Structural and functional studies of trans-encoded HLA-DQ2.3 (DQA1*03:01/DQB1*02:01) protein molecule

MHC class II molecules are composed of one α-chain and one β-chain whose membrane distal interface forms the peptide binding groove. Most of the existing knowledge on MHC class II molecules comes from the cis-encoded variants where the α- and β-chain are encoded on the same chromosome. However, trans-encoded class II MHC molecules, where the α- and β-chain are encoded on opposite chromosomes, can also be expressed. We have studied the trans-encoded class II HLA molecule DQ2.3 (DQA1*03:01/DQB1*02:01) that has received particular attention as it may explain the increased risk of certain individuals to type 1 diabetes. We report the x-ray crystal structure of this HLA molecule complexed with a gluten epitope at 3.05 Å resolution. The gluten epitope, which is the only known HLA-DQ2.3-restricted epitope, is preferentially recognized in the context of the DQ2.3 molecule by T-cell clones of a DQ8/DQ2.5 heterozygous celiac disease patient. This preferential recognition can be explained by improved HLA binding as the epitope combines the peptide-binding motif of DQ2.5 (negative charge at P4) and DQ8 (negative charge at P1). The analysis of the structure of DQ2.3 together with all other available DQ crystal structures and sequences led us to categorize DQA1 and DQB1 genes into two groups where any α-chain and β-chain belonging to the same group are expected to form a stable heterodimer.

Assessing possible celiac disease by an HLA-DQ2-gliadin Tetramer Test

OBJECTIVES

Investigation of uncertain celiac disease (CD) in patients already on a gluten-free diet (GFD) is difficult. We evaluated HLA-DQ2-gliadin tetramers for detection of gluten-specific T cells in peripheral blood and histological changes in the duodenum after a short gluten challenge as a diagnostic tool.

METHODS

HLA-DQ2+ individuals on a GFD for at least 4 weeks were investigated; 35 with uncertain diagnosis, 13 CD patients, and 2 disease controls. All participants had a challenge with four slices of gluten-containing white bread, daily for 3 days (d1-d3). An esophagogastroduodenoscopy with biopsy sampling was done on d0 and d4. Biopsies were scored according to revised Marsh criteria. Peripheral blood CD4+ T cells were isolated, stained with HLA-DQ2-gliadin peptide tetramers, and analyzed by flow cytometry on d0 and d6.

RESULTS

After challenge, a positive tetramer test was seen in 11/13 CD patients. Four of these subjects also showed typical histological changes on challenge. Of the 35 patients with uncertain diagnosis, 3 were diagnosed with CD. Two of these three patients had both positive tetramer staining and histological changes in biopsies after challenge.

CONCLUSIONS

Tetramer staining for gluten-specific T cells is a sensitive method in detecting an immune response in CD patients after a short gluten challenge. The prevalence of CD in the group with self-prescribed GFD was about 10%.

Construction, evaluation and refinement of a large human antibody phage library based on the IgD and IgM variable gene repertoire

The ability to isolate antibodies against any antigen of interest has become increasingly important as antibodies have proved their utility both in antigen detection, quantification and as specific in vivo targeting agents. To this end, we have constructed a large antibody phage library in the single chain Fv (scFv) phagemid format based on the naive human variable (V) gene repertoire dictated by IgD and IgM. Optimizing each step of the library construction has resulted in a highly diverse and functional library, as assessed by sequencing analysis, large-scale automated expression analysis and antigen screening. Furthermore, the versatile format of the library, which comprises 14 separate sub-libraries, adds considerably flexibility with respect to which part of the antibody repertoire that is to be probed. This versatility has been further exploited to generate a refined antibody library, which exhibits one of the highest prokaryotic expression levels reported to date for a naive repertoire. The construction of the refined library was based on the functional purification of expressed V genes in the context of the protein L interaction with correctly folded V genes of the kappa light chain family. Antigen screening of this library indicated that the functional purification improved the ability to retrieve antigen specific antibodies, but at the cost of potential loss of diversity in the isolated repertoire.

Covalent antibody display--an in vitro antibody-DNA library selection system

The endonuclease P2A initiates the DNA replication of the bacteriophage P2 by making a covalent bond with its own phosphate backbone. This enzyme has now been exploited as a new in vitro display tool for antibody fragments. We have constructed genetic fusions of P2A with single-chain antibodies (scFvs). Linear DNA of these fusion proteins were processed in an in vitro coupled transcription–translation mixture of Escherichia coli S30 lysate. Complexes of scFv–P2A fusion proteins covalently bound to their own DNA were isolated after panning on immobilized antigen, and the enriched DNAs were recovered by PCR and prepared for the subsequent cycles of panning. We have demonstrated the enrichment of scFvs from spiked libraries and the specific selection of different anti-tetanus toxoid scFvs from a V-gene library with 50 million different members prepared from human lymphocytes. This covalent antibody display technology offers a complete in vitro selection system based exclusively on DNA–protein complexes.

Direct isolation of recombinant human antibodies against group B Neisseria meningitidis from scFv expression libraries

The successful generation of human antibodies from large nai;ve antibody libraries requires iterative selection steps. Here, we describe a new and fast method for the isolation of high affinity antibodies directly from human single chain Fv antibody (scFv) expression libraries. Escherichia coli scFv expression libraries were made from peripheral blood lymphocytes from four individuals vaccinated with group B Neisseria meningitidis outer membrane vesicle (OMV) vaccine. Forty thousand clones were directly screened for antibodies binding N. meningitidis strain 44/76 (B:15:P1.7,16). Of 430 specific clones detected, 225 candidates were isolated and re-screened against the N. meningitidis strains NZ-98/254 (B:4:P1.7b,4) giving 4% cross-reactive clones. Antibodies were further characterized by DNA sequencing, ELISA and surface plasmon resonance (SPR) analysis, showing broad V-gene diversity and nanomolar scFv affinities. Antibodies derived by this method may assist in the discovery and development of new vaccine antigens as well as therapeutic antibody agents for the treatment of meningococcal diseases.

Identification of scFv antibody fragments that specifically recognise the heroin metabolite 6-monoacetylmorphine but not morphine

Use of phage display of recombinant antibodies and large repertoire naïve antibody libraries for identifying antibodies of high specificity has been extensively reported. Nevertheless, there have been few reported antibodies to haptens that have originated from naïve antibody libraries with potential use in diagnostics. We have used chain shuffling of lead single-chain fragment variable (scFv) antibodies, isolated from a naïve antibody library, to screen for antibodies that specifically recognise the major metabolite of heroin, 6-monoacetylmorphine (6MAM). The antibodies were identified by screening high-density colonies of Escherichia coli expressing soluble scFv antibody fragments without prior expression on bacteriophage (phage display). The antibodies recognise 6MAM with affinities of 1-3x10(-7) M with no crossreactivity to morphine. These antibodies can potentially be used for developing a rapid immunoassay in drug-testing programs. To our knowledge, this is the first report of an antibody that distinguishes 6MAM from its de-acetylated form, morphine.

The safety and efficacy of MenoTreat, a new balloon device for thermal endometrial ablation

BACKGROUND

An evaluation of the performance and safety of the prototype of a new device, MemoTreat (Atos Medical) for thermal endometrial balloon ablation in patients with menorrhagia. The evaluation was performed at four Swedish hospitals.

METHODS

In total 51 consecutive, premenopausal patients, suffering from menorrhagia due to benign causes and not responding to conventional treatment, were treated between March 1997 and March 1998. The treatment entailed heated (85 degrees C) sterile saline circulated in a uterine balloon at a treatment pressure of 200 mmHg for 11 minutes. The procedure was performed mainly under general anesthesia and no pre-treatment endometrial thinning was performed. A validated pictorial assessment technique was used to evaluate changes in menstrual blood loss before and after treatment. Changes in quality of life and severity of dysmenorrhea were also evaluated. Data analysis was based on the 'intention to treat' method.

RESULTS

The success rate in terms of a 50% reduction in menstrual bleeding was 84.3% at 6 months after treatment. Five patients became amenorrheic. The quality of life assessment showed substantial improvement and the severity of dysmenorrhea was markedly reduced. No intra-operative treatment complications occurred and the post-treatment morbidity was similar to that reported for other similar treatment methods.

CONCLUSIONS

MenoTreat significantly reduced menstrual bleeding in menorrhagic patients, with a concomitant improvement in quality of life. The findings in this study resulted in a redesigned device with a thinner balloon catheter, improved cervical protection and treatment temperatures kept at a constant level.

Immunolocalization of electroneutral Na-HCO(3)(-) cotransporter in rat kidney

An electroneutral Na-HCO(3)(-) cotransporter (NBC(N)1) was recently cloned, and Northern blot analyses indicated its expression in rat kidney. In this study, we determined the cellular and subcellular localization of NBC(N)1 in the rat kidney at the light and electron microscopic level. A peptide-derived antibody was raised against the COOH-terminal amino acids of NBC(N)1. The affinity-purified antibody specifically recognized one band, approximately 180 kDa, in rat kidney membranes. Peptide-N-glycosidase F deglycosylation reduced the band to approximately 140 kDa. Immunoblotting of membrane fractions from different kidney regions demonstrated strong signals in the inner stripe of the outer medulla (ISOM), weaker signals in the outer stripe of the outer medulla and inner medulla, and no labeling in cortex. Immunocytochemistry demonstrated that NBC(N)1 immunolabeling was exclusively observed in the basolateral domains of thick ascending limb (TAL) cells in the outer medulla (strongest in ISOM) but not in the cortex. In addition, collecting duct intercalated cells in the ISOM and in the inner medulla also exhibited NBC(N)1 immunolabeling. Immunoelectron microscopy demonstrated that NBC(N)1 labeling was confined to the basolateral plasma membranes of TAL and collecting duct type A intercalated cells. Immunolabeling controls were negative. By using 2, 7-bis-carboxyethyl-5,6-caboxyfluorescein, intracellular pH transients were measured in kidney slices from ISOM and from mid-inner medulla. The results revealed DIDS-sensitive, Na- and HCO(3)(-)-dependent net acid extrusion only in the ISOM but not in mid-inner medulla, which is consistent with the immunolocalization of NBC(N)1. The localization of NBC(N)1 in medullary TAL cells and medullary collecting duct intercalated cells suggests that NBC(N)1 may be important for electroneutral basolateral HCO(3)(-) transport in these cells.

Three-colour flow cytometric immunophenotyping in HIV-patients; comparison to dual-colour protocols

Flow cytometric measurement of circulating CD4+ lymphocytes is important in the evaluation of disease progression in HIV-infected patients. Development of dyes that can be exited at 488 nm and have emission maximum in the far red area has made three-colour protocols, together with fluorescein isothiocyanate (FITC) and R-phycoerythrin (PE), possible in most clinical flow cytometers. We report here the comparison of a two-tube, three-colour protocol (including CD45/CD4/ CD3 and CD8/CD4/CD3) with our conventional dual-colour protocol. No significant differences were found between percentage of CD3+ lymphocytic cells determined with three different antibody combinations. When the CD8/CD4/CD3 combination was used a systematic overestimation of CD3+ CD4+% cells was found. This turned out to be caused by the formation of 'CD8-escapees'. These are clumps of CD8+ cells that fall outside the lymphocyte gating region, principally because of high side scatter. The problem can be overcome by rigorous vortexing to loosen aggregates. The lymphocyte gating principle used in this protocol (gating on a side scatter/CD45 dot plot) is readily applicable to other antibody combinations. This was demonstrated by measuring CD5+ B lymphocytes, a subset receiving increasing attention in the study of HIV-induced immune deviations. We conclude that our three-colour protocol for CD4+ T-lymphocyte determinations offers significant advantages to the conventional dual-colour method, and we suggest that when possible anti-CD45 be added to dual-colour combinations in order to improve lymphocyte gating.

Total hip replacement in patients aged 80 years and older

Total hip replacement was performed in 27 patients aged 80 years and older. In the early postoperative period, medical complications occurred in 13 patients and arthroplasty-related complications in 5 patients. At the time of the follow-up, after an average of 31 months, there was one case of acetabular cup loosening, which was revised. Twenty of 22 patients were free from pain at rest, and the social function of the patients had remained almost unchanged.

Safety of Shelf-Stable Canned Cured Meats

Shelf-stable canned cured meats (SSCCM) are preserved by thermodestruction of the vegetative microflora, partial destruction of the microbial spores, and subsequent inhibition of the surviving spores. Inhibition depends primarily on the concentration of salt, nitrite input and the severity of the thermoprocess. On the basis of published experimental work, the botulism risk of SSCCM may be estimated, either as the equivalent of the decimal heat destruction of spores, taking into account the combined destruction and inhibition in SSCCM (log 1/P), or as the decimal number of cans needed for a single can to become toxic, i.e., log 1/(P × i), where P is the probability of individual spores developing and producing toxin in the processed can, and i is the incidence of Clostridium botulinum spores in the raw product. The experimental data demonstrate that the 12 D concept (or its equivalent) is not applicable to SSCCM and cast doubt on the adequacy of the F₀ value as a measure of the effective heat treatment for this type of product. Research data on the safety of SSCCM are limited and do not allow us at present to propose minimal requirements of the essential safety factors. Instead, our risk assessment relies heavily on commercial practice and experience. In analogy to log 1/(P × i), the safety of commercial cans is expressed as the decimal number of cans produced per can causing severe illness, arbitrarily designated SU (safety units). Estimated SU values for defined commercial luncheon meats, canned cured ham and sausages, range from > 7 to > 9. Provided that the microbial spore levels of both the raw meat and non-meat ingredients of SSCCM are rigidly controlled, the SU estimates allow us to specify minimum safety requirements for the major groups of shelf-stable canned cured meats.