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P Portoles

Publications and source records attributed to P Portoles.

8 recordsLinked to original sources
PubMed1992

Autoreactivity of low but not of high CD4 variants of an antigen-specific, I-A-restricted mouse T cell clone.

Variant lines expressing high and low surface densities of the accessory molecule CD4 have been developed by repeated preparative flow cytometric cell sortings from the murine Th cell clone D10.G4.1 (D10). The high CD4 variant line (D10H) fully maintained the original I-Ak restricted specificity for conalbumin of wild-type D10 cells. In contrast, the low CD4 variant line (D10L) showed a strong autoreactivity to I-Ak carrying stimulator cells alone which was only slightly augmented by addition of conalbumin. Cell surface molecules other than CD4, including TCR, CD3, CD11a, CD2, CD45, CD44, and MHC class I, remained identical on D10H and D10L sublines as on D10 wild-type cells. The possibility that D10L cells had suffered alterations of their TCR-alpha beta was excluded by demonstrating their reactivity with a panel of eight different anti-clonotypic mAb specific for various epitopes of the D10 TCR. By limiting dilution analysis we show that the majority of responding cells of D10L sublines were autoreactive. Although the reactivity for allogeneic I-A also increased as compared with D10H cells, a clear preference for self-I-Ak was maintained so that a true autoreactive phenotype was evident. The results indicate that the surface concentration of CD4 has a decisive influence on self-non-self discrimination of MHC class II-restricted Th cells.

Animals↗
PubMed1989

Monoclonal antibodies to murine CD3 epsilon define distinct epitopes, one of which may interact with CD4 during T cell activation.

The TCR is comprised of two variable chains that confer specificity, called alpha:beta or gamma:delta, physically associated with five different molecules that comprise the complex known as CD3. Antibodies to this complex are very useful, as they react with all T lymphocytes. A rat mAb to mouse CD3 has been prepared. It reacts with 100% of T cells in all mouse strains tested but with no other cell type. It binds to the CD3 epsilon chain. This antibody activates cloned T cell lines and normal T cells, provided suitable accessory cells and signals are present. This antibody detects a determinant similar to but not identical with those detected by two previously reported hamster anti-CD3 epsilon antibodies. This antibody fixes C efficiently, and it is thus useful for depletion of T cells from bulk populations. Activation of T cells by one of the three different anti-CD3 epsilon antibodies was inhibited by the Fab fragment of anti-CD4, similar to the effects of anti-CD4 Fab on two previously reported anti-TCR V region antibodies that bind a CD3 epsilon-associated epitope. This further defines a site involving TCR V regions and CD3 epsilon with which CD4 appears to associate during T cell activation.

Animals↗
PubMed1989

Inhibition of the responses of a cloned CD4+ T cell line to different class II major histocompatibility complex ligands by anti-CD4 and by anti-receptor Fab fragments are directly related.

The responses of a single cloned T cell line to three different class II major histocompatibility complex (MHC) ligands have been compared for avidity, determined by inhibition with anti-T cell receptor Fab fragments directed at two different receptor epitopes, and for ease of inhibition with anti-CD4 antibody. It has, thus, been directly demonstrated that ease of inhibition of the response of a T cell to a class II MHC ligand by anti-CD4 is inversely related to the avidity of the T cell receptor for that ligand. The difficulties in inferring from this finding that CD4 acts primarily by increasing receptor avidity for its class II MHC ligand are discussed in the light of evidence suggesting that CD4 is an active signaling component of the T cell receptor for class II MHC ligands.

Animals↗
PubMed1989

Cross-linking and conformational change in T-cell receptors: role in activation and in repertoire selection.

TCRs undergo a series of interactions with ligands during development. We have characterized the interaction of a TCR with its ligand and the attendant co-receptor and co-ligand structures. This characterization has led to the model in which the TCR not only binds to class II MHC, but also binds to CD4 co-receptors and co-ligands such as Mls. We have shown that both cross-linking and conformational change in the TCR are required for optimal T-cell activation. Finally, we have used the observation that a particular self-peptide found abundantly associated with class II MHC in the periphery is essentially lacking from thymic cortical epithelium to argue that positive selection for self-MHC recognition may occur by a novel process in the thymic cortex. A TCR recognizing class II MHC with low affinity could either be multiply cross-linked in the absence of conformational change, which here would be driven by a unique peptide, or could be conformationally changed without cross-linking due to the rarity of the individual high-affinity peptide on thymic cortical epithelial cells. Either proposal leads to a partial signal one delivered via the TCR, which we refer to as signal one-half. This signal one-half would induce the cell to repress its other co-receptor molecule and to undergo maturation events such as up-regulation in TCR expression. Such cells are then rigorously screened for activating interactions with autologous structures, such as Mls. The threshold for clonal deletion is set very low to avoid autoreactivity. By this combination of signaling events, a mature TCR repertoire is generated that has the functional characteristics observed in immune systems.

Animals↗
PubMed1989

Asymmetry in the recognition of antigen: self class II MHC and non-self class II MHC molecules by the same T-cell receptor.

One of the most puzzling observations in immunology is the very high frequency of T cells reactive to non-self MHC molecules. Earlier studies from our laboratory suggested that the same receptor on a cloned T-cell line recognized both self-class II MHC: antigen complexes and non-self class II MHC, the latter at a significantly lower affinity. This suggested that alloreactivity resulted from low affinity cross-reactions of the T-cell receptor to a ligand presented at high multiplicity. The present studies address the question of whether these two ligands are recognized symmetrically by this receptor, and of whether different subsites in the receptor recognize both classes of ligands equally. In the present studies, we have greatly extended our analysis of T-cell receptor recognition of antigen: self class II MHC and non-self class II MHC. Using Fab fragments of monoclonal anti-T-cell receptor antibodies as monovalent competitive antagonists of T-cell activation, the response of cloned H-2k T-cell line D10 to conalbumin: I-Ak and to the allogeneic ligands I-Ab,v,p,q was analyzed with monoclonal antibodies directed at 3 clonotypic epitopes and one on V beta. These studies confirmed our earlier finding that D10 activation by antigen: self class II MHC is more difficult to inhibit with clonotypic Fab fragments binding to three distinct clonotypic epitopes than are responses to non-self MHC. More importantly, the Fab fragment of anti-V beta monoclonal antibodies preferentially inhibit activation by antigen: self class II MHC, and do so more efficiently than expected, based on the numbers of molecules of Fab bound.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Immune recognition and effector function in subsets of CD4 T cells.

T cells expressing the cell surface differentiation antigen CD4 are involved in most immune responses. Our studies address two issues about CD4 T cell responses to antigen: first, how does the T cell receptor come together with its ligand to generate an immune response, and what is the role of the CD4 molecule in this response? Second, are all CD4 T cells identical in their functional activity, and how does the activating signal determine the functional outcome of a response? Our studies outlined below suggest that the T cell receptor and its peptide: class II major histocompatibility complex (MHC) molecule ligand come together in a defined orientation determined in part by the binding of CD4 to both the T cell receptor and its ligand. Our studies suggest that the V beta chain is involved directly in MHC antigen recognition, binding self MHC with low affinity and non-self MHC with high affinity. The selective effect of the Mls locus on V beta expression is believed to reflect the binding of the Mls protein directly to the V beta region. CD4 is described as a co-receptor, forming an inducible part of the T cell receptor and binding to the same class II MHC molecule as that receptor. Studies with both cloned lines and normal CD4 T cell populations suggest the existence of two separable subsets with definable function. One set appears to be specialized for the activation of the humoral immune response, while the other drives the cell-mediated immune responses, particularly those involving the activation of macrophages. These two subsets of CD4 T cells have differential activation requirements, seen particularly in the requirement for interleukin 1 (IL-1) in the activation and clonal expansion of CD4 T cells involved in humoral immunity. This requirement for IL-1 may also be observed in the priming of this subset of CD4 T cells. These studies demonstrate that the optimal activation of CD4+ T cells involves recognition of peptide fragments presented by class II MHC molecules and accessory signals derived from the antigen presenting cells.

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