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H Kalbacher

Publications and source records attributed to H Kalbacher.

At least 55 records · Page 3Linked to original sources
PubMed1997

T cell response to myelin basic protein in the context of the multiple sclerosis-associated HLA-DR15 haplotype: peptide binding, immunodominance and effector functions of T cells.

In this study, we evaluated the role of the two functional HLA-DR heterodimers, DR2a (DR alpha paired with the beta chain encoded by DRB5*0101) and DR2b (DR alpha paired with the beta chain encoded by DRB1*1501), that are coexpressed in the multiple sclerosis (MS)-associated haplotype HLA-DR15 Dw2, in presenting myelin basic protein (MBP) peptides to MBP-specific T cell lines (TCL). Our results show that both HLA-DR molecules serve as restriction elements for HLA-DR15-restricted TCL. Slightly higher numbers of TCL use DR2a as restriction element, and the epitopes contained in the immunodominant C-terminal region (131-159) are uniquely restricted by DR2a. The immunodominant middle epitope (81-99) is recognized in the context of both DR2a and DR2b, but this specificity strongly dominates the DR2b-restricted T cell response. Overall, immunodominance in the MBP-specific T cell response correlated well with peptide binding to DR2a or DR2b, demonstrating that the affinity of MHC-peptide interactions is important for shaping the T cell response to this autoantigen. Furthermore, we show that binding of the middle MBP peptide to HLA-DR15 molecules prevents cleavage by cathepsin D, a protease abundantly found in endosomal processing compartments, and thus contributes to its immunodominance. Surprisingly, the restriction element employed by MBP-specific T cell clones influenced the effector function (i.e., cytotoxic activity) of T cells irrespective of their peptide fine specificity.

Alleles↗
PubMed1997

Presence of argininosuccinate synthetase in glial cells as revealed by peptide-specific antisera.

The presence and the possibility of induction of argininosuccinate synthetase in a glial cell line were investigated. For this purpose, antisera were produced against peptides representing partial sequences 196-222 and 337-349, respectively, of the mouse liver enzyme. Both antisera were shown to be monospecific for argininosuccinate synthetase. In Western blot experiments, immunoreactivity was found in mouse liver and brain homogenates. Only weak immunoreactivity was detectable in homogenates of cultured glioma cells, C6-BU-1. However, when the glioma cells were treated with either bacterial lipopolysaccharide, interferon-gamma, or a combination of both, argininosuccinate synthetase immunoreactivity was increased. The findings demonstrate that this enzyme is present in glial cells and is induced under conditions which stimulate persistent production of nitric oxide. The antisera will be a valuable tool for further investigations on arginine synthesis in brain as well as peripheral cells.

Animals↗
PubMed1996

BCR/ABL leukemia oncogene fusion peptides selectively bind to certain HLA-DR alleles and can be recognized by T cells found at low frequency in the repertoire of normal donors.

Chronic myelogenous leukemia (CML) is characterized by the t(9;22) translocation that results in chimeric genes encoding bcr/abl fusion proteins. Junction-spanning sequences represent unique tumor-specific moieties that might be exploited therapeutically. We investigate here the binding of synthetic bcr/abl peptides to various HLA-DR alleles and their recognition by T cells from normal donors and CML patients. A 23-mer b3/a2 peptide bound very strongly to isolated HLA-DRB1*1101 (Dw5) and relatively strongly to DRB1*0301 (Dw3) and DRB1*0402 (Dw10) molecules, as estimated using a competition assay. It failed to bind to several other DR alleles, including three different DR4 alleles. In contrast, a 23-mer b2/a2 peptide bound only to the DRB1*0301 (Dw3) allele. Peripheral blood mononuclear cells from normal donors were sensitized in vitro against the b3/a2 peptide. After four repetitive stimulations, T cells responding to the peptide were found at low frequency in 5 of the 11 donors tested. Three of the five were HLA-DR11+, and all three of the DR11+ donors tested were found to respond. T cells recognizing bcr/abl peptides were not identified in any of the CML patients studied, regardless of HLA type. Finally, even peptide-reactive T-cell lines from normal donors were not stimulated by native CML cells in the absence of exogenous peptide. These results show the presence of low-frequency major histocompatability complex class II-restricted bcr/abl-responses in the normal T-cell repertoire of donors with certain HLA types, but suggest that unmodified tumor cells cannot be recognized by such peptide-sensitized T cells.

Amino Acid Sequence↗
PubMed1996

New ligands binding to the human leukocyte antigen class II molecule DRB1*0101 based on the activity pattern of an undecapeptide library.

Major histocompatibility complex (MHC) class II molecules present peptide antigens to CD(4+)-T cells. These heterogeneous peptides are derived from internalized exogenous proteins or from endogenous membrane proteins that are processed by the antigen-presenting cell. Peptides are bound to the MHC class II molecules in an extended conformation and extend out of the binding groove. The aim of this study was to estimate the influence of every amino acid in all the possible undecapeptide amides (2.048 x 10(14) individuals) on the binding to human MHC-DRB1*0101 molecules (HLA-DR1) and to identify new peptide ligands. 220 undecapeptide sublibraries, O/X10, each composed of ten degenerate positions and one defined position, were screened for binding to isolated HLA-DR1. Competition of the sublibraries with a fluorescence-labeled peptide ligand allowed definition of the amino acids favourable or unfavourable for DR1-binding at every sequence position. From the activity pattern of the undecapeptide library, 54 individual peptides were deduced (27 potential hits and 27 potential falls) and prepared by chemical synthesis. As anticipated, 27 positive and 27 negative results were obtained from the competition experiments. The 27 peptides that bind obey the rules for the HLA-DR1-binding motif. The synthetic peptide library approach proved to be valuable for the design of synthetic MHC class II ligands and thus can be considered as a basis for drug design in immunotherapy.

Amides↗
PubMed1996

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). Here we show that alteration by Au(III) of a model antigen, bovine ribonuclease (RNase)A, results in T cell sensitization to cryptic peptides of this protein. Upon immunization of mice with Au(III)-pretreated RNase [RNase/Au(III)], CD4+ T cell hybridomas specific for RNase/Au(III) were obtained in addition to those recognizing the immunodominant peptide RNase 74-88; the latter also were obtained after immunization with native RNase. RNase/Au(III)-specific T cell hybridomas reacted against RNase/Au(III) and RNase denatured by S-sulfonation of cysteine residues, but not against native RNase, or RNase pretreated with Au(I), A1(III), Cu(II), Fe(II), Fe(III), Ni(II), Mn(II), or Zn(II). Using a panel of overlapping, synthetic RNase peptides which were devoid of gold or gold-induced modifications, epitope mapping revealed that RNase/Au(III)-specific T cell hybridomas recognized the cryptic peptides 7-21 and 94-108, respectively. Comparison of the proliferative response of bulk CD4+ T cells, prepared from splenocytes after immunization with either RNase/Au(III) or native RNase, revealed that Au(III) pretreatment of RNase led to a markedly enhanced response to the two cryptic peptides while it did not influence the response to the immunodominant peptide. The cryptic peptides were also presented after preincubation of bone marrow-derived macrophages with RNase and Au(I), but not with RNase alone, suggesting that oxidation of Au(I) to Au(III) and subsequent protein alteration by Au(III) can happen in mononuclear phagocytes. We conclude that Au(III) alteration of proteins alters antigen processing and, thus leads to presentation of cryptic peptides. This mechanism may shed light on the development of allergic and autoimmune side effects of Au(I) anti-rheumatic drugs. In addition, it might provide a general mechanism of how metal ions act as T cell sensitizers.

Amino Acid Sequence↗
PubMed1996

Analysis of T helper cell response to glycoprotein H (gpUL75) of human cytomegalovirus: evidence for strain-specific T cell determinants.

The proliferative response of helper T cells against glycoprotein H (gH; gpUL75) of human cytomegalovirus (HCMV) was determined in T cell lines from 5 healthy HCMV-seropositive donors. A differential response in two lines was noted when gH from strain AD169 or Towne was used as antigen. T cell-reactive domains between aa 15 and 510 were identified using beta-galactosidase fusion proteins containing overlapping fragments of gH, and they were confirmed with synthetic peptides as stimulating antigen. T cell proliferation was observed with antigens containing aa 34-51, 111-142, 284-302, 324-342, and 454-510 of gH. None of the determinants stimulated all donors. The T cell epitope defined by aa 34-51 is located in close proximity to a strain-specific dominant B cell epitope; however, no strain dependence for this T cell determinant was observed. In contrast, the dominant T cell response against aa 284-302, which was observed in three T cell lines, was strain specific.

Amino Acid Sequence↗
PubMed1996

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. Potential DR1-restricted epitopes were mapped using an MHC competition binding assay. Both the proliferation and the binding data identified a DR1-restricted T cell epitope (F51-65). Contact sites of the peptide HQSLVIKLMPNITLL with MHC were characterized using substitution analogs. Alanine substitutions at most positions did not interfere with F51-65 binding. These analogs were therefore useful for studying the residues which were recognized by the TCR of MV- and F51-induced T cells lines. In addition to amino acid residues of the core of peptide F51-65 both the C-terminal and the N-terminal amino acids were essential for T cell interaction. Since peptides presented by class II molecules vary in length, these findings suggest that residues of the ragged tail are important for T cell activation. It is speculated that in late convalescent donors the length of the flanking sequence of MHC II-restricted peptides may play a role in controlling the heterogeneity of MV-specific T cell clones recruited as T helper/memory cells.

Adult↗
PubMed1995

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. J. 1991, 280, 533). CNBr cleavage of the pig receptor protein for peptide sequencing revealed peptide sequences which demonstrate that the 42 kDa InsP4 receptor is a novel protein. Two synthetic peptides derived from the pig receptor were used to generate peptide-specific antisera which recognized also the intact receptor protein from pig. The two antisera showed different reactivity with the InsP4 receptor purified from pig and human compared to sheep, beef, and rat. This indicates a species heterogeneity of this protein.

Amino Acid Sequence↗
PubMed1995

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. In cerebellar membranes, the antibodies clearly recognized the 42 kDa Ins-P4 receptor protein and two additional proteins (25 kDa, 37 kDa) which still have to be identified. The anti-peptide antibodies could selectively immunoprecipitate the Ins-P4 receptor protein. The antiserum was used (i) to demonstrate that in brain from different species (human, pig, beef, rat, mouse and sheep) a similar 42 kDa Ins-P4 receptor protein is contained, and (ii) to obtain indications for the existence of a related soluble form of the 42 kDa Ins-P4 receptor besides the membrane-associated receptor.

Amino Acid Sequence↗
PubMed1995

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. In this study, we asked whether Au(I)TM interferes with processing and presentation of defined Ags to T cells. Using a panel of murine CD4+ T cell hybridomas, we found that low concentrations of Au(I)TM (< or = 10 microM) led to a markedly reduced IL-2 release of T cell hybridoma clones that recognized peptides containing two or more cysteine (Cys) residues, such as bovine insulin A1-14. Since disodium thiomalate alone had no effect, the inhibition was due to Au(I). IL-2 production induced by anti-CD3 mAb stimulation was not affected by the low concentration of Au(I)TM used. Au(I)TM had no effect on the presentation of peptides containing no or only one Cys residue(s). In contrast to the unmodified insulin peptide A1-14, Au(I) could not inhibit recognition of an insulin peptide in which Cys residues in positions 6 and 11 were replaced by serine. Most likely, the observed inhibition is mediated by formation of chelate complexes between Au(I) and two Cys thiol groups of the affected antigenic peptides. The peptide-specific inhibitory effect of Au(I) on Ag presentation described here might contribute to the therapeutic effect of Au(I) compounds in rheumatoid arthritis.

Amino Acid Sequence↗
PubMed1995

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. Despite the high level of T cell reactivity to autologous tumor cells in short-term (6 days) culture, 1) they failed to respond to synthetic peptides corresponding to the bcr/abl fusion sequence of the patient, and 2) only one proliferative T cell clone (TCC) was isolated which specifically recognized HLA-DR-matched CML cells. This TCC appeared not to recognize synthetic peptides corresponding to the bcr/abl fusion sequence of the patient; the antigen to which it responds remains unknown. To assess potential immunogenicity of bcr/abl peptides, it was attempted to sensitize T cells from normal donors in vitro. Of 109 cell lines obtained from seven different donors, eleven showed peptide-dependent proliferation. Therefore, although these results show that it is possible to isolate apparently CML-specific T cells from patients, as well as to prime T cells against tumor-specific peptide in vitro, the frequency of such T cell-mediated reactivity appears low and its relevance to anti-leukemic effects questionable. On the other hand, the strong time-dependent enhancement of natural killing of autologous CML blasts during IFN-alpha treatment, a phenomenon not observed for T cell reactivity, suggests that natural immunity may be more important in controlling disease.

Amino Acid Sequence↗
PubMed1994

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. The nature of signal 1 in alloreactivity is not completely clear; most evidence suggests that a complex of foreign major histocompatibility complex molecules and their bound peptides is recognized. Interactions between B7 (CD80) ligand and CD28/CTLA-4 receptors are currently considered the most important sources of signal 2. Xenogeneic cells transfected with human genes provide useful stimulators for dissecting signals 1 and 2 in alloreactivity. We show here that the majority of DR-specific alloreactive T cell clones (TCC) fails to recognize Chinese hamster ovary (CHO) cells transfected with human DR, whether or not these are cotransfected with genes for CD80 or LFA-3. Stimulation was not observed even in the presence of a pool of peptides isolated by low pH release from B cell line (BCL)-derived DR molecules, or in the presence of synthetic peptides corresponding to the sequences of the three most commonly identified endogenous peptides. Lack of recognition was observed both in failure to stimulate proliferation and in failure to induce anergy. However, one TCC was identified which responded weakly to DR+ CHO cells, and for this clone, the presence of either CD80 or LFA-3 strongly enhanced proliferative responses. Anergy was not induced, even in the absence of CD80. Immobilized HLA-DR molecules purified from a BCL also failed to stimulate proliferation, but unlike the CHO transfectants, they did induce anergy. Stimulation with BCL also induced anergy if CD80-dependent interactions were blocked with soluble CTLA-4-Ig receptor. These results are consistent with the model that DR molecules expressed in the absence of appropriate peptide are simply not recognized by most alloreactive T cells, whereas DR molecules containing appropriate bound peptide are recognized as signal 1 and induce anergy. CTLA-4-Ig blocking confirms that CD80-dependent interactions can be important in preventing anergy induction, but that they are not always necessary is illustrated by the existence of a single clone which recognized DR molecules on CHO transfectants, giving very weak proliferation without CD80, and nonetheless no anergy induction.

Amino Acid Sequence↗
PubMed1994

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. In this study, naturally processed self-peptides were eluted from purified HLA-DR15Dw2 molecules and related to DRB1*1501 or DRB5*0101 molecules by binding assays. An alignment of self-peptides and foreign peptides allowed the delineation of putative anchor motifs. N- and C-terminally truncated and alanine-substituted derivatives of the DR15Dw2 restricted myelin basic protein epitope MBP(85-105) confirmed their validity. Thus, DRB5*0101 requires a bulky hydrophobic residue (F or Y) at position i as a primary anchor, and Q or an aliphatic residue, such as V, I, or M, at position i + 3; positively charged residues at positions i + 7 and i + 8 are secondary anchors. For DRB1*1501, a nonaromatic, hydrophobic anchor (L, V, or I) at position i is supplemented by a bulky hydrophobic residue (F or Y) at position i + 3 as primary anchor; an additional hydrophobic side chain represented by M, I, V, or F occurs at position i + 6. Therefore, MBP(85-105) seems to contain two MHC interaction sites for DRB1*1501 and DRB5*0101, respectively, that may contribute to its immunodominance. Because HLA-DR15 Dw2 is associated with susceptibility to develop multiple sclerosis, the delineation of ligand motifs of the two DR2 alleles may help to study the interaction between potential autoantigenic peptides and these molecules in the future.

Alleles↗
PubMed1994

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). We tested the binding of Cal(295-309) and the analogous RAL-1 peptide to HLA-DR molecules: Cal(295-309) exhibited specific binding characteristics for DR4Dw4. Binding assays using self-peptide analogues with replaced amino acids led us to a DR4Dw4-binding motif with anchor residues at relative positions 1 and 6. The sequencing data suggest that calreticulin is a frequently processed intracellular protein. The abundance of calreticulin makes the presentation of different calreticulin peptides associated with HLA-D molecules likely to occur, supporting the immunologic relevance of this molecule.

Amino Acid Sequence↗
PubMed1994

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. We attempted to establish the importance of endogenous peptides for alloreactivity by identifying common sequences of peptides bound by DR molecules of an HLA-DRB1*0401 homozygous B cell line. Peptides corresponding to three of these (calreticulin, HLA class I and an unidentified molecule) were used to restimulate established allospecific HLA-Dw4 reactive T cell clones, as well as to sensitize allogeneic T cells de novo in vitro. Xenogeneic chinese hamster ovary (CHO) cells coexpressing the relevant DR allele together with CD80 were used as antigen presenting cells. The role of CD80 could be determined on these cells because (1) they are xenogeneic and (2) they do not express B7 family members bound by CTLA-4Ig.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

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. Most strikingly, proline is the dominant residue reappearing at positions 2 and 3 in any allele. Proline revealed to function as a stop signal for NH2-terminal trimming as well as a secondary anchor: crude cytosolic and endosomal peptide fractions could be processed by aminopeptidases in vitro, whereupon DR1 binding peptides with increased affinity were generated. In addition, aminopeptidase treatment of DR1: self-peptide complexes implied that proline together with sterical constraints of the MHC molecule do protect the peptides' NH2-termini from further processing, whereas their COOH-termini were accessible to cathepsin B processing. Finally, bulk sequencing profiles contained signals from further putative anchor residues clustering in the NH2-terminal region:tyrosine, phenylalanine, leucine, isoleucine, and valine are enriched at positions 2 to 4 in DR1, DR5, and DR6, however, at positions 4 to 6 in DR3. Isotype-specificity is demonstrated by DQw7 displaying glutamine and asparagine at position 2. Obviously, the degenerate occurrence of aromatic or aliphatic side chains close to the NH2-terminal guarantees for essential interactions with a hydrophobic pocket of the investigated DR molecules. Most probably, this pocket is located in the nonpolymorphic DR alpha-chain rationalizing previous findings of promiscuous peptide binding to different DR alleles.

Alleles↗
PubMed1993

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. Interestingly, the same phenotype was achieved by IL-3 stimulation of AML cells. p145c-kit extracellular domain-specific antibodies had either blocking or enhancing effects on ligand binding, receptor phosphorylation and down-regulation, and induction of cell proliferation. Correlations of these phenomena with distinct effects of antibody stimulation on cell substrate phosphorylation provide clues for the dissection of the p145c-kit signal and the analysis of its relevance for AML.

Animals↗