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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Interphotoreceptor retinoid-binding protein (IRBP), a retinal-specific Ag, induces experimental autoimmune uveitis in a variety of animals. We have previously shown that sequence 1169-1191 of bovine IRBP is the immunodominant epitope of this protein in Lewis rats and is highly immunogenic and uveitogenic in these rats. The active site of peptide 1169-1191 was determined by testing its truncated forms. The shortest peptide to be immunologically active was found to be 1182-1190 (WEGVGVVPD). To determine the role of individual residues of this sequence, we have tested the immunologic activities of nine analogs of peptide 1181-1191, in which each of residues 1182-1190 was substituted with alanine (A). The tested activities included the capacity to induce experimental autoimmune uveitis and cellular responses in immunized rats, as well as the capability to stimulate lymphocytes sensitized against IRBP or the parent peptide 1181-1191. Analogs that did not stimulate these lymphocytes were also tested for their capacity to competitively inhibit the proliferative response to 1181-1191. Analogs A(1184), A(1186), and A(1187) resembled 1181-1191 in their activities, whereas the other analogs exhibited remarkably reduced activities, with several patterns being noticed. Analog A(1182) was inactive in all tests. Analog A(1190) was very weakly uveitogenic and non-immunogenic, but it stimulated lymphocytes sensitized against IRBP or 1181-1191 when added at exceedingly high concentrations. Analogs A(1183) and A(1185) resembled A(1190) in being weakly uveitogenic and A(1185) was also found to be poorly immunogenic. In addition, relatively high concentrations of A(1183) and A(1185) were needed to stimulate lymphocytes sensitized against IRBP or 1181-1191. However, a different pattern of activities was exhibited by analogs A(1188) and A(1189). These peptides were uveitogenic and immunogenic, but failed to stimulate lymphocytes sensitized to IRBP or 1181-1191. Furthermore, A(1188) and A(1189), but not A(1182), also inhibited the response to 1181-1191 of a cell line specific toward this parent peptide. The data are interpreted to show that residues 1188 and 1189 are involved in the interaction of the peptide with the TCR, whereas residues 1182 and 1190 and, perhaps, 1183 and 1185, are pivotal for the binding of peptide 1181-1190 to the MHC molecules on APC.
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PMID:Analysis of the pivotal residues of the immunodominant and highly uveitogenic determinant of interphotoreceptor retinoid-binding protein. 170 28

We report on a computer algorithm capable of predicting the location of T-helper-cell epitopes in protein antigen (Ag) by analysing the Ag amino acid sequence. The algorithm was constructed with the aim of identifying segments in Ag which are resistant to proteolytic degradation by the enzymes cathepsin B, L, and D. These are prominent enzymes in the endocytic pathway through which soluble protein Ag enter APC, and resistant segments in Ag may, therefore, be expected to contain more T-cell determinants than susceptible segments. From information available in the literature on the substrate specificity of the three enzymes, it is clear that a cysteine is not accepted in any of the S2, S1, S1', and S2' subsites of cathepsin B and L, and not in the S1 and S1' subsites of cathepsin D. Moreover, we have noticed that cysteine-containing T-cell determinants in a number of protein Ag are particularly rich in the amino acids alanine, glycine, lysine, leucine, serine, threonine, and valine. By searching protein Ag for clusters of amino acids containing cysteine and two of the other amino acids we were able to predict 17 out of 23 empirically known T-cell determinants in the Ag with a relatively low number of false (positive) predictions. Furthermore, we present a new principle for searching Ag for potential amphipatic alpha-helical protein segments. Such segments accord well with empirically known T-cell determinants and our algorithm produces a lower number of false positive predictions than the principle based on discrete Fourier transformations previously described.
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PMID:T-helper-cell determinants in protein antigens are preferentially located in cysteine-rich antigen segments resistant to proteolytic cleavage by cathepsin B, L, and D. 171 25

NMR spectroscopy has been used to characterize a new renal cell line, TALH-SVE.1, which is derived from the medullary thick ascending limb of Henle's loop. From the 31P-NMR spectrum of a suspension of TALH-SVE cells using the chemical shift of the intracellular inorganic phosphate a value of 7.24 +/- 0.04 for the steady-state intracellular pH (pHi) was determined at pHo = 7.40. In addition, the 31P-NMR spectrum indicated rather high levels of UDPG, a finding confirmed by 1H-NMR spectra of perchloric acid extracts. The 1H-NMR data also demonstrate the presence of 'organic osmolytes' such as inositol, sorbitol, choline and glycerophosphoryl choline (GPC). 13C-NMR spectra of perchloric acid extracts of TALH-SVE cells incubated with [2-13C]- and [3-13 C]alanine were used to determine the relative influx in the Krebs cycle via pyruvate carboxylase (PCB) versus the influx via pyruvate dehydrogenase (PDH). The ratio was 0.41, while about 52% of all acetyl-CoA entering the Krebs cycle was unlabeled. 13C-NMR experiments also indicated that TALH-SVE cells lack gluconeogenic activity. The NMR study presented indicates that TALH-SVE cells possess metabolic pathways similar to those of the parental cells.
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PMID:An NMR spectroscopic characterization of a new epithelial cell line, TALH-SVE, with properties of the renal medullary thick ascending limb of Henle's loop. 184 3

Apamin is a single-chain, disulfide-bonded, 18-amino acid peptide that elicits mouse T cell responses when presented by cells expressing syngeneic Ad or Ab class II MHC molecules. We previously showed that both the unfolding of this peptide by APC and the integrity of its N terminus segment were required for efficient apamin T cell recognition. To seek further information on the sites through which this peptide interacts with Ia and/or TCR, we used a panel of Ad- or Ab-restricted, apamin-specific THC to probe the antigenicity of a series of synthetic apamin analogs. These included peptides either truncated at the N terminus, or substituted by Ala at position 2, 4, 6, 7, 8, or 10. Analysis of THC responses to apamin analogs and use of the latter in competition assays for peptide presentation revealed the following: 1) optimal apamin T cell recognition critically involved Lys4, Ala5, Pro6, Glu7, and Leu10. The role of these residues in either "Ia or TCR binding regions" was found to depend upon the restricting Ia molecules at play. Thus, Lys4, Glu7, and Leu10 were TCR-binding residues in both Ad- and Ab-apamin complexes, whereas Lys4 participated in apamin/Ab but not, or to a marginal extent, in apamin/Ad interaction. Furthermore, Pro6 was associated either with an Ia contact region or a TCR interaction site when apamin was presented by Ab or Ad molecules, respectively. Unfolded apamin and the unrelated chicken OVA323-339 peptide were found to bind to the same, or closely related site(s) of Ad, as shown by their ability to compete reciprocally for recognition by appropriate Ad-restricted THC. Four distinct TCR V beta genes (V beta 2, V beta 4, V beta 6, and V beta 8) were found to be used in our panel of 16 apamin-specific THC. These data indicate that apamin interacts with Ad or TCR through a motif resembling other beta-sheeted, Ad-binding sequences; however, based on the spacing of the critical residues (i.e., 4, 7, and 10), the possibility exists that apamin processing permits the folding of this sequence into an alpha-helix.
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PMID:Structural analysis of the interaction of apamin with Ia and its recognition by Ad- or Ab-restricted mouse T cells. 247 20

Three synthetic peptides, EEYEYE (peptide 1), EEYEYEEEYEYE (peptide 2), and YEEEEY (peptide 3), were tested for their ability to induce common Id that had been previously characterized for murine antibodies specific to random synthetic polymers of glutamic acid, alanine, and tyrosine ((Glu,Ala,Tyr)n) (cGAT Id). Protein conjugates of either peptide 2 or peptide 3, but not peptide 1, induced cGAT Id. This unique approach directly identified two peptides capable of inducing cGAT Id antibodies. Previous immunization with peptide 1-protein conjugate inhibited the cGAT Id response to peptide 2 conjugated to a different protein carrier. Thus, a neighboring or overlapping epitope can be used to inhibit a cGAT Id-inducing epitope without the participation of carrier-specific Ts and without using anti-Id antibodies. In contrast, previous immunization with peptide 1-protein conjugate did not inhibit cGAT Id induction by peptide 3-protein conjugate or by (Glu,Ala,Tyr)n. This ruled out the participation of Id-specific Ts cells. The effectiveness of inhibition coincided with the avid binding of anti-peptide 1 antibodies to peptide 2, which was > 10 and 100 times stronger than the binding to peptide 3 and (Glu,Ala,Tyr)n, respectively. We hypothesize that the primed peptide 1-specific B cells capture and process peptide 2-protein efficiently and act as APC to Th cells specific to the protein of the challenging Ag, resulting in the selective and dominant activation of peptide 1-specific B cells. Thus, our data suggest that epitope priming can inhibit an Id response to a neighboring epitope by a mechanism of clonal dominance.
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PMID:The B cell immune response to an idiotype-inducing peptide epitope can be inhibited by immunodominance of a neighboring epitope. 768 Oct 77

Mutation of the p53 gene is thought to be a late event in human colorectal carcinogenesis, involved in the malignant conversion of the adenoma to the carcinoma. One of the questions that we hoped to address was whether, in vivo, a single mutational event in one p53 gene is sufficient to confer a significant growth advantage on a colonic epithelial cell. Such a growth advantage could result either from an increase in growth rate and/or loss of response to inhibitory growth signals naturally present in the colonic crypt. We therefore introduced the pC53-SCX3 143 (Val-Ala) p53 mutation into a non tumorigenic adenoma derived cell line, AA/C1, which contained a truncating APC mutation, activating K-ras mutation but was wild-type for the p53 protein. High levels of mutant p53 protein were detected in the pC53-SCX3 transfected AA/C1 cell lines but was found not to affect either the in vitro (colony forming efficiency, anchorage independence) or in vivo (tumorigenicity in nude mice) growth, when compared to vector control or the parental AA/C1 cell line. In addition, to test whether the cells become less sensitive to inhibitory growth factors, the response of the cell lines to the naturally occurring growth inhibitor TGF beta was also investigated. Even though TGF beta had previously been implicated in the control of growth of intestinal epithelium, expression of the mutant p53 protein did not affect the sensitivity of the parental AA/C1 cell line to TGF beta. Under the experimental conditions tested expression of the 143 (Val-Ala) p53 protein was unable to affect the in vitro or in vivo growth characteristics of the adenoma derived AA/C1 cell line. When compared to other studies, these results suggest that the genetic background of the individual recipient cell may greatly influence the effect of expression of a particular p53 mutation.
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PMID:Transfection and expression of mutant p53 protein does not alter the in vivo or in vitro growth characteristics of the AA/C1 human adenoma derived cell line, including sensitivity to transforming growth factor-beta 1. 815 11

Carbohydrates are T cell independent antigens because they do not bind to MHC molecules. However, glycopeptides might potentially bind to MHC molecules via their peptide component for presentation to T cells. We have conjugated the disaccharide galabiose [Gal alpha (1-4)Gal beta] to the amino terminus of a T cell peptide determinant from hen egg-white lysozyme [HEL(52-61)]. The resulting glycopeptide (Gal2-52-61) and a nonglycosylated analogue containing tyrosine and glutamic acid at the amino-terminus (YE-52-61) bound equally well to purified I-Ak. T cell hybridomas were produced after immunization with Gal2-52-61. Many of the T cell hybridomas were glycopeptide-specific and responded to Gal2-52-61 but not to nonglycosylated synthetic peptides or to HEL presented by APC, indicating that the carbohydrate moiety influenced T cell recognition. Recognition was lost with the amino terminal attachment of the disaccharide to a peptide six amino acids longer at the amino terminus than HEL(52-61). Recognition also was lost with peptides containing only a single galactosyl residue or with galabiose bound to a different I-Ak binding peptide. T cells directed to Gal2-52-61 recognized glycopeptides having significant variation in the disaccharide structure, such as HEL(52-61) glycopeptides carrying lactose, cellobiose, or hepta-o-acetylated galabiose. Peptide residues were important features of the T cell epitope; Ala substitutions of two critical T cell contact residues of HEL(52-61) (Tyr53 and Leu56) abrogated T cell reactivity to the glycopeptides without affecting binding to I-Ak. In conclusion, we propose that these T cells recognize a peptide conformation specific to glycopeptide-I-Ak complexes and that this recognition does not involve specific interaction between the carbohydrate moiety and the T cell receptor.
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PMID:Glycopeptides bind MHC molecules and elicit specific T cell responses. 836 Apr 71

The proteolytic cleavage and subsequent inactivation of recombinant human factor VIII (rhFVIII) and human factor VIIIa (rhFVIIIa) by recombinant human activated protein C (rAPC) was analyzed in the presence and absence of human protein S and human factor V (FV). Membrane-bound rhFVIIIa spontaneously looses most of its initial cofactor activity after 15 minutes of incubation at pH 7.4. The remaining activity can be eliminated after incubation with rAPC. Complete inactivation of the membrane-bound rhFVIII and rhFVIIIa by APC correlates with cleavage at Arg336. The inactivation of rhFVIII and human plasma FV by rAPC were also compared. Under similar experimental conditions, complete inactivation of membrane-bound FVIII (60 nmol/L) by rAPC (10 nmol/L) requires 4 hours of incubation, in contrast to 5 minutes for FV (60 nmol/L). The presence of protein S (100 nmol/L) enhances rhFVIII inactivation by rAPC by 6.4-fold and FVa inactivation by twofold, whereas membrane-bound FV showed no protein S dependence during inactivation. The addition of human FV to the APC/protein S inactivation mixture increases by approximately twofold the rate of inactivation of rhFVIII. The effect of FV on the rhFVIII inactivation by APC is protein S-dependent, because FV alone has no effect on the inactivation rate of rhFVIII by APC. Western blotting using a monoclonal antibody that recognizes an epitope between amino acid residues 307 and 506 of human FV showed that FV was completely cleaved by APC at the beginning of the rhFVIII inactivation process. These data suggest that FV fragments derived from the B region of the procofactor after incubation of the membrane-bound procofactor with APC, but not intact single-chain FV, stimulate APC activity in the presence of protein S. rhFVIII, FV, and rhFVIIIa were not inactivated by Glu20-->Ala-substituted rAPC (rAPCgamma20A), and membrane-bound factor Va was only partially inactivated. Our data suggest that (1) FV and FVa are the physiologically significant substrates for APC inactivation and (2) membranes-bound APC-treated FV is a cofactor for the APC inactivation of rhFVIII only in the presence of the intact form of protein S.
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PMID:Comparison of activated protein C/protein S-mediated inactivation of human factor VIII and factor V. 863 40

Residues 46 and 54 on pigeon cytochrome c 43-58 (p43-58) analogues function as agretopes (sites bound to MHC molecules). Phenylalanine (F) and alanine (A) at positions 46 and 54 on p43-58 respectively bind to I-Ab. Aspartic acid (D) and alanine at positions 46 and 54 respectively bind to I-Ak. To determine the allele specific binding sites (desetope (s)) on class II molecules that are correspondent to the agretopes of peptide antigen (Ag), we analyzed directly binding capacity of p43-58 analogues with glutamic acid (E) at the epitopic position 50 (50E) to L cell transfectants expressing recombinant I-A molecules between b and k types. An Ak binding peptide, 46D50E54A, bound to transfectant possessing amino acid sequence of k type on N-terminal half of alpha-helix of A alpha-chain irrespective of the b type sequence on the other part, whereas an Ab binding peptide, 46F50E54A, did not bind to these transfects. Thus, agretopic residue 46 of 46D50E54A peptides appeared to bind to N-terminal half of alpha-helix of A alpha-chain. To define critical residues for the allele specific peptide binding, we then analyzed peptide binding capacity of Ak mutants substituted one of four polymorphic residues between Ak and Ab molecules. An Ak mutant, Ak alpha(56A), where arginine (R) at position 56 of the Ak alpha-chains was substituted with alanine located at the same position 56 of the Ab alpha-chains hardly bound 46D50E54A. By contrast, the Ak alpha(56A) bound 46F50E54A. Furthermore, Ak restricted T cell hybridomas responded to 46F50E54A but not to 46D50E54A in the presence of the Ak alpha(56A) APC. Thus, an amino acid on the position 56 of A alpha-chain determines critically specificity of the allele specific peptide binding (desetope).
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PMID:[Analysis of the allele specific Ag-binding site on murine class II MHC]. 864 75

T cell adhesion induced after physiological stimulation by antigen was investigated using murine T cell hybridomas specific for a tetanus toxin peptide. By employing a novel assay, the T cell hybridomas were shown to strongly adhere to peptide-pulsed APC in a dose-dependent fashion. Adhesion peaked at 30-60 min and declined thereafter. This assay allowed us to study the relationship between T cell adhesion and later activation responses using tetanus toxin peptide and alanine monosubstituted analogs. We show that the degree of peptide-induced T cell adhesion correlated with the magnitude of late functional responses. CD4, LFA-1 (CD11a/CD18), and CD28 were critical in the adhesion response. The enhancing role of CD4 was further demonstrated by reduced levels of T cell adhesion and late responses of CD4- T cell hybridomas. Reexpression of CD4 reversed these defects. Our data suggest a link between antigen-induced T cell adhesion and late responses and also suggest that signals mediated by TCR and CD4 coengagement may induce a greater activation and/or recruitment of molecules involved in T cell adhesion.
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PMID:Induction of T cell adhesion by antigen stimulation and modulation by the coreceptor CD4. 891 73


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