Hybrids of dendritic cells and tumor cells generated by electrofusion simultaneously present immunodominant epitopes from multiple human tumor-associated antigens in the context of MHC class I and class II molecules

Hybrid cells generated by fusing dendritic cells with tumor cells (DC-TC) are currently being evaluated as cancer vaccines in preclinical models and human immunization trials. In this study, we evaluated the production of human DC-TC hybrids using an electrofusion protocol previously defined for murine cells. Human DCs were electrically fused with allogeneic melanoma cells (888mel) and were subsequently analyzed for coexpression of unique DC and TC markers using FACS and fluorescence microscopy. Dually fluorescent cells were clearly observed using both techniques after staining with Abs against distinct surface molecules suggesting that true cell fusion had occurred. We also evaluated the ability of human DC-TC hybrids to present tumor-associated epitopes in the context of both MHC class I and class II molecules. Allogeneic DCs expressing HLA-A*0201, HLA-DR beta 1*0401, and HLA-DR beta 1*0701 were fused with 888mel cells that do not express any of these MHC molecules, but do express multiple melanoma-associated Ags. DC-888mel hybrids efficiently presented HLA-A*0201-restricted epitopes from the melanoma Ags MART-1, gp100, tyrosinase, and tyrosinase-related protein 2 as evaluated by specific cytokine secretion from six distinct CTL lines. In contrast, DCs could not cross-present MHC class I-restricted epitopes after exogenously loading with gp100 protein. DC-888mel hybrids also presented HLA-DR beta 1*0401- and HLA-DR beta 1*0701-restricted peptides from gp100 to CD4(+) T cell populations. Therefore, fusions of DCs and tumor cells express both MHC class I- and class II-restricted tumor-associated epitopes and may be useful for the induction of tumor-reactive CD8(+) and CD4(+) T cells in vitro and in human vaccination trials.     

Rapid responses to high temperature and desiccation but not to low temperature in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera,Tineidae)

A broad definition of rapid cold hardening (RCH) is that it is the process whereby insects increase their survival of a sub-zero temperature after a brief (h) pre-exposure to a less severe low temperature. The effects of various pre-treatments on survival of two h at -7.9 degrees C were investigated in the freeze tolerant sub-Antarctic caterpillar Pringleophaga marioni (Lepidoptera: Tineidae), the first time RCH has been investigated in a freeze tolerant arthropod. All caterpillars froze when exposed to -7.9 degrees C, and none of the low temperature pre-treatments (-5, 0, 5 and 15 degrees C, as well as -5 degrees C and 0 degrees C with a delay before freezing) nor slow cooling (0.1 degrees C/min) elicited any improvement in survival of -7.9 degrees C as compared to controls. However, high temperature treatments (25, 30 and 35 degrees C), desiccation and acclimation for 5 days at 0 degrees C did result in significant increases in survival of the test temperature, possibly as a result of heat shock protein production. Haemolymph osmolality was elevated only by the 35 degrees C pre-treatment. It is suggested that the unpredictable environment of Marion Island means that P. marioni must always be physiologically prepared to survive cold snaps, and that this year-round cold hardiness therefore supersedes a rapid cold hardening response.     

Glycosphingolipids of the model fungus Aspergillus nidulans: characterization of GIPCs with oligo-alpha-mannose-type glycans

Aspergillus nidulans is a well-established nonpathogenic laboratory model for the opportunistic mycopathogen, A. fumigatus. Some recent studies have focused on possible functional roles of glycosphingolipids (GSLs) in these fungi. It has been demonstrated that biosynthesis of glycosylinositol phosphorylceramides (GIPCs) is required for normal cell cycle progression and polarized growth in A. nidulans (Cheng, J., T.-S. Park, A. S. Fischl, and X. S. Ye. 2001. Mol. Cell Biol. 21: 6198-6209); however, the structures of A. nidulans GIPCs were not addressed in that study, nor were the functional significance of individual structural variants and the downstream steps in their biosynthesis. To initiate such studies, acidic GSL components (designated An-2, -3, and -5) were isolated from A. nidulans and subjected to structural characterization by a combination of one-dimensional (1-D) and 2-D NMR spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), ESI-MS/collision-induced decomposition-MS (MS/CID-MS), ESI-pseudo-[CID-MS]2, and gas chromatography-MS methods. All three were determined to be GIPCs, with mannose as the only monosaccharide present in the headgroup glycans; An-2 and An-3 were identified as di- and trimannosyl inositol phosphorylceramides (IPCs) with the structures Man alpha 1-->3Man alpha 1-->2Ins1-P-1Cer and Man alpha 1-->3(Man alpha 1-->6)Man alpha 1-->2Ins1-P-1Cer, respectively (where Ins = myo-inositol, P = phosphodiester, and Cer = ceramide). An-5 was partially characterized, and is proposed to be a pentamannosyl IPC, based on the trimannosyl core structure of An-3.     

Structure and function of an archaeal homolog of survival protein E (SurEalpha): an acid phosphatase with purine nucleotide specificity

The survival protein E (SurE) family was discovered by its correlation to stationary phase survival of Escherichia coli and various repair proteins involved in sustaining this and other stress-response phenotypes. In order to better understand this ancient and well-conserved protein family, we have determined the 2.0A resolution crystal structure of SurEalpha from the hyperthermophilic crenarchaeon Pyrobaculum aerophilum (Pae). This first structure of an archaeal SurE reveals significant similarities to and differences from the only other known SurE structure, that from the eubacterium Thermatoga maritima (Tma). Both SurE monomers adopt similar folds; however, unlike the Tma SurE dimer, crystalline Pae SurEalpha is predominantly non-domain swapped. Comparative structural analyses of Tma and Pae SurE suggest conformationally variant regions, such as a hinge loop that may be involved in domain swapping. The putative SurE active site is highly conserved, and implies a model for SurE bound to a potential substrate, guanosine-5'-monophosphate (GMP). Pae SurEalpha has optimal acid phosphatase activity at temperatures above 90 degrees C, and is less specific than Tma SurE in terms of metal ion requirements. Substrate specificity also differs between Pae and Tma SurE, with a more specific recognition of purine nucleotides by the archaeal enzyme. Analyses of the sequences, phylogenetic distribution, and genomic organization of the SurE family reveal examples of genomes encoding multiple surE genes, and suggest that SurE homologs constitute a broad family of enzymes with phosphatase-like activities.     

Exploration of the transition state for tertiary structure formation between an RNA helix and a large structured RNA

Docking of the P1 duplex into the pre-folded core of the Tetrahymena group I ribozyme exemplifies the formation of tertiary interactions in the context of a complex, structured RNA. We have applied Phi-analysis to P1 docking, which compares the effects of modifications on the rate constant for docking (k(dock)) with the effects on the docking equilibrium (K(dock)). To accomplish this we used a single molecule fluorescence resonance energy transfer assay that allows direct determination of the rate constants for formation of thermodynamically favorable, as well as unfavorable, states. Modification of the eight groups of the P1 duplex that make tertiary interactions with the core and changes in solution conditions decrease K(dock) up to 500-fold, whereas k(dock) changes by 相似文献   

Direct phenotypic analysis of human MHC class I antigen presentation: visualization,quantitation, and in situ detection of human viral epitopes using peptide-specific,MHC-restricted human recombinant antibodies

The advent in recent years of the application of tetrameric arrays of class I peptide-MHC complexes now enables us to detect and study rare populations of Ag-specific CD8(+) T cells. However, available methods cannot visualize or determine the number and distribution of these TCR ligands on individual cells nor detect APCs in tissues. In this study, we describe for the first time studies of human class I peptide-MHC ligand presentation. These studies were facilitated by applying novel tools in the form of peptide-specific, HLA-A2-restricted human recombinant Abs directed toward a viral epitope derived from human T cell lymphotropic virus type I. Using a large human Ab phage display library, we isolated a large panel of recombinant Fab Abs that are specific for a particular peptide-MHC class I complex in a peptide-dependent, MHC-restricted manner. We used these Abs to visualize the specific complex on APCs and virus-infected cells by flow cytometry, to quantify the number of, and visualize in situ, a particular complex on the surface of APCs bearing complexes formed by naturally occurring active intracellular processing of the cognate viral Ag. These findings demonstrate our ability to transform the unique fine specificity, but low intrinsic affinity of TCRs into high affinity soluble Ab molecules endowed with a TCR-like specificity toward human viral epitopes. These molecules may prove to be crucial useful tools for studying MHC class I Ag presentation in health and disease as well as for therapeutic purposes in cancer, infectious diseases, and autoimmune disorders.     

Estimating hypermutation rates from clonal tree data

To understand the mechanisms underlying the varying patterns of mutations that occur during immune and autoimmune responses, estimates of the somatic hypermutation rate are critical. However, despite its significance, precise estimates of the mutation rate do not currently exist. Microdissection studies of mutating B cell clones provide an opportunity to measure this rate more accurately than previously possible. Each microdissection provides a number of clonally related sequences that, through the analysis of shared mutations, can be genealogically related to each other. The shape of these clonal trees is influenced by many processes, including the hypermutation rate. We have developed two different methods to estimate the mutation rate based on these data. These methods are applied to two sets of experimental data, one from an autoimmune response and one from the antihapten response to (4-hydroxy-3-nitrophenyl)acetyl (NP). Comparable mutation rates are estimated for both responses, 0.7-0.9 x 10(-3) and 0.9-1.1 x 10(-3) bp(-1) division(-1) for the autoimmune and NP responses, respectively. In addition to comparing the results of the two procedures, we investigate the effect on our estimate of assumptions, such as the fraction of lethal mutations.     

Lipid raft distribution of CD4 depends on its palmitoylation and association with Lck,and evidence for CD4-induced lipid raft aggregation as an additional mechanism to enhance CD3 signaling

By mutagenesis, we demonstrated that the palmitoylation of the membrane-proximal Cys(396) and Cys(399)of CD4, and the association of CD4 with Lck contribute to the enrichment of CD4 in lipid rafts. Ab cross-linking of CD4 induces an extensive membrane patching on the T cell surface, which is related to lipid raft aggregation. The lipid raft localization of CD4 is critical for CD4 to induce the aggregation of lipid rafts. The localization of CD4 in lipid rafts also correlates to the ability of CD4 to enhance receptor tyrosine phosphorylation. Thus, our data suggest that CD4-induced aggregation of lipid rafts may play an additional role in CD4 signaling besides its adhesion to MHC molecules and association with Lck.     

An inclusion membrane protein from Chlamydia trachomatis enters the MHC class I pathway and stimulates a CD8+ T cell response

During its developmental cycle, the intracellular bacterial pathogen Chlamydia trachomatis remains confined within a protective vacuole known as an inclusion. Nevertheless, CD8(+) T cells that recognize Chlamydia Ags in the context of MHC class I molecules are primed during infection. MHC class I-restricted presentation of these Ags suggests that these proteins or domains from them have access to the host cell cytoplasm. Chlamydia products with access to the host cell cytoplasm define a subset of molecules uniquely positioned to interface with the intracellular environment during the pathogen's developmental cycle. In addition to their use as candidate Ags for stimulating CD8(+) T cells, these proteins represent novel candidates for therapeutic intervention of infection. In this study, we use C. trachomatis-specific murine T cells and an expression-cloning strategy to show that CT442 from Chlamydia is targeted by CD8(+) T cells. CT442, also known as CrpA, is a 15-kDa protein of undefined function that has previously been shown to be associated with the Chlamydia inclusion membrane. We show that: 1) CD8(+) T cells specific for an H-2D(b)-restricted epitope from CrpA are elicited at a significant level (approximately 4% of splenic CD8(+) T cells) in mice in response to infection; 2) the response to this epitope correlates with clearance of the organism from infected mice; and 3) immunization with recombinant vaccinia virus expressing CrpA elicits partial protective immunity to subsequent i.v. challenge with C. trachomatis.