Showing papers by "Mark M. Davis published in 1992"

The presence of interleukin 4 during in vitro priming determines the lymphokine-producing potential of CD4+ T cells from T cell receptor transgenic mice.

Abstract: To study the factors that determine whether CD4+ T cells produce interleukin 4 (IL-4) or interferon gamma (IFN-gamma) upon stimulation we used a system allowing naive T cells to be primed in vitro by specific antigen. Dense CD4+ T cells were purified from mice that expressed transgenes encoding a T cell receptor specific for pigeon cytochrome C peptide 88-104 in association with I-Ek. These T cells produced very limited amounts of IL-4 and IFN-gamma upon immediate challenge with 88-104 and antigen-presenting cells (APC). However, after an initial "priming" culture in which they were incubated for 4 d in the presence of 88-104, APC, and 1,000 U/ml IL-4, the T cells acquired the capacity to produce substantial amounts of IL-4 upon rechallenge but made very little IFN-gamma. Cells primed in the absence of IL-4 produced IFN-gamma upon rechallenge but virtually no IL-4. The inhibitory effect of IL-4 on IFN-gamma production did not appear to be mediated by the induction of IL-10 production since IL-10 addition to initial cultures did not suppress priming for IFN-gamma production, nor did anti-IL-10 block the inhibitory effect of IL-4. IFN-gamma itself did not increase priming for IFN-gamma production, nor did anti-IFN-gamma reduce such priming. IFN-gamma did, however, diminish priming for IL-4 production when limiting amounts of IL-4 (100 U/ml) were used in the initial culture. The dominant effect of IL-4 in determining the lymphokine-producing phenotype of primed cells was observed with dendritic cells (DC), activated B cells, and I-Ek-transfected fibroblasts as APC. However, the different APC did vary in their potency, with DC being superior to activated B cells, which were superior to transfected fibroblasts.

Mapping T-cell receptor-peptide contacts by variant peptide immunization of single-chain transgenics.

Abstract: To test models of T-cell recognition, mice transgenic for T-cell receptor α or β chain have been immunized with variant peptides that force changes in the resulting T-cell response. In particular, charge substitutions on the peptide often elicit reciprocal charges in the junctional (CDR3) sequences of T-cell receptor Vαor Vβ chains, indicating direct T-cell receptor–peptide contact, and allowing derivation of a topology for the T-cell receptor–MHC interaction. At one position on the peptide, variants transformed a homogeneous Vβ response into a very heterogeneous one.

Molecular Components of T-Cell Recognition

Abstract: We review recent data that increase our understanding of the ternary complex of the T cell receptor (TCR), antigenic peptides, and molecules of the major histocompatibility complex (MHC). Studies using synthetic peptide analogs for T-cell antigens have identified peptide residues that appear to interact with the MHC molecule and/or the TCR. The logical extension of these studies, using a complete replacement set of peptide analogues for a model peptide antigen, has more precisely defined the biochemical character of putative MHC and TCR contact residues, and indicated that the TCR is highly sensitive to subtle changes in peptide conformation. Insight into the binding site for peptide on the TCR has recently come from variant peptide immunization of TCR single-chain transgenic mice. These experiments indicate that residues encoded by the V(D)J junctions of both TCR chains contact peptide directly. TCR-MHC contacts have also been studied, using in vitro-mutagenized MHC molecules, particularly those altered at residues predicted to point "up," toward the TCR. These studies reveal that TCR-MHC contacts appear to be quite flexible, and vary between even closely related TCRs. A measure of the affinity of TCR for peptide/MHC complexes has come from competition experiments using soluble MHC complexed with specific peptides. This affinity, with a KD of 5 x 10(-5) M, is several orders of magnitude lower than that of most antibodies for their protein antigens and suggests that the sequence of events leading to T-cell activation begins with antigen-independent adhesion.

pH dependence and exchange of high and low responder peptides binding to a class II MHC molecule.

Abstract: We have compared the binding kinetics of two antigenic peptides to a soluble class II MHC molecule. One of the peptides provokes a strong T cell response and the other a much weaker one. Both show greatly increased (approximately 40-fold) association rates at pH 5 in comparison to neutral pH, consistent with the low pH environment of late endosomes being most conducive to class II MHC--peptide binding. Interestingly, the weak peptide has a much faster off-rate that is significantly increased at pH 5 and it can be entirely replaced in an exchange reaction by the stronger one. This suggests that one characteristic of immunodominant peptides is that of nearly irreversible binding, such that they will be strongly selected for in the course of class II MHC transit and recycling through endosomal compartments. Modelling the parameters of this peptide exchange also suggests that a large fraction of the GPI-chimeric MHC molecules used in this study are 'empty' with respect to endogenous peptides, or else occupied with extremely weak ones, consistent with their inability to load processed peptides intracellularly.

Analysis of a T cell receptor gene as a target of the somatic hypermutation mechanism.

Abstract: In an effort to identify cis-acting elements required for targeting of the somatic hypermutation process in mice, we examined whether a T cell receptor (TCR) transgene under the control of the immunoglobulin (Ig) heavy (H) chain intron enhancer would be mutated in antigen-stimulated B cells. Hybridomas were established from splenic B cells of mice carrying two copies of the TCR transgene after hyperimmunization with phosphorylcholine keyhole limpet hemocyanin. Northern analysis revealed that all of the transgene-containing hybridomas expressed the TCR mRNA. Multiple somatic point mutations were found in seven of eight endogenous Ig VH genes examined. In contrast, 29 of 32 TCR genes examined contained no mutations. One potential mutation was seen in each of the three other TCR genes. Our data indicate that although the TCR transgene is expressed in B cells, it is not efficiently targeted by the mutator mechanism. Furthermore, the presence of an Ig H chain enhancer is itself not sufficient for targeting of the somatic hypermutation mechanism.

Molecular components of

Abstract: We review recent data that increase our understanding of the ternary complex of the T cell receptor (TCR), antigenic peptides, and molecules of the major histocompatibili ty complex (MHC). Studies using synthetic peptide analogs for T-cell antigens have identified peptide residues that appear to interact with the MHC molecule and/or the TCR. The logical extension of

Analysis of a T Cell Receptor Gene as a Target of the Somatic Hypermutation Mechanism By John Hackett, Jr., Chris Stebbins,* Brian Rogerson,~ t

Abstract: Summary In an effort to identify c/s-acting elements required for targeting of the somatic hypermutation process in mice, we examined whether a T cell receptor (TCR) transgene under the control of the immunoglobulin (Ig) heavy (H) chain intron enhancer would be mutated in antigenstimulated B cells. Hybridomas were established from splenic B cells of mice carrying two copies of the TCR transgene after hyperimmunization with phosphorylcholine keyhole limpet hemocyanin. Northern analysis revealed that all of the transgene-containing hybridomas expressed the TCR mRNA. Multiple somatic point mutations were found in seven of eight endogenous Ig VH genes examined. In contrast, 29 of 32 TCR genes examined contained no mutations. One potential mutation was seen in each of the three other TCR genes. Our data indicate that although the TCR transgene is expressed in B cells, it is not efficiently targeted by the mutator mechanism. Furthermore, the presence of an Ig H chain enhancer is itself not sufficient for targeting of the somatic hypermutation mechanism.