PubMed Health⌕ Search

Biomedical subjects

K Falk

Publications and source records attributed to K Falk.

At least 73 records · Page 4Linked to original sources
PubMed1993

A prominent natural H-2 Kd ligand is derived from protein tyrosine kinase JAK1.

The first natural MHC ligand to be sequenced directly was the nonapeptide SYFPEITHI eluted from H-2 Kd molecules of a mouse tumour line, P815 [1]. A GenBank search indicated high homology to a nonapeptide contained within the human tyrosine kinase JAK1: SFFPEITHI, residues 355-363 [2]. This high homology prompted us to look at whether the mouse JAK1 protein has a Tyr residue at position 356 instead of Phe as in the human sequence. Cloning and sequencing of the mouse homologue gene confirmed that this is indeed the case. Thus, the physiological MHC ligand SYFPEITHI is derived from the protein tyrosine kinase, JAK1. The mouse tumor line P815 expresses the 5.4-kb JAK1 mRNA, and the 130,000 kDa JAK1 protein can be readily detected.

3T3 Cells↗
PubMed1993

MHC molecules as peptide receptors.

The central unit for regulation of the specific immune system is a trimolecular complex made up of the T cell antigen receptor, the MHC molecule, and the MHC ligand. The third component is a peptide derived as a degradation product from a protein. During recent years there has been some progress in understanding the interaction between MHC molecules and their peptide ligands: MHC molecules are peptide receptors of peculiar specificity, being able to accommodate millions of different peptides provided they share some common features.

Alleles↗
PubMed1993

Natural peptide ligand motifs of two HLA molecules associated with myasthenia gravis.

The peptide motifs of two HLA molecules, B8 and DR3(17), which are associated with autoimmune diseases including myasthenia gravis, were determined from natural peptide pools using Edman degradation. The majority of HLA-B8 ligands are nonamers preferentially terminated by leucine. As a characteristic feature of the HLA-B8 motif, there is a high degree of conservation of positively charged amino acids at position 3 and 5, exclusively lysine at position 3, and lysine or arginine at position 5. Additional evidence for this allele-specific motif is the presence of these features in several viral peptides recognized by HLA-B8 restricted T cells. The DR3(17) motif is characterized by four conserved anchor-like positions ordered in an almost symmetrical arrangement, as has been found for DR1 and DR5 motifs. A first hydrophobic/aromatic anchor three to four residues apart from the N-terminus (at relative position 1) appears to be a common feature of DR ligands. The second anchor is an aspartate at relative position 4, which is likely to be the DR3(17)-specific contact site in the groove. Two additional conserved positions closer to the C-terminus are occupied by charged amino acids at relative position 6 and by hydrophobic/aromatic residues at positions 8, 9, or 10. Eight individual naturally processed DR17 ligands were sequenced and were found to be derived from exogenous proteins and cytoplasmic membrane receptors. These natural peptides conform well to the determined motif. A single exchange of the anchor-like positions in a model peptide abrogated binding to DR17+ cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Comparison of the H-2Kk- and H-2Kkm1-restricted peptide motifs.

Self-peptide pools eluted from purified H-2Kk or H-2Kkm1 molecules were sequenced. The majority of self-peptides associated with H-2Kk molecules were found to be octamers with two anchor positions. Position 2 is invariantly occupied with Glu, and the C-terminal residue at position 8 is almost always Ile. Comparison of this motif with synthetic peptides known to contain viral or parasite T-cell epitopes could be well aligned with this motif, except that the C-terminal Ile residue frequently appears to be at position 9 of the aligned sequences, instead of 8. Self-peptides eluted from mutant H-2Kkm1 molecules also appear to be mostly octamers with the same Ile residues at position 8 as with Kk. Position 2 is still dominantly occupied by Glu; in contrast to the Kk motif, however, Gln, Gly, and Pro are also allowed. Other differences between the two motifs indicate that a certain number of peptides presented by one of the molecules are not presented by the other.

Amino Acid Sequence↗
PubMed1993

Peptides naturally presented by MHC class I molecules.

MHC class I molecules are peptide receptors of stringent specificity which however still allow millions of different ligands. This is achieved by the following specificity characteristics summarized as allele specific peptide motifs: Peptides are of defined length, depending on the class I allele (either 8 or 9 residues; exceptions have been observed). Typically, 2 of the 8 or 9 positions are anchors that can only be occupied by a single amino acid residue, or by residues with closely related side chains. Location and characteristics of anchors vary with class I alleles. The C terminus of the peptide ligands is frequently an aliphatic or charged residue. Such allele-specific class I peptide ligand motifs, known so far for H-2Kd, Kb, Kk, Kkm1, Db, HLA-A*0201, A*0205, and B*2705, are useful to predict natural T cell epitopes. The latter can be determined by extraction from cells recognized by the T cell of interest. It is not known how the class I ligands are produced in the cell, although speculative models exist. The peptide specificity of class I molecules and experimental evidence indicate that T cells are tolerant to only a small fraction of the expressed genomic sequences and are not tolerant to the remainder. The function of class I molecules is to present a collection of self-peptide samples at the cell surface for surveillance by T cells.

Amino Acid Sequence↗
PubMed1992

Gene transfer experiments imply instructive role of major histocompatibility complex class I molecules in cellular peptide processing.

DBA/2-derived mouse tumor cells were transfected with the H-2 Kb gene. Naturally processed minor histocompatibility (H) peptides were extracted from both transfected and non-transfected cells by acid elution, and were separated by high-performance liquid chromatography. Kb-restricted minor H epitopes corresponding to H-4b and mapki, both encoded by non-major histocompatibility complex genes of DBA/2, were readily detected by the respective cytotoxic T lymphocyte in peptides extracted from Kb-transfected, but not from non-transfected or Db-transfected cells. Titration experiments indicated at least 3000-fold less copies of correctly processed Kb-restricted epitopes in cells without Kb as compared to cells with Kb. Since we estimate the copy number of Kb-restricted H-4b epitopes in Kb-expressing transfectants to be less than 1000 per cell, the pool size of H-4b epitopes correctly processed in the absence of Kb should be less than 1/3 copy per cell.

Animals↗
PubMed1992

Specificity of antigen processing for MHC class I restricted presentation is conserved between mouse and man.

Alloreactive mouse cytotoxic T lymphocytes (CTL) specific for particular peptides presented by H-2Kb molecules on mouse cells were found to recognize human cells transfected with Kb. The CTL-recognized peptides (probably derived from conserved proteins) were extracted from Kb-expressing human or mouse cells, respectively, and compared biochemically by high resolution high performance liquid chromatography. The results strongly suggest identity of peptides processed by cells from both species and thus indicate that the specificity of the processing machinery used in the major histocompatibility complex (MHC) class I-restricted pathway, probably including enzymes, transport mechanisms, and chaperons, is highly conserved across species. The results are consistent with the notion that MHC molecules themselves have an instructive role in processing.

Animals↗
PubMed1992

Peptide motifs of closely related HLA class I molecules encompass substantial differences.

The peptides presented by major histocompatibility complex class I molecules adhere to strict rules concerning peptide length and occupancy by certain amino acid residues at anchor positions. Peptides presented by HLA-A*0201 molecules, for example, are generally nonapeptides requiring Leu or Met at position 2 and an aliphatic residue, predominantly Val, at position 9. A closely related molecule, HLA-A*0205, differing from the former at four amino acid residues, has a related but substantially different peptide motif. A*0205-presented peptides are still nonapeptides, and position 9 is still aliphatic, although it is preferentially occupied by Leu instead of Val. Position 2 not only allows aliphatic residues but also polar ones. Occupancy at position 6, considered as an auxiliary anchor in A*0201, as well as non-anchor residues at positions 3, 4, and 8 are relatively well conserved between the two peptide motifs. Thus, although a number of the T cell epitopes presented by the two HLA-A2 forms is expected to be identical, a considerable number of epitopes should be different.

Amino Acid Sequence↗
PubMed1992

A self peptide naturally presented by both H-2Kb and H-2Kbm1 molecules demonstrates MHC restriction of self tolerance at the molecular level.

An alloreactive CTL clone, 27.B2, produced in the mouse strain combination B6.C-H-2bm1 (bm1) against C57BL/6 (B6) and nominally directed against the Kb molecule has been shown to be peptide dependent. The clone recognizes intact B6, but not intact bm1 or bm3 target cells. However, peptides recognized by 27.B2 CTL can be extracted from bm1 or B6 whole cell lysates as well as from purified Kbm1 or Kb molecules. The target peptides recognized by 27.B2 appear to be identical, whether isolated from Kbm1- or Kb-expressing cells, as shown by identical behavior upon high-resolution reversed-phase HPLC separation. Thus, the same peptide is presented by different MHC molecules including Kb and Kbm1, but is recognized by 27.B2 CTL only in the context of the foreign molecule, Kb, and not in the context of the self molecule, Kbm1.

Animals↗
PubMed1991

Fine specificity of cytotoxic T lymphocytes primed in vivo either with virus or synthetic lipopeptide vaccine or primed in vitro with peptide.

Standard synthetic peptide preparations contain numerous peptidic byproducts in small amounts, which may be efficiently recognized by cytotoxic T lymphocytes (CTL). Recognition patterns of such peptide mixtures by CTL may serve as a kind of fingerprint for CTL fine specificity. Three types of H-2Db-restricted CTL were compared in this way. CTL primed in vivo either with A/PR/8/34 influenza virus or with a synthetic lipopeptide vaccine prepared from influenza nucleoprotein (NP) peptide 365-380 showed identical fine specificity. Both recognize virus-infected cells. In contrast, CTL primed in vitro with NP 365-380 had a different fine specificity and they did not recognize virus-infected cells. Most significantly, the two in vivo primed CTL types efficiently recognized the natural viral nonapeptide NP 366-374 presented by virus-infected H-2b cells, whereas the in vitro primed CTL failed to do so.

Animals↗
PubMed1991

On the nature of peptides involved in T cell alloreactivity.

The strong reaction of T cells against foreign major histocompatibility complex (MHC) antigens, commonly termed "alloreactivity", is not only a nuisance for clinical organ transplantation; it also remains a puzzling question for immunologists. By making use of recent technical developments, alloreactive T cells nominally directed against a mutation in a single MHC class I molecule were found to fall into several major categories. One is recognizing peptides whose occurrence is dependent on one particular MHC allele, another is recognizing peptides supported by several MHC alleles, and a third is recognizing peptides occurring independently of MHC alleles. In a fourth category, the binding to MHC of any of a broad range of peptides appears sufficient. In addition, there are T cells for which no peptide involvement could be detected at all. Even within these categories, the heterogeneity of T cells is considerable: among 16 Kb-reactive T cells analyzed, 15 different modes of reactions were found.

Alleles↗
PubMed1991

Identification of naturally processed viral nonapeptides allows their quantification in infected cells and suggests an allele-specific T cell epitope forecast.

Virus-specific cytotoxic T lymphocytes (CTL) recognize virus-derived peptides presented by major histocompatibility complex (MHC) class I molecules on virus-infected cells. Such peptides have been isolated from infected cells and were compared to synthetic peptides. We found previously the Kd- or Db-restricted natural influenza nucleoprotein peptides to coelute on reversed phase high performance liquid chromatography columns with certain peptidic by-products present in synthetic peptide preparations. Here we show by extensive biochemical and immunological comparison that the natural peptides in all respects behave as the surmised synthetic nonapeptides, and thus, must be identical to them. The absolute amounts of these natural peptides contained in infected cells could be determined to be between 220 and 540 copies by comparing with defined amounts of pure synthetic nonapeptides. The comparison of the natural Kd-restricted peptide with published synthetic peptides known to contain other Kd-restricted CTL epitopes suggested a new MHC allele-specific T cell epitope forecast method, based on the defined length of nine amino acid residues and on critical amino acid residues at the second and the last position.

Alleles↗
PubMed1991

Allele-specific motifs revealed by sequencing of self-peptides eluted from MHC molecules.

The crystal structures of major histocompatibility complex (MHC) molecules contain a groove occupied by heterogeneous material thought to represent peptides central to immune recognition, although until now relatively little characterization of the peptides has been possible. Exact information about the contents of MHC grooves is now provided. Moreover, each MHC class I allele has its individual rules to which peptides presented in the groove adhere.

Alleles↗
PubMed1991

Uneven tissue distribution of minor histocompatibility proteins versus peptides is caused by MHC expression.

Naturally processed minor histocompatibility (H) peptides corresponding to H-4b, H-Y, and an unmapped BALB.B minor H gene were quantified in a relative way in 15 different tissues of male BALB.B mice. For one of these minor H antigens, we could also determine the relative content of the respective protein. For each minor H peptide, an individual tissue distribution was found. Tissues expressing little or no MHC (major histocompatibility complex), like brain, contained only small amounts of minor H peptides or none at all, although the same tissues contained minor H protein in substantial quantities. By contrast, Kb-expressing brains from mice transgenic for Kb under control of the glial acidic protein promoter contained both minor H peptide and protein in high amounts. Thus, the expression of minor H peptides in a given tissue is dependent on coexpression of the restricting MHC class I molecules.

Animals↗
PubMed1991

SCID mouse model of Epstein-Barr virus-induced lymphomagenesis of immunodeficient humans.

Immunodeficient humans are at very high risk of developing Epstein-Barr virus (EBV)-induced lymphomagenesis. Severe combined immunodeficient mice (SCID) have been shown to develop lymphoproliferative disease (LPD) following transfer of peripheral blood leukocytes (PBL) with latent EBV. To study mechanisms of lymphomagenesis, we compared results of engraftment of PBL from normal donors and immunodeficient donors with X-linked lymphoproliferative disease (XLP). Graft-versus-host disease (GVHD) developed in 6 of 10 SCID mice 4 to 8 weeks following transfer of PBL from normal donors. In contrast, none of 9 mice engrafted with PBL from XLP patients with T-cell defects showed GVHD. LPD developed in mice regardless of the immune competence of the donors. The expression of EBV-encoded proteins, results of immunophenotyping, and karyotyping of the LPD lesions revealed lethal oligoclonal LPD owing to transfer of latent EBV in B cells in mice engrafted with PBL from seropositive donors. Polyclonal LDP developed in mice engrafted with PBL from seronegative patients which were infected with B95-8 virus 6 weeks after transfer of the cells. This model is useful for investigating mechanisms of EBV-induced LDP in immunodeficient patients.

Animals↗
PubMed1991

Exact prediction of a natural T cell epitope.

T lymphocytes recognize their antigen as peptides associated with major histocompatibility complex (MHC) molecules. Peptides naturally presented by MHC class I molecules are uniform in length and have a specific motif, both defined by the respective MHC allele (Falk, K. et al. Nature 1991. 351:290). These allele-specific motifs should allow exact prediction of natural T cell epitopes. H-2Kb-restricted epitopes, for example, have a length of eight amino acid residues and conserved anchor residues at positions 5 and 8. According to this information, we predicted the natural Kb-restricted epitope of ovalbumin, thought to be contained in the 19-mer IINFEKLTEWTSSNVMEER, to be SIINFEKL. Here we show that this prediction is correct. Thus, exact prediction of natural T cell epitopes is possible.

Amino Acid Sequence↗