responses. Intriguingly, they share two ligands, CD80 and CD86, but at present there is no clear model for understanding whether a ligand will promote or inhibit responses. Current perceptions are based around the concept that CD86 is the initial co-stimulatory ligand based on its more abundant and earlier expression pattern; CD80 has a role following antigen-presenting-cell activation. We describe an alternative view in which CD80 is the initial ligand, responsible for maintaining aspects of immune tolerance through interactions with CD152. These inhibitory functions can then be over-ridden by the upregulation of CD86 on dendritic cells as a result of inflammatory stimuli, leading to immune activation.

Animals↗

PubMed2002

Inhibition of human T cell proliferation by CTLA-4 utilizes CD80 and requires CD25+ regulatory T cells.

CD28 and CTLA-4 are opposing regulators of T cell activation, triggered by the two ligands CD80 and CD86. How these ligands promote either T cell activation via CD28 or inhibition via CTLA-4 is not understood. Using CD80 and CD86 molecules expressed on transfected cells, we have identified a major difference between these ligands in that CD80 transfectants have the ability to inhibit activation of resting human peripheral blood T cells via interaction with CTLA-4, whereas CD86 transfectants do not. Rather, CTLA-4-CD86 interactions appear to contribute towards T cell proliferation. We also observed that CTLA-4 function is strongly influenced by TCR stimulation, effects being observed only at relatively low levels of TCR stimulation. The kinetics of CD80-CTLA-4 interactions revealed that CTLA-4 inhibition took place within the first 8 h of T cell stimulation, despite there being little measurable CTLA-4 expression on the majority T cells. However, significant amounts of CTLA-4 were observed in the CD25(+) CD4(+) subset of T cells which, when removed from the cultures, accounted for the CTLA-4 inhibition observed. Overall, these data provide evidence that CD80 and CD86 differ in their interactions with CTLA-4 and that CD80 appears to be the preferential inhibitory ligand for CTLA-4 working via a population of CD4(+) CD25(+) CTLA-4(+) regulatory T cells.

Abatacept↗