Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Peptides that bind with high affinity to class II MHC molecules can inhibit T cell activation both in vitro and in vivo. Thus, they have been suggested as potential therapeutic agents for MHC-associated autoimmune diseases. We have constructed nonnatural peptides with high affinity for certain disease-associated MHC alleles. More specifically, a particular peptide, designated as CY-760.50, was found to have a high binding affinity for DR1, slow dissociation kinetics after binding to MHC, and prolonged stability in human serum. However, when the ability of this peptide to block peptide presentation to an influenza hemagglutinin 307-319 peptide-specific, DR1-restricted T cell clone was examined, it was found that MHC blockade could only be achieved when high concentrations of peptide were present along with Ag in the fluid phase. Thus, pretreatment of APC with MHC class II blocker, followed by removal of unbound blocker, did not result in saturation of MHC molecules, because practically immediate reacquisition of Ag-presenting capacity was observed after removal of fluid phase blocker. The pharmacokinetic behavior and the duration of blocking activity of CY-760.50 were also examined in vivo, taking advantage of the fact that the mouse MHC class II molecule I-Ab also bound CY-760.50 with high affinity. CY-760.50 administered i.v. to C57BL/6 mice was rapidly cleared from the circulation and virtually undetectable in the serum 10 min after injection. This fast clearance rate was paralleled by a similarly short duration of the MHC blockade effect. These in vivo results have implications concerning the biology of peptide-MHC interactions, and suggest that MHC blockade may not be feasible as a therapeutic approach unless effective concentrations of inhibitor can be maintained over extended periods of time in the extracellular fluids.
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PMID:Failure to demonstrate long-lived MHC saturation both in vitro and in vivo. Implications for therapeutic potential of MHC-blocking peptides. 815 54

We have investigated the ability of APC Class II molecules to bind and release exogenous peptides, two phenomena that are still poorly understood. In order to investigate the half-life of the complex of an exogenous peptide with DR molecules we have evaluated the uptake and release of the radiolabeled peptide 17-29-Tyr of influenza virus matrix protein (MA 17-29-Y) by a B-EBV cell line at different times and under different conditions. We have found that the kinetics of both binding and release of the peptide are very fast in living cells; using glutaraldehyde-fixed cells, the kinetics of the two phenomena are slow, closely resembling those observed with the same peptide and purified, immobilized DR molecules. As confirmed by the study of a specific T-cell clone activation, the Class II-MA 17-29-Y complexes are short-living ones, with an average half-life of 55 min, and the DR molecules that bind exogenous peptides continuously undergo peptidic exchange. These data, taken together, suggest that the APC are endowed with cellular mechanisms that increase the efficiency of both the loading and the unloading of Class II HLA with exogenous peptides. These mechanisms do not appear to require ATP or to involve newly synthesized Class II molecules, intracellular acidic compartments, or the microtubule-microfilament system. On the other hand, an undamaged cell membrane appears to be crucial for an efficient binding.
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PMID:Cellular mechanisms of exogenous peptide binding to HLA class II molecules in B cells. 816 38

The natural Ag influenza virus A was used to test the requirements for the HLA-DR1-restricted presentation of the epitopes 18-29 in the matrix protein and 307-318 in the hemagglutinin protein. CD4+ cytotoxic T cell clones of similar efficiency were used to detect presentation of these two epitopes. Presentation of the matrix epitope by APC pulsed with either inactivated virus particles or purified soluble protein followed the classical pathway in that 1) it required invariant chain expression, 2) it was blocked by inhibition of protein synthesis, and 3) it was dependent on a function(s) encoded in the MHC class II region. These characteristics suggest that peptides corresponding to the matrix epitope can only load onto newly synthesized class II molecules that were targeted to a processing compartment by the invariant chain. In contrast, presentation of the hemagglutinin epitope processed from virus particles followed a different pathway. First, presentation of hemagglutinin was independent of invariant chain expression. Second, a human B lymphoblastoid cell line in which protein synthesis was inhibited for 9 h was still able to present hemagglutinin even at very low doses of Ag. Third, a DR1-transfected mutant B cell line missing the MHC class II region was able to present hemagglutinin. Thus, mature class II alpha beta molecules can acquire immunogenic peptides derived from intact natural Ags for presentation to CD4+ T cells. This pathway may be useful for the binding of peptides derived from Ags that are rapidly degraded upon uptake into APC.
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PMID:Two processing pathways for the MHC class II-restricted presentation of exogenous influenza virus antigen. 817 8

To assess interactions between T cells and APC in patients with SLE, PBL were stimulated in vitro and IL-2 production measured after stimulation with either a MHC-self-restricted Ag (influenza A virus) or an Ag which can use both MHC-self-restricted or unrestricted T cell activation pathways (HLA-alloantigen). SLE patients (n = 26) and controls (n = 8) were categorized as responder (+) or nonresponder (-) for each stimulus and grouped according to their paired response pattern. All controls responded to both influenza virus (Flu) or alloantigen (Allo) and were categorized as +/+. In contrast, SLE patient response patterns were heterogeneous with no evidence for a single SLE-associated defect. Instead, SLE patient responses fell into one of three different patterns: a) normal responses to both Flu and Allo (+/+), observed in nine (35%) patients; b) defective responses to Flu but intact Allo responses (-/+) observed in 12 (46%) SLE patients; and c) defective responses to both Flu and Allo (-/-), observed in five (19%) SLE patients. There was no statistically significant correlation between immune response pattern and the use of immunosuppressants. Further analysis of -/- SLE patients indicated defects in APC function and in both CD4+ and CD8+ T cell function. In contrast, cell depletion and add-back studies in -/+ SLE patients demonstrated defects in APC function only. Thus, similar to the well recognized clinical heterogeneity among SLE patients, our data support the concept that SLE patients are heterogeneous with respect to in vitro T cell-APC function, exhibiting responses ranging from normal function to defects in APC and in both T cell subsets. Prospective studies are in progress to determine the clinical relevance of these observations.
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PMID:T cell-antigen-presenting cell interactions in human systemic lupus erythematosus. Evidence for heterogeneous expression of multiple defects. 837 10

Peptide fragments are displayed on the APC surface by MHC class I molecules as ligands for appropriate TCR. Sequence analysis of MHC-bound peptide mixtures has suggested that naturally processed peptides are defined by their length and by the presence of MHC allele-defined consensus motifs. To define the minimal OVA peptide presented by Kb MHC, and the requirements for generation of endogenous OVA/Kb complex, APC were transfected with OVA cDNA constructs. We show that optimal stimulation of OVA/Kb-specific B3Z T cell hybrid by Kb-APC requires the OVA257-264 peptide (SIINFEKL, SL8) whether added exogenously, or when synthesized endogenously as precursor polypeptides. Thus, all information necessary for expression of the OVA/Kb complex is contained within the Kb octapeptide motif shared by SL8. Unexpectedly, the SL8/Kb or the influenza NP/Db complexes were also generated in APC even when the peptide coding sequences were placed in incorrect translational reading frames. By contrast, identical manipulations of the translational reading frame of the lacZ reporter gene reduced protein synthesis to undetectable levels demonstrating the remarkable efficiency with which endogenous peptide/MHC are generated in and presented by APC to T cells. These characteristics of the endogenous presentation may explain how large numbers of distinct peptide/MHC complexes are displayed on the cell surface and surveyed by TCR.
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PMID:Endogenous generation and presentation of the ovalbumin peptide/Kb complex to T cells. 845 52

The capacity of adjuvants to stimulate cytokine production by APC is important for the initiation of the immune response. Novel adjuvant formulations based on the iscom technology have been developed using selected triterpenoid components from Quillaja saponaria Molina. Five of these new Quillaja formulations were used to prepare matrix (an antigen-free particle) and tested for their capacity to stimulate IL-1 secretion by murine peritoneal cells in vitro. The formulation denominated QH 7.0.3 was superior to the other matrix formulations, including the original spikoside matrix. The QH 7.0.3 formulation in iscoms containing influenza virus envelope antigens induced IL-1 secretion more efficiently than the antigen-free matrix, or a mixture of matrix and viral antigens, or the free Quillaja components of similar composition. Compared with adjuvants known as IL-1 inducers, QH 7.0.3 flu-iscoms were as efficient as the most prominent IL-1 inducer, i.e. lipopolysaccharide (LPS) and superior to cholera toxin (CT) and muramyl dipeptide (MDP). These results indicate that the composition per se of triterpenoids included in iscoms or matrix has a prominent influence on the level of APC activation which may result in qualitatively different immune responses in vivo.
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PMID:In vitro activation of antigen-presenting cells (APC) by defined composition of Quillaja saponaria Molina triterpenoids. 869 31

Proteolysis of endogenously synthesized cellular proteins is essential for constitutive display of processed peptide/MHC class I complexes on the APC surface for stimulating CD8+ T cells. However, the extent to which normal protein turnover serves as the source of processed peptides is not clear. To address this question, we used pairs of novel N-end rule substrates that varied in their intracellular stability and served as precursors for generating peptide/MHC class I (OVA257-264/Kb or influenza nucleoprotein 366-374/Db) complexes. Surprisingly, although each of three precursor pairs tested varied profoundly in their intracellular stability, they were indistinguishable in either T cell stimulation assays, or in the amounts of naturally processed peptides in the APC extracts. Our findings demonstrate that the proteolytic turnover of endogenously synthesized proteins is not directly proportional to the generation of processed antigenic peptide/MHC class I complexes.
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PMID:Generation of naturally processed peptide/MHC class I complexes is independent of the stability of endogenously synthesized precursors. 875 7

We report that I-Ab-restricted T cell clones, elicited by influenza infection of C57BL/10 mice and specific for the hemagglutinin peptide HA1 186-205, express class II. They respond to peptide stimulation by IL release (IL-3 or IFN-gamma) without a requirement for APC but do not proliferate. Moreover, surface expression of class II requires de novo synthesis in the presence of the stimulatory peptide and is inhibited by coculture with TCR-specific Ab, or brefeldin A or cycloheximide. Clonotypic specificity of peptide induction was confirmed by failure of other allele specific peptides to enhance class II expression. Addition of the viral peptide to T cells induced homotypic adhesion, which provides a physical basis for stabilization of class II-peptide complexes at the cell surface. Extinction of class II expression was evident in the corresponding T cell hybridomas, which might account for the failure to report class II expression by murine T cells. Control studies indicated that class II was not passively acquired from APC by demonstrating 1) failure of processed Ag to induce class II expression, 2) allo-class II (Ak) was not acquired by coculture with peptide and semisyngeneic (H-2 b/k) APC, 3) absence of class II expression by a NP peptide-specific Th2 clone under identical culture conditions, and most significantly, 4) reverse-transcriptase PCR amplification and surface expression of class II using highly purified preparations of FACS-selected CD4+ class II- cells cocultured with the stimulatory peptide.
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PMID:Viral peptide specific induction of MHC class II expression by murine T cell clones. 880 37

We have investigated an improved method for generating sizable numbers of mature dendritic cells from nonproliferating progenitors in human blood. The procedure uses 1% human plasma in the place of 10% fetal calf serum and involves two steps. The first step or 'priming' phase is a 6-7 day culture of T cell depleted mononuclear cells in medium supplemented with GM-CSF and IL-4. The second step or 'differentiation' phase requires the exposure to macrophage conditioned medium. This medium cannot be replaced by several known cytokines such as TNF-alpha, IL-1, IL-6, IL-12 and IL-15, and cannot be inhibited with neutralizing antibodies to IL-1, TNF-alpha, IL-6 or IL-12 alone, or in combination. Using this two-step approach, we obtain substantial yields. About 1-3 x 10(6) mature dendritic cells are generated from 40 ml of blood vs. < 0.1 x 10(6) from noncytokine treated blood. The dendritic cells derive from progenitors found primarily in a radioresistant population of CD14+ and adherent blood mononuclear cells and have all the features of mature cells. They include a stellate cell shape, nonadherence to plastic, and very strong T cell stimulatory activity. Strong APC function was evident for both the proliferation of allogeneic T cells in the MLR, and the generation by syngeneic T cells of class I restricted, CTL responses to influenza virus. A panel of dendritic cell restricted markers is also expressed, including CD83, p55, and perinuclear CD68. All of these dendritic cell properties are retained for at least 3 days when the cytokines are removed, suggesting that these populations are stable and terminally differentiated. We suggest that these cells will be effective in vivo as adjuvants for active immunotherapy.
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PMID:Improved methods for the generation of dendritic cells from nonproliferating progenitors in human blood. 884 51

We had previously shown that a genetically engineered Ig expressing an immunodominant CD4+ T epitope corresponding to the 110-120 amino acids of influenza virus hemagglutinin (HA), activated T cells more efficiently than the synthetic peptide. Taking advantage of a T cell hybridoma specific for HA 110-120 and transfected with a reporter gene under the IL-2 promoter, we studied the kinetics of generation and persistence on surface MHC-II of the HA 110-120 peptide derived from various carriers. Our results show that the generation rate of immunogenic MHC II-peptide complex is dependent on the nature of the carrier. Abs specific for HA 110-120 peptide or for other epitopes on HA affect through various mechanisms the presentation of HA 110-120 peptide to T cells. The persistence of immunogenic MHC II-peptide complex on the surface of APC is not dependent on the nature of the carrier and correlates with the half-life of class II molecules, suggesting an irreversible binding of peptides to MHC-II molecules in 2PK3 murine B lymphoma cells.
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PMID:Kinetics of generation and persistence on membrane class II molecules of a viral peptide expressed on foreign and self proteins. 887 42


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