Activation of T cells by the ragged tail of MHC class II-presented peptides of the measles virus fusion protein.

The efficient and sustained immune response of an antigen requires T cell epitopes, capable of inducing a long lasting T cell memory. To detect T cell epitopes of the measles virus fusion protein (MV-F), the proliferation of lymphocytes from late convalescent donors in response to overlapping pentadecapeptides covering the whole protein sequence was studied. Three major immunodominant regions (F51-70, F121-135 and F211-225) containing promiscuous peptides induce proliferation in peripheral blood lymphocytes in approximately 50% of the donors.

Alteration of a model antigen by Au(III) leads to T cell sensitization to cryptic peptides.

Certain metal ions are known to be potent sensitizers, but the self proteins modified by metal ions and the self peptides recognized by 'metal-specific' T cells are unknown. In humans and mice treatment with gold anti-rheumatic drugs, containing Au(I), may lead to allergic and autoimmune side effects. Human and murine T cells do not react to Au(I), however, but to the reactive metabolite Au(III).

Peptide-specific antibodies indicate species heterogeneity of a 42 kDa high-affinity inositol 1,3,4,5-tetrakisphosphate receptor protein from brain.

The aim of the present study was to identify a high affinity InsP4 receptor in membranes from cerebellum or brain from several species. In samples obtained from sheep, beef, human and rat, a 42 kDa protein represents an Ins(1,3,4,5)P4 receptor, similar to the InsP4 receptor from pig cerebellum, which we have described previously using an InsP4-photoaffinity analogue (Reiser et al., Biochem.

Characterization of a high-affinity Ins-P4 (inositol 1,3,4,5-tetrakisphosphate) receptor from brain by an anti-peptide antiserum.

From a high-affinity Ins-P4 (inositol 1,3,4,5-P4) receptor purified from pig cerebellum, digested with the protease Lys C peptide sequences were obtained. Synthetic peptide-3 (19 amino acid residues) was used to generate an antiserum. Reaction of the affinity-purified antibodies with the purified pig receptor protein in ELISA or Western blot was completely inhibited by peptide-3.

Relative roles of natural killer- and T cell-mediated anti-leukemia effects in chronic myelogenous leukemia patients treated with interferon-alpha.

Potential anti-leukemia effects mediated by T cells or by natural killer (NK) cells were investigated in chronic myelogenous leukemia (CML) patients treated with interferon-alpha. Therapy-associated modulation of T cell and NK reactivity was monitored for one year from initiation in autologous mixed lymphocyte-tumor cell reactions and cytotoxicity directed against autologous CML cells, respectively. During the course of IFN-therapy, NK activity against autologous CML cells increased steadily, whereas T cell reactivity fluctuated randomly.

The antirheumatic drug disodium aurothiomalate inhibits CD4+ T cell recognition of peptides containing two or more cysteine residues.

The mechanism of action of antirheumatic gold drugs, such as disodium aurothiomalate (Au(I)TM), has not been clearly identified. Gold drugs inhibit T cell activation induced by mitogen and anti-CD3 mAb in vitro at relatively high concentrations. However, since gold drugs fail to induce immunosuppression in vivo, the pharmacologic relevance of this finding is doubtful.

Role of three quantitatively dominant endogenous peptides from HLA-DRB1*0401 molecules in class II specific alloreactivity.

Alloreactivity remains an important barrier to organ transplantation and is caused by T cell recognition of foreign histocompatibility antigens (HAg) in two ways: (1) indirect recognition, in which processed HAg peptides are presented by self MHC like any other foreign antigen, and (2) direct recognition, where the foreign MHC itself is recognized in contravention of the T cell recognition rule of self restriction. Whereas the role of endogenous peptides in direct MHC class I specific recognition is now established, their role in class II specific direct alloreactivity remains controversial, since no defined endogenous peptide has been shown to be required for alloreactivity. That mutations resulting in defective antigen processing impair class II specific allostimulation, however, suggests that the endogenous pathway is important for class II as well as class I alloreactivity.

Requirements for stimulation or anergy induction in alloreactive human T cell clones.

The "two signal" concept for T cell activation is widely accepted. Signal 1 is commonly delivered via the antigen receptor, and signal 2 via accessory interactions. Delivery of both signals results in activation, signal 1 alone in induction of hyporesponsiveness.

A 16mer peptide of the human autoantigen calreticulin is a most prominent HLA-DR4Dw4-associated self-peptide.

The human Ca(2+)-binding (storage) protein calreticulin, located in the lumen of the endoplasmic reticulum, is proposed to play a role as autoantigen: anticalreticulin autoantibodies occur in the sera of patients with SLE and patients with onchocerciasis (calreticulin shows a high sequence homology to the Onchocerca volvulus antigen RAL-1). Here we present sequencing data of a HLA-DR4Dw4-associated calreticulin peptide fragment, Cal(295-310), purified from a DR4Dw4 self-peptide pool. Cal(295-310) proved to be one of three commonest self-peptides associated with DR4Dw4 molecules that were isolated from the EBV-transformed B-cell line BSM (DR4Dw4, DRw53).

Ligand motifs of HLA-DRB5*0101 and DRB1*1501 molecules delineated from self-peptides.

Antigenic peptides are presented to CD4+ T cells by MHC class II molecules via a highly polymorphic peptide-binding groove. The two HLA-DR alleles isotypically expressed on HLA-DR15Dw2-positive cells, DRB1*1501 (DR2b) and DRB5*0101 (DR2a) molecules, show a number of differences in polymorphic residues of the beta-chain, including the Gly-Val-dimorphism at position beta 86. Therefore, different requirements for interaction of peptides with these alleles must be expected.

Self-peptides from four HLA-DR alleles share hydrophobic anchor residues near the NH2-terminal including proline as a stop signal for trimming.

Naturally processed MHC class II-associated peptides proved to be heterogeneous in size, varying from 13 to 25 amino acids. Truncation variants suggested sequence motifs that afford the amino termini to be shifted for obtaining an alignment: a 9- to 11-residue core region that is bordered by primary anchor residues is surrounded by extra sequences of variable lengths and hitherto unknown functions. Herein we present bulk sequencing analyses of self-peptides from four HLA-DR alleles and HLA-DQw7 clearly showing that the length of most of the NH2-terminal preanchor sequence is limited to 1 to 3 residues.

Characterization of peptides bound to extracellular and intracellular HLA-DR1 molecules.

Exogenous antigens are internalized by antigen-processing cells and processed within vesicular compartments to produce antigenic peptides that bind to newly synthesized MHC II molecules. These MHC class II peptide complexes are displayed at the plasma membrane and stimulate specific CD4+ T cells. In the present study, we established a method to isolate intracellular MHC molecules in a preparative scale (2-3 mg HLA-DR1) from endosomal compartments by Percoll density-gradient centrifugation.

Modulation of p145c-kit function in cells of patients with acute myeloblastic leukemia.

The function of the steel factor receptor, p145c-kit, in patient-derived acute myeloblastic leukemia (AML) cells was investigated. Steel factor stimulation of AML cells coexpressing p145c-kit and the progenitor cell antigen CD34 resulted in complete receptor down-regulation, a marked decrease of CD34 antigen expression, and the induction of the granulocyte lineage antigen CD15. These changes in surface marker expression paralleled morphological differentiation to granulated blasts and promyelocytes.

Evidence for cobinding of self- and allopeptides to human class II major histocompatibility antigen DR1 by energy transfer.

Purified human class II major histocompatibility antigen HLA-DR1 was subjected to high-performance gel filtration with fluorescence detection to investigate simultaneous binding of two classes of peptides: the N-terminally fluoresceinated allopeptides fluorescein isothiocyanate (FITC)-conjugated DR1 beta-(66-78) and FITC-conjugated DR3 beta-(66-78), derived from the third hypervariable region of the beta chain of DR1 and DR3, respectively, and the DR1-associated self-peptide SP3, carrying the fluorophor 7-amino-4-methyl-coumarin-3-acetic acid (AMCA) at the N terminus. By analyzing the dimer-associated fluorescence signals, we measured an interpeptide energy transfer AMCA-->FITC that proved to be peptide-specific: it did not occur after replacement of the allopeptide by the DR1-restricted peptide IM-(18-29) from influenza matrix protein, whereas it was restored by SP3, due to the high homology of SP3 and allopeptide. Transfer analyses with truncated AMCA-SP3 and AMCA-IM-(18-29) are consistent with Leu-3 being a common anchor residue of both peptides that allows an interaction with the hydrophobic specifity pocket around Ala-37 of the alpha 1 domain.

The T-cell repertoire in myasthenia gravis involves multiple cholinergic receptor epitopes.

Antibodies against the alpha-subunit of the acetylcholine receptor (AChR) are found in most patients with myasthenia gravis and are considered to contribute to the receptor damage which leads to the characteristic signs and symptoms of the disease. This B-cell response is T-cell driven. Elevated T-cell reactivities to AChR and its alpha-subunit have been described in myasthenia gravis, and AChR alpha-subunit peptide reactive T-cell lines and clones preferentially recognizing certain defined sequence segments have been reported, thereby disclosing the possibility of specific immunotherapy.

A continuous sequence of more than 70 amino acids is essential for antibody binding to the dominant antigenic site of glycoprotein gp58 of human cytomegalovirus.

Antigenic domain 1 (AD-1) on glycoprotein gp58 of human cytomegalovirus was characterized in detail, using mouse and human monoclonal antibodies as well as human convalescent sera. Series of procaryotically expressed fusion proteins and synthetic peptides of various lengths were used as sources of antigen. Binding of antibodies was found to depend on a continuous sequence of more than 70 amino acids between residues 552 and 635 of gp58.

Self-peptide released from class II HLA-DR1 exhibits a hydrophobic two-residue contact motif.

Peptide fragments of foreign and self-proteins are of great immunologic importance as their binding to major histocompatibility complex (MHC) class I or II molecules makes an interaction with a corresponding T cell receptor possible. Recently, allele-specific peptide sequence motifs proved to be responsible for MHC binding, no matter whether self- or non-self-antigens were involved. Up to now, all investigated human class II-associated peptides were derived from foreign antigenic proteins.

In vitro processing of insulin for recognition by murine T cells results in the generation of A chains with free CysSH.

Studies on the processing of insulin as an Ag for the presentation to MHC class II-restricted T cells revealed that the amino acid residues 1-14 of the insulin A chain are recognized by insulin-specific T cells. An A1-14 peptide containing three cys-residues that were protected by S-sulfonate groups still needed processing by APC for efficient presentation similar to native insulin. We suspected that reductive deblocking or opening of disulfide bonds that generates CysSH-residues may be an essential processing step for these Ag.

Tumor-specific antigens revisited: presentation to the immune system of fusion peptides resulting solely from tumor-specific chromosomal translocations.

Adaptive immune responses depend upon recognition by lymphocytes-T of short polypeptide sequences bound to major histocompatibility complex (MHC) molecules. Since endogenous intracellular proteins can be presented to the immune system in this way, any tumor-specific structure may function as a potentially tumor-specific antigen. Fusion proteins arising as a result of chromosomal translocations provide good candidates for novel tumor-specific antigens recognizable by the host immune system.

Self and foreign peptides interact with intact and disassembled MHC class II antigen HLA-DR via tryptophan pockets.

The acid release of endogenous peptides from immunoaffinity-pure human major histocompatibility complex (MHC) class II proteins HLA-DR1 is accompanied by an 18% decrease in intrinsic tryptophan fluorescence. The effect is totally reversible upon readdition of an autologous endogenous peptide fraction. High-performance size-exclusion chromatographic (HPSEC) binding and release studies with a nonfluorescent HLA-DR1-restricted influenza matrix peptide IM(18-29) prove the fact that Trp residues of the HLA protein change their fluorescence intensities.

Non-radioactive detection of MHC class II-peptide antigen complexes in the sub-picomole range by high-performance size-exclusion chromatography with fluorescence detection.

In order to avoid chemical or structural modification of T-cell epitopes by labelling, a high-performance size-exclusion chromatographic fluorescence binding assay was developed, based on the intrinsic Trp fluorescence of major histocompatibility complex (MHC) proteins. The increase in Trp fluorescence intensity of the isolated human MHC product HLA-DR 1 on complex formation with unlabelled influenza matrix peptide[18-29] (IM[18-29]) was examined. Binding of IM[18-29] to the heterodimeric form of HLA-DR 1 (Kd = 4.

Presentation of insulin and insulin A chain peptides to mouse T cells: involvement of cysteine residues.

The requirements for insulin presentation and recognition by A alpha b A beta b- and A alpha b A beta k-restricted mouse T cells were studied using a variety of derivatives of the insulin A chain. It was found that A chain peptides with irreversibly blocked Cys residues are non-stimulatory for the T cells. This suggests that at least one of the Cys residues is essential for recognition.

Solution conformation of thymosin beta 4: a nuclear magnetic resonance and simulated annealing study.

The conformation of the polypeptide thymosin beta 4 in solutions of 60% (v/v) trifluoroethanol-d3 and 50% (v/v) hexafluoroisopropyl-d2 alcohol in water is investigated by nuclear magnetic resonance (NMR) spectroscopy. Under these conditions thymosin beta 4 adopts an ordered structure. By use of a combination of two-dimensional NMR techniques, the 1H NMR spectrum of thymosin beta 4 is assigned.

Limit of T cell tolerance to self proteins by peptide presentation.

Cytotoxic T lymphocytes (CTLs) recognize foreign peptides bound to major histocompatibility complex (MHC) class I molecules. MHC molecules can also bind endogenous self peptides, to which T cells are tolerant. Normal mice contained CTLs specific for self peptides that were from proteins of ubiquitous or tissue-restricted expression.