HLA-B27-restricted antigen presentation in the absence of tapasin reveals polymorphism in mechanisms of HLA class I peptide loading

Tapasin is a resident ER protein believed to be critical for antigen presentation by HLA class I molecules. We demonstrate that allelic variation in MHC class I molecules influences their dependence on tapasin for peptide loading and antigen presentation. HLA-B*2705 molecules achieve high levels of surface expression and present specific viral peptides in the absence of tapasin. In contrast, HLA-B*4402 molecules are highly dependent upon human tapasin for these functions, while HLA-B8 molecules are intermediate in this regard. Significantly, HLA-B*2705 like HLA-B*4402, requires tapasin to associate efficiently with TAP (transporters associated with antigen processing). The unusual ability of HLA-B*2705 to form peptide complexes without associating with TAP or tapasin confers flexibility in the repertoire of peptides presented by this molecule. We speculate that these properties might contribute to the role of HLA-B27 in conferring susceptibility to inflammatory spondyloarthropathies.     

A single nonamer from the Yersinia 60-kDa heat shock protein is the target of HLA-B27-restricted CTL response in Yersinia-induced reactive arthritis

The reason for the high association of HLA-B27 with diseases such as ankylosing spondylitis and reactive arthritis is not clear. In reactive arthritis, the triggering bacteria are known, thus allowing investigation of their interaction with HLA-B27. CTL lines derived from five patients with Yersinia-induced reactive arthritis were raised by repeated stimulation in vitro with either Yersinia-infected autologous macrophages (four patients) or pooled peptides (three patients) having the HLA-B27-binding motif. The peptides were derived from five Yersinia proteins and from the chlamydial 57-kDa heat shock protein (hsp). Cytotoxicity of T cell lines was then tested against these peptides. Lytic activity was obtained with T cells stimulated with viable Yersinia or pooled peptides. Targets successfully used for lysis were cells pulsed with peptides from the Yersinia 60-kDa hsp, but not cells pulsed with peptides from other Yersinia proteins or the chlamydial hsp. T cell lines raised with 60-kDa peptides also lysed targets infected with Yersinia. Most interestingly, all three CTL lines tested (one raised with Yersinia; two with pool of peptides) recognized only one single peptide (321-329) of seven tested from the Yersinia hsp60. Cytotoxicity occurred only when target cells were matched for HLA-B27. This identification of an immunogenic peptide derived from an arthritogenic bacterium and presented by HLA-B27 opens the way for future investigation of the role of T cells specific for this peptide or cross-reacting peptides, in the immunopathology of HLA-B27-associated diseases.     

Junctional diversity in the absence of N regions. Neonatal T cell receptor beta chain junctional sequences are more heterogeneous than neonatal T cell receptor gamma delta or IgH junctions

Early in ontogeny, Ig, TCR-alpha beta, and TCR-gamma delta lack N regions. In addition, Ig and TCR-gamma delta junctions preferentially occur at regions of short sequence homology, thus limiting junctional diversity for these neonatal lymphocyte populations. Here, we analyze the extent of heterogeneity in TCR-beta chain junctions made early in ontogeny. DNA and cDNA from fetal/neonatal thymocytes were amplified by polymerase chain reaction, and the V-D and D-J junctions from these randomly generated sequences were analyzed. The D-J junctions were very heterogeneous, and displayed little evidence of homology-directed recombination. The V beta 8-D and V beta 5-D junctions that we analyzed each had a particular junctional sequence that was created at the site of a two-nucleotide homology, but in each case that sequence only comprised 10 to 17% of the total sequences. This junctional heterogeneity of N region lacking TCR-beta chains can be partially explained by a relative paucity of homologies at the appropriate locations near the coding ends, particularly at the D-J junction, but other factors such as the sequence surrounding the homology may also contribute. Thus, TCR-beta chains have extensive junctional heterogeneity early in ontogeny before N regions begin to be added. Since TCR-alpha beta CDR3 plays a major role in binding antigenic peptides, this junctional heterogeneity is likely to be advantageous for establishing a diverse TCR repertoire. We suggest that the sequences of the coding ends of the TCR-alpha beta have been selected through evolution to avoid the restricted junctional diversity resulting from homology-directed recombination.     

Identification of HLA-A3-restricted cytotoxic T lymphocyte epitopes from carcinoembryonic antigen and HER-2/neu by primary in vitro immunization with peptide-pulsed dendritic cells

The human carcinoembryonic antigen (CEA) and HER-2/neu are potential target antigens for CTL specific immunotherapy for common malignancies such as breast, lung, colon, and gastric carcinomas. Several CTL epitopes restricted by HLA-A2, the most common human histocompatibility molecule, have been previously reported. However, to develop CTL-based immunotherapies for the general population, it is necessary to identify epitopes restricted by other common histocompatibility alleles. Here, we describe two HLA-A3-restricted CTL epitopes from the CEA and HER-2/neu antigens. HLA-A3 binding synthetic peptides from CEA and HER-2/neu were tested for immunogenicity by in vitro primary CTL induction protocol using peripheral blood mononuclear cells from normal healthy volunteers. One peptide from CEA (CEA[9(61)]: HLFGYSWYK) and one peptide from HER-2/neu (HER2[9(754)]: VLRENTSPK) were shown to induce CTL that was capable of killing a tumor cell line expressing HLA-A3 and the corresponding tumor-associated antigen. Additional MHC binding studies with the most common HLA molecules belonging to the HLA-A3 superfamily (HLA-A*1101, -A*3101, -A*3301, and -A*6801), demonstrated that CEA[9(61)] binds five of five A3 supertype molecules with high affinity, and the HER2[9(754)] epitope was able to bind to four of the same five alleles. These results indicate that these two new CTL epitopes should be immunogenic in individuals expressing either HLA-A3, or other members of the HLA-A3 superfamily.     

Spondyloarthropathies and HLA-B27 subtypes in the populations of the Russian North

The aim of the study was to investigate the role of HLA-B27 subtypes in development of ankylosing spondylitis and other seronegative spondylarthropathies. Using oligotyping techniques we studied native DNA of 219 HLA-B27 positive natives: 88 Chukotka residents and 131 Mordovians (Russian Ugro-Finnish population). Only subtypes HLA-B*2705 and B*2702 were revealed. A dominant subtype of HLA-B27 among the natives was HLA-B*2705: 99% among residents of Chukotka and 86% among Mordovians. It was established that among spondylarthropathic patients the frequency of B*2705 does not differ from its incidence in the studied populations. The data support the suggestion that several B27 subtypes and common genetic determinant of B27 gene may be involved in pathogenesis of spondylarthropathy.     

Yersinia-hsp60-reactive T cells are efficiently stimulated by peptides of 12 and 13 amino acid residues in a MHC class II (I-Ab)-restricted manner

Generation of the microbicidal oxidative burst in human neutrophils requires participation of four proteins, a membrane bound flavocytochrome beta-558, two soluble proteins termed p47-phox and p67-phox, and the Ras-related GTPase Rac. Because plant cells exposed to pathogens produce a similar oxidative burst, we have looked for similarities between the oxidase complexes of the two systems. Antibodies against human neutrophil p47-phox and p67-phox were used to immunoblot cell extracts from several plant cell lines and were found to cross-react with proteins of the same molecular weight. Furthermore, plant cell lines not previously shown to produce an oxidative burst, yet found to express these immunoreactive proteins, rapidly generated hydrogen peroxide in response to elicitation. Finally, diphenylene iodonium (DPI) and alpha-naphthol, known specific inhibitors of the NADPH oxidase in neutrophils, also inhibited the oxidative burst in soybean cell suspensions with similar Ki values (about 15 microM and 30 microM respectively). These results provide evidence for involvement of proteins related to the neutrophil oxidase complex in the defense-related oxidative burst of plants.     

Native peptide inhibition. Specific inhibition of type II phospholipases A2 by synthetic peptides derived from the primary sequence

The binding of low molecular weight type II phospholipase A2 (EC) to membrane surfaces and hydrolysis of phospholipid are thought to involve the formation of a hydrophobic channel into which a single substrate molecule diffuses before cleavage. The floor and right side of the channel are provided by hydrophobic residues 2, 5, and 9 of an amphipathic amino-terminal helix. The channel is postulated to form via a conformational change in this helix and inward movement of a hydrophobic flap (residue 69 side chain). We show that the amino-terminal tryptic peptide of human type II phospholipase A2 forms a noncovalent complex with the tryptic peptide from residues 70-74 of the enzyme. Further, the 70-74-peptide sequence (FLSYK) dose-dependently inhibits phospholipid hydrolysis in a mixed micelle assay. This native peptide inhibition also occurred with type II enzymes from Crotalus durissus and Crotalus atrox, which have different amino acid sequences at the amino terminus as well as different 70-74 regions of the molecules. Despite significant conservation of tertiary structure among the enzymes, inhibition by each peptide is specific to the enzyme from which the peptide sequence is derived. We propose that these native peptides inhibit enzyme activity via a sequence-specific, noncovalent interaction with the amino-terminal residues of the enzyme, thereby preventing the conformational change on binding to the micelle interface. These experiments demonstrate a new method for specific inhibition of phospholipase A2 which, in principle, would be applicable to other biologically active polypeptides and proteins.     

Extensive junctional diversity of Ig heavy chain rearrangements generated in the progeny of single fetal multipotent hematopoietic cells in the absence of selection

We analyzed the progeny of individual multipotent hemopoietic cells, derived from the para-aortic splanchopleura, the earliest identified source of lymphocyte precursors in pre-liver mouse embryos. Single precursors were expanded in an in vitro culture system that permits both commitment and differentiation of B cell precursors. We show that from one single multipotent progenitor we could obtain large numbers of B cell precursors that rearrange the Ig heavy chain genes and generate a repertoire as diverse as that observed in adult populations. N region additions are present at V(D)J junctions, showing that terminal deoxynucleotidyl transferase expression has been switched on and is not, consequently, an intrinsic property of adult stem cells. Throughout the culture period, cells show a majority of DJ vs V(D)J rearrangements and a ratio of 2:1 of nonproductive to productive V(D)J rearrangements, which is close to the expected frequency in the absence of selection. In addition, counterselection for D-J rearrangements in reading frame 2 is observed in V(D)J joints, and allelic exclusion was consistently observed. We conclude that of the three events associated with heavy chain rearrangement, two of them, namely allelic exclusion and counterselection of cells in which the D segment is in reading frame 2, are intrinsic to the cell, while selection of productive heavy chain rearrangements is induced in the bone marrow environment.     

Specificity in transcriptional regulation in the absence of specific DNA binding sites: the case of T7 lysozyme

Once osteoblasts have completed their bone-forming function, they are either entrapped in bone matrix and become osteocytes or remain on the surface as lining cells. Nonetheless, 50-70% of the osteoblasts initially present at the remodeling site cannot be accounted for after enumeration of lining cells and osteocytes. We hypothesized that the missing osteoblasts die by apoptosis and that growth factors and cytokines produced in the bone microenvironment influence this process. We report that murine osteoblastic MC3T3-E1 cells underwent apoptosis following removal of serum, or addition of tumor necrosis factor (TNF), as indicated by terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling and DNA fragmentation studies. Transforming growth factor-beta and interleukin-6 (IL-6)-type cytokines had antiapoptotic effects because they were able to counteract the effect of serum starvation or TNF. In addition, anti-Fas antibody stimulated apoptosis of human osteoblastic MG-63 cells and IL-6-type cytokines prevented these changes. The induction of apoptosis in MG-63 cells was associated with an increase in the ratio of the proapoptotic protein bax to the antiapoptotic protein bcl-2, and oncostatin M prevented this change. Examination of undecalcified sections of murine cancellous bone revealed the presence of apoptotic cells, identified as osteoblasts by their proximity to osteoid seams and their juxtaposition to cuboidal osteoblasts. Assuming an osteoblast life span of 300 h and a prevalence of apoptosis of 0.6%, we calculated that the fraction that undergo this process in vivo can indeed account for the missing osteoblasts. These findings establish that osteoblasts undergo apoptosis and strongly suggest that the process can be modulated by growth factors and cytokines produced in the bone microenvironment.     

Functional competence of T cells in the absence of glycosylphosphatidylinositol-anchored proteins caused by T cell-specific disruption of the Pig-a gene

T lymphocytes express various glycosylphosphatidylinositol (GPI)-anchored surface proteins, such as Thy-1 and Ly-6A. However, functional contribution of GPI-anchored proteins in T cell activation is as yet poorly understood. Here we report the generation of mutant mice deficient in the expression of GPI-anchored molecules exclusively in their T cells. We established mice carrying three identically oriented lox-P sites within the Pig-a gene, which encodes a component essential for the initial step of GPI anchor biosynthesis. These mice were crossed with mice carrying the Cre recombinase gene driven by the T cell-specific p56lck proximal promoter. Offspring carrying both the lox-P-containing Pig-a gene and the Cre transgene exhibited almost complete loss of the surface expression of GPI-anchored molecules on peripheral T cells. Interestingly, those T cells deficient in GPI-anchored molecules were capable of responding to T cell receptor stimulation in vitro and in vivo. These results indicate that T cells lacking the expression of GPI-anchored molecules are functionally competent in exerting TCR-mediated immune responses.     

Comparison of primary sensitization of naive human T cells to varicella-zoster virus peptides by dendritic cells in vitro with responses elicited in vivo by varicella vaccination

Dendritic cells (DC) are potent APC during primary and secondary immune responses. The first objective of this study was to determine whether human DC mediate in vitro sensitization of naive CD4+ T cells to epitopes of the immediate early 62 (IE62) protein of varicella zoster virus (VZV). The induction of CD4+ T cell proliferative responses to eight synthetic peptides representing amino acid sequences of the VZV IE62 protein was assessed using T cells and DC from VZV-susceptible donors. The second objective was to compare in vitro responses of naive T cells with responses to VZV peptides induced in vivo after immunization with varicella vaccine. T cell proliferation was induced by three peptides, P1, P4, and P7, in 71-100% of the donors tested before and after vaccination using DC as APC. Monocytes were effective APC for VZV peptides only after immunization. Two peptides, P2 and P8, induced naive T cell proliferation less effectively and were also less immunogenic for T cells from vaccinated or naturally immune donors. T cell recognition of specific peptides was concordant between naive, DC-mediated responses, and postvaccine responses using monocytes as APC in 69% of comparisons (p = 0.05; chi2); the predictive value of a positive response to an IE62 peptide before immunization for T cell sensitization in vivo was 82%. These observations indicate that primary T cell responses detected in vitro using DC as APC may be useful to characterize the potential immunogenicity of viral protein epitopes in vivo.     

IL-12 enhances antibody responses to T-independent polysaccharide vaccines in the absence of T and NK cells

Polysaccharide vaccines to encapsulated bacteria such as Neisseria meningitidis and Streptococcus pneumoniae are weakly immunogenic due to their T-independent (TI) nature. Even when converted to T-dependent forms through conjugation to foreign proteins, polysaccharides induce responses that are deficient in many respects, such as induction of murine IgG2a Ab, the isotype that mediates optimal complement fixation and opsonization. We now show that IL-12 treatment of mice induces significantly increased levels of IgG2a Ab to the model TI-2 Ag, DNP-Ficoll, and to vaccines composed of polysaccharides from pneumococci and meningococci. Use of immunodeficient mice lacking T cells and/or NK cells demonstrated that such cells were not responsible for the observed Ab enhancement. Furthermore, the use of IFN-gamma knockout mice showed that stimulation of TI-2 Ab responses by IL-12 was only partially dependent on IFN-gamma. The ability of IL-12 to dramatically enhance TI Ab responses suggests that IL-12 will be useful as a powerful vaccine adjuvant to induce protective immune responses against encapsulated pathogens.     

Binding of peptides naturally presented by HLA-B27 to the differentially disease-associated B*2704 and B*2706 subtypes, and to mutants mimicking their polymorphism

B*2704 and B*2706 are closely related HLA-B27 subtypes of which the former but not the latter is associated to ankylosing spondylitis. Their peptide specificity relative to other disease-associated subtypes was analyzed by testing binding of self-peptides naturally presented by B*2705 or B*2702, and synthetic analogs, to B*2704, B*2706, and site-specific mutants mimicking their changes. Peptides with basic, aliphatic or aromatic C-terminal residues bound to B*2705 with similar affinity. In B*2704 C-terminal aliphatic/ aromatic residues were preferred. B*2706 discriminated drastically between polar and nonpolar C-terminal residues, showing strong preference for Leu and Phe, and less than B*2704 for basic and Tyr residues. Loss of single acidic charges (D > S77, D > Y116) increased preference for C-terminal Leu and Phe, but allowed efficient binding of peptides with basic residues or Tyr. Their gain (V > E152, H > D114) maintained wide C-terminal specificity, but severely impaired binding, presumably by disrupting interactions with internal peptide residues. This was compensated by Y116 in the double D114Y116 mutant. The specificity of B*2704 and B*2706 was explained only partially by the separate effects of single mutations, indicating that novel properties arise from concomitant changes at various positions. For instance, specificity of B*2706 for nonpolar C-terminal residues required simultaneous removal of Asp77 and Asp116. B*2706 differed from B*2705, B*2702, and B*2704 in its lower suitability for C-terminal Tyr, suggesting that this feature might be relevant for HLA-B27 association to spondyloarthropathy.     

Artificial mutations and natural variations in the CD46 molecules from human and monkey cells define regions important for measles virus binding

CD46 was previously shown to be a primate-specific receptor for the Edmonston strain of measles virus. This receptor consists of four short consensus regions (SCR1 to SCR4) which normally function in complement regulation. Measles virus has recently been shown to interact with SCR1 and SCR2. In this study, receptors on different types of monkey erythrocytes were employed as "natural mutant proteins" to further define the virus binding regions of CD46. Erythrocytes from African green monkeys and rhesus macaques hemagglutinate in the presence of measles virus, while baboon erythrocytes were the least efficient of the Old World monkey cells used in these assays. Subsequent studies demonstrated that the SCR2 domain of baboon CD46 contained an Arg-to-Gln mutation at amino acid position 103 which accounted for reduced hemagglutination activity. Surprisingly, none of the New World monkey erythrocytes hemagglutinated in the presence of virus. Sequencing of cDNAs derived from the lymphocytes of these New World monkeys and analysis of their erythrocytes with SCR1-specific polyclonal antibodies indicated that the SCR1 domain was deleted in these cells. Additional experiments, which used 35 different site-specific mutations inserted into CD46, were performed to complement the preceding studies. The effects of these artificial mutations were documented with a convenient binding assay using insect cells expressing the measles virus hemagglutinin. Mutations which mimicked the change found in baboon CD46 or another which deleted the SCR2 glycosylation site reduced binding substantially. Another mutation which altered GluArg to AlaAla at positions 58 and 59, totally abolished binding. Finally, the epitopes for two monoclonal antibodies which inhibit measles virus attachment were mapped to the same regions implicated by mutagenesis.     

Chimeric receptors providing both primary and costimulatory signaling in T cells from a single gene product

Single chain Fv chimeric receptors, or T-bodies, are described with intracellular sequences comprising the costimulatory signaling domain of CD28 in series with the zeta-chain from the TCR complex. Using an engineered human single chain Fv derived from P67, an mAb with specificity for human CD33, and a spacer comprising an Ab hinge region with either Fcgamma or part of the CD28 extracellular region, fusion molecules were constructed to test the ability of single chain designs to mediate both primary signaling and costimulation from one extracellular binding event. Constructs with the CD28 signaling domain proximal and the zeta-chain distal to the membrane were found to express more efficiently in Jurkat than constructs with the opposite orientation and were capable of mediating up to 20 times more IL-2 production on stimulation with solid phase Ag when compared with transfectants expressing chimeric receptors with zeta-chain intracellular signaling domains only. IL-2 production was specific to Ag challenge and was completely inhibited by incubation with free Ab of the same specificity as the extracellular binding site of the construct, but not by an isotype-matched control Ab. The CD28 intracellular domain of these fusion proteins was shown to be capable of binding the p85 subunit of phosphatidylinositol 3'-kinase. These constructs represent the first of a new generation of single gene multidomain chimeric receptors capable of mediating both primary and costimulatory signaling specifically from a single extracellular recognition event.     

Homology of partial primary sequences between alpha-enolase and a suppressive lymphokine from human T cells

Cytosolic and mitochondrial alterations induced by exposure of rat astroglial primary cultures to reactive oxygen species (ROS) generated by a xanthine/xanthine oxidase (X/XO) mixture or by lipopolysaccharide (LPS) have been investigated biochemically and immunochemically. In the presence of ROS generated by X/XO, a significant decrease in Cu,Zn superoxide dismutase (Cu,Zn-SOD) and in glutamine synthetase (GS) activity was observed whereas mitochondrial Mn-SOD activity and enzyme protein levels were significantly enhanced. Similar effects on GS, Cu,Zn- and Mn-SOD activities were observed by glucose/glucose oxidase treatment of the cells. Addition of LPS to the cell growth medium also specifically induces Mn-SOD synthesis but was without effect on Cu,Zn-SOD. It is suggested that in all these tested situations, hydrogen peroxide could represent a specific inducer of the observed phenomenon and it may therefore be considered as an intracellular messenger involved in the regulation of some aspects of astroglial oxidative metabolism, particularly the defence against ROS.     

Characteristics of endogenous peptides eluted from the class I MHC molecule HLA-B7 determined by mass spectrometry and computer modeling

Microcapillary HPLC electrospray ionization tandem mass spectrometry was used to sequence 15 peptides eluted from HLA-B7. Sequence alignment implicated four peptide positions in specific interactions with the class I molecule, and their importance was confirmed using synthetic peptides. Because no crystal structure for HLA-B7 was available, computer-assisted modeling was used to understand novel aspects of peptide binding specificity and to accurately predict the effect of defined changes in peptide structure. The results demonstrate that mass-spectrometric sequencing coupled with computer-assisted modeling can be used in the absence of a crystal structure to make accurate predictions concerning requirements for peptide binding to class I molecules. These techniques may be valuable to predict or engineer T cell epitopes.     

Isolation, sequence, and bioactivity of FMRFamide-related peptides from the locust ventral nerve cord

The electrochemical behaviour of the bioreductive redox active nitroimidazole drug metronidazole has been examined in the presence and absence of the DNA bases using three electrochemical techniques, all of which indicate the capacity for interaction between reduced products and DNA bases. The 4-electron metronidazole (RNO2) metronidazole-hydroxylamine (RNHOH) couple in an aqueous medium shows a positive shift in reduction potential upon addition of thymine, adenine and guanine, but a negative shift for cytosine. Interpretation of these results for an irreversible process is, however, inconclusive. In dimethylformamide/H2O the presence of DNA base on the one-electron addition product, the nitro radical anion, was examined by cyclic voltammetry. All except guanine resulted in interaction with the metronidazole nitro radical anion (RNO2-), as measured by the decrease in the return-to-forward peak current ratio, in the following order of increasing reactivity: cytosine, adenine and thymine (at a metronidazole: base ratio of 1:1). The increase in the stability of the radical anion by increasing the pH of the dimethylformamide/H2O medium resulted in a decreased reaction with thymine.