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Biomedical subjects

A Sette

Publications and source records attributed to A Sette.

At least 271 records · Page 15Linked to original sources
PubMed1989

Relative contribution of "determinant selection" and "holes in the T-cell repertoire" to T-cell responses.

Using BALB/c and CBA/J mice, the I-region associated (Ia) binding capacity and T-cell immunogenicity of a panel of 14 overlapping peptides that span the entire sequence of the protein staphylococcal nuclease (Nase) was examined to evaluate major histocompatibility gene complex (MHC) control of T-cell responses. Ia binding and Ia-restricted T-cell immunogenicity could be determined for a total of 54 peptide-MHC combinations. Only 30% of the 54 instances examined involved detectable Ia binding, but they represented almost all (12 of 13) of the immune responses found. However, binding to Ia was not sufficient to ensure T-cell immunogenicity, since only 70% of the binding events were productive--i.e., were associated with an immune response. Thus, Ia molecules have the expected characteristics of a highly permissive capacity for antigen interaction that allows them to function as restriction elements for a large universe of antigens. On the other hand, since the Ia molecules cannot distinguish between self and non-self, not all antigen-Ia interactions would be permitted to elicit a T-cell response. It appears that both Ia binding ("determinant selection") and T-cell repertoire act in concert to define the immune response status of an individual toward any particular T-cell epitope.

Animals↗
PubMed1989

Prediction of major histocompatibility complex binding regions of protein antigens by sequence pattern analysis.

We have previously experimentally analyzed the structural requirements for interaction between peptide antigens and mouse major histocompatibility complex (MHC) molecules of the d haplotype. We describe here two procedures devised to predict specifically the capacity of peptide molecules to interact with these MHC class II molecules (IAd and IEd). The accuracy of these procedures has been tested on a large panel of synthetic peptides of eukaryotic, prokaryotic, and viral origin, and also on a set of overlapping peptides encompassing the entire staphylococcal nuclease molecule. For both sets of peptides, IAd and IEd binding was successfully predicted in approximately 75% of the cases. This suggests that definition of such sequence "motifs" could be of general use in predicting potentially immunogenic peptide regions within proteins.

Amino Acid Sequence↗
PubMed1988

Autologous peptides constitutively occupy the antigen binding site on Ia.

Low molecular weight material associated with affinity-purified class II major histocompatibility complex (MHC) molecules of mouse (Ia) had the expected properties of peptides bound to the antigen binding site of Ia. Thus, the low molecular weight material derived from the I-Ad isotype was efficient in inhibiting the binding of 125I-labeled I-Ad-specific peptide to I-Ad, but did not significantly inhibit the binding of an I-Ed-specific peptide to I-Ed; the reciprocal isotype-specific inhibition was demonstrated with low molecular weight material derived from I-Ed. The inhibitory material was predominantly peptide in nature, as shown by its susceptibility to protease digestion. It was heterogeneous as measured by gel filtration (mean molecular weight approximately 3000), and when characterized by high-performance liquid chromatography, it eluted over a wide concentration of solvent. Such self peptide-MHC complexes may have broad significance in the biology of T cell responses, including generation of the T cell repertoire, the specificity of mixed lymphocyte responses, and the immune surveillance of self and nonself antigens in peripheral lymphoid tissues.

Animals↗
PubMed1988

I-Ad-binding peptides derived from unrelated protein antigens share a common structural motif.

Purified Ia molecules can specifically bind many unrelated peptide Ag, and such binding appears to be a necessary, albeit not sufficient, prerequisite for the immunogenicity of the proteins from which such peptides are derived. We have recently analyzed the affect of single amino acid substitutions on the I-Ad binding of the immunogenic peptide OVA 323-339. The results obtained demonstrated the very permissive nature of Ag-Ia interaction. We also showed that unrelated peptides that are good I-Ad binders share a common structural motif and speculated that recognition of such motifs could represent a mechanism to achieve a very permissive type of interaction that yet retained some degree of specificity. In the present set of experiments we analyzed the I-Ad binding pattern of a series of overlapping peptides derived from sperm whale myoglobin (residues 102-125) and influenza hemagglutinin (residues 121-146) to determine whether the peptide regions predicted on the basis of structural similarity to be involved in I-Ad binding were in fact involved. In both cases, the I-Ad-interacting determinants were found to contain the sequence motif postulated to be important for I-Ad binding. These data support the hypothesis that I-Ad molecules recognize a large library of Ag by virtue of common structural motifs present in peptides derived from phylogenetically unrelated proteins.

Amino Acid Sequence↗
PubMed1988

Interaction of an immunodominant epitope with Ia molecules in T-cell activation.

The amino acid sequence corresponding to residues 107-116 of hen egg-white lysozyme (HEL) has been identified as containing an immunodominant T-cell epitope recognized in association with the I-Ed molecule. The immunodominance of this epitope in HEL-primed H-2d mice was demonstrated by analysis of the T-cell proliferative response induced by synthetic peptides covering almost the entire HEL sequence. All the T-cell hybridomas from H-2d mice analyzed recognize the HEL sequence 107-116 in association with the I-Ed molecule. Correlating with the restriction of T-cell recognition, HEL-(105-120)-peptide binds to I-Ed but not to I-Ad molecules. Conservative or semiconservative substitutions at positions 113 (Asn----Lys), 114 (Arg----His), or 115 (Cys----Ala) abrogate the ability of HEL-(105-120) to activate T cells. Substitutions at residues 113 and 115 affect T-cell recognition but not the binding to I-Ed molecules, whereas, as shown by binding data and competition experiments, an Arg----His substitution at position 114 profoundly impairs the capacity of the peptide to interact with I-Ed molecules. In agreement with these results, [Lys113]HEL-(105-120)-peptide but not [His114]HEL-(105-120)-peptide was found to be immunogenic in H-2d mice. Thus, a single semiconservative substitution drastically reduces binding capacity and abolishes immunogenicity, suggesting that a strict correlation exists between binding of a peptide to Ia molecules and its immunogenicity.

Amino Acid Sequence↗
PubMed1988

Facts on the fragmentation of antigens in presenting cells, on the association of antigen fragments with MHC molecules in cell-free systems, and speculation on the cell biology of antigen processing.

The processing of a protein antigen is a multi-step event taking place in antigen-presenting cells. Processing is a prerequisite for the recognition of most antigens by T lymphocytes. The antigen is ingested by endocytosis, transported to an acid cellular compartment and subjected to proteolytic fragmentation. Some of the antigen fragments bind to MHC class II molecules and are transported to the surface of the antigen-presenting cell where the actual presentation to T lymphocytes occurs. The nature of the processed antigen, how and where it is derived and subsequently becomes associated with MHC molecules are the questions discussed in this review. To us, the entire concept of processing has appeal not only because it explains some hitherto well-established, but poorly understood, phenomena such as the fact that T lymphocytes focus their attention entirely upon antigens on other cells. It has appeal also because processing allows for a thorough scrutiny of all the proteins of a cell including both the proteins which have been taken up from the environment (mostly MHC class II-restricted) and the cell's own proteins (mostly MHC class I-restricted). Through the mechanism of processing fragments of all these proteins including "internal" fragments which are not present on the globular protein's surface are brought out on the cell surface in association with MHC molecules and displayed to the T-lymphocyte system. This allows for the identification and, if necessary, the destruction of cells which in their interior harbor abnormal proteins, be they derived from virus-encoded genes or other abnormal genes.

Antigen-Antibody Complex↗
PubMed1987

The relation between major histocompatibility complex (MHC) restriction and the capacity of Ia to bind immunogenic peptides.

The capacity of purified I-Ad, I-Ed, I-Ak, and I-Ek to bind to protein derived peptides that have been previously reported to be T cell immunogens has been examined. For each of the 12 peptides studied strong binding to the relevant Ia restriction element was observed. All the peptides bound more than one Ia molecule; however, for 11 of 12 peptides, the dominant binding was to the restriction element, whereas in one instance the dominant binding was to a nonrestriction element. When the peptides were used to inhibit the presentation of antigen by prefixed accessory cells to T cells, an excellent correlation was found between the capacity of a peptide to inhibit the binding of an antigen to purified Ia and the capacity of the peptide to inhibit accessory cell presentation of the antigen. Thus, the binding of peptide to purified Ia is immunologically relevant, and Ia seems to be the only saturable molecule on the surface of the accessory cell involved in antigen presentation. Inhibition analysis also indicated that all peptides restricted to a particular Ia molecule competitively inhibited one another, suggesting that each Ia restriction element has a single binding site for antigen. Cross-linking of labeled peptides to Ia followed by electrophoretic analysis and autoradiography suggested that this single binding site is made up of portions of both alpha and beta chains of Ia.

Animals↗
PubMed1987

Immunological self, nonself discrimination.

The ability of immunodominant peptides derived from several antigen systems to compete with each other for T cell activation was studied. Only peptides restricted by a given transplantation antigen are mutually competitive. There is a correlation between haplotype restriction, ability to bind to the appropriate transplantation antigen, and ability to inhibit activation of other T cells restricted by the same transplantation antigen. An exception was noted in that a peptide derived from an antigen, bacteriophage lambda cI repressor, binds to the I-Ed molecule in a specific way, yet is not I-Ed-restricted. Comparison of the sequence of the repressor peptide with that of other peptides able to bind to (and be restricted by) I-Ed and a polymorphic region of the I-Ed molecule itself revealed a significant degree of homology. Thus, peptides restricted by a given class II molecule appear to be homologous to a portion of the class II molecule itself. The repressor-derived peptide is identical at several polymorphic residues at this site, and this may account for the failure of I-Ed to act as a restriction element. Comparison of antigenic peptide sequences with transplantation antigen sequences suggests a model that provides a basis for explaining self, nonself discrimination as well as alloreactivity.

Animals↗
PubMed1986

Isolation and characterization of antigen-Ia complexes involved in T cell recognition.

Using equilibrium dialysis, it has been previously demonstrated that immunogenic peptides bind specifically to the Ia molecules serving as restriction elements in the immune response to these antigens. Using gel filtration to study the formation of ovalbumin (OVA) peptide-I-Ad complexes, it is herein demonstrated that the complexes, once formed, are very stable (kd approximately equal to 3 X 10(-6) s-1), but the rate of complex formation is very slow (ka approximately 1 M-1 s-1 explaining the overall low equilibrium constant of approximately 2 X 10(-6) M. Treating the complexes with glutaraldehyde revealed that the ovalbumin peptide was cross-linked solely to the alpha chain of I-Ad. Planar membranes containing I-Ad-OVA complexes stimulated a T cell response with 2 X 10(4) less antigen than required when uncomplexed antigen was used, thus demonstrating the biologic importance of these complexes in antigen recognition.

Antigens↗
PubMed1986

A microcomputer program for probit analysis of interleukin-2 (IL-2) titration data.

IL-2 activity is commonly estimated in cell culture supernatants by an IL-2-dependent cell proliferation assay. This method is both reproducible and sensitive. However, it often appears from the literature that statistical analysis of the titration data either is disregarded or, when performed, is based on statistically incorrect assumptions. The proposed method is based on the principle of biological assay by parallel lines as applied to probit analysis of quantitative responses. The procedure has been embodied in a simple and interactive computer program which automatically estimates the IL-2 concentration in the biological sample, in terms of U/ml, and provides its standard error and confidence limits. This program is also suitable for quantitative determination of other biologically active substances that show a sigmoid dose/response relationship.

Animals↗
PubMed1986

Analysis of lysozyme-specific immune responses by synthetic peptides. I. Characterization of antibody and T cell-mediated responses to the N-terminal peptide of hen egg-white lysozyme.

The immunological reactivity against the N-terminal region of hen egg-white lysozyme (HEL) has been investigated by a synthetic peptide (PHEL) comprising residue 1-18 of HEL and by an analogue peptide (PREL) in which phenylalanine at position 3 is substituted by tyrosine. Both peptides are immunogenic in (C57BL/10 X DBA/2)F1 mice genetically responder to HEL. In C57BL/6 mice, genetically nonresponder to HEL, PREL induces anti-peptide antibodies that also bind to PHEL whereas PHEL is not immunogenic. Thus, a single amino acid substitution in a synthetic peptide converts a nonresponder mouse strain into a responder one. Anti-PHEL antibodies demonstrate a higher binding to HEL than anti-PREL antibodies, indicating that phenylalanine at position 3 is important for induction of anti-peptide antibodies able to recognize native HEL. At the T cell level the two peptides show very high bidirectional cross-reactivity between themselves and with HEL for interleukin 2 production, antigen-specific proliferation and delayed-type hypersensitivity response, whereas conservation of phenylalanine at position 3 is required for induction of suppressor cells cross-reactive with HEL. This indicates that the N-terminal region of HEL contains epitope(s) able to induce the same level of helper T cell activity as the native HEL molecule. However, helper T cells do not discriminate between PHEL and PREL whereas phenylalanine at position 3 is critical for HEL-specific suppressor T cell induction.

Animals↗
PubMed1986

A microcomputer program for hydrophilicity and amphipathicity analysis of protein antigens.

A simple and ready-to-use program to analyze hydrophilicity and amphipathicity characteristics of protein sequences is described. Three of the most commonly used hydrophilicity scales can be selected and the block length can also be varied. The program is written in BASIC language, can be run on any microcomputer and does not require computer experience. The program output is exemplified by a sample of lysozyme hydrophilicity and amphipathicity analysis.

Computers↗