Recombinantly Expressed Tagged SUrface Protein (RETSUP) assay: a new diagnostic system for the detection of antibodies to platelets

BACKGROUND

Current assays for the detection of (allo)antibodies to platelet antigens are often laborious and widely based on the presence of well-characterized donor platelets.

OBJECTIVES

To develop an easy-to-perform, sensitive, and specific test for the detection of antibodies against platelet antigens, in particular, glycoprotein (GP) antigens, called "Recombinantly Expressed Tagged SUrface Protein" (RETSUP) assay, which does not require donor platelets.

METHODS

Twin-Strep-tagged GP complexes were recombinantly expressed in human embryonic kidney 293 cells after stable transfection. These cell lines were used as antigen sources in the RETSUP assay, combining cell-based and enzyme-linked immunosorbent assay-based assay procedures. The assay performance was tested with recombinant antibodies, anti-human platelet antigen (HPA) reference plasmas, and anti-HPA patient sera.

RESULTS

Human embryonic kidney 293 cell lines stably expressing either Twin-Strep-labeled GPIa/IIa, GPIIb/IIIa, GPIb/IX, or GPIb/IX/V complexes or GPV as well as the distinct HPA-1, HPA-3, and HPA-5 epitopes were successfully generated. Applying the generated GP-expressing cell lines, the developed RETSUP assay proved very sensitive and specific with recombinant antibodies targeting different GPs and human plasma/serum samples. The results of the test were not affected by the GP carrying the Twin-Strep-tag or by using freshly harvested or cryopreserved cells.

CONCLUSION

The RETSUP assay is an easy-to-perform, sensitive, and specific assay for the detection of plasma/serum antibodies to platelet GP, with performance comparable to or better than those of current state-of-the-art assays in antiplatelet antibody diagnostics. Owing to the recombinant nature of the target antigens, it can be easily adapted to detect antibodies in other antibody-mediated diseases.

A Glanzmann thrombasthenia family associated with a TUBB1-related macrothrombocytopenia

BACKGROUND

Macrothrombocytopenia (MTP) is a rare but enigmatic complication of Glanzmann thrombasthenia (GT), an inherited bleeding disorder caused by the absence of platelet aggregation due to deficiencies of the αIIbβ3 integrin.

OBJECTIVES

We report a family with type I GT and a prolonged bleeding time but unusually associated with congenital mild thrombocytopenia and platelet size heterogeneity with giant forms.

METHODS AND RESULTS

Sanger sequencing of DNA from the propositus identified 2 heterozygous ITGB3 gene mutations: p.P189S and p.C210S both of which prevent αIIbβ3 expression and are causative of GT but without explaining the presence of enlarged platelets. High-throughput screening led to the detection of a predicted disease-causing heterozygous mutation in the TUBB1 gene: p.G146R, encoding β1-tubulin, a component of the platelet cytoskeleton and a gene where mutations are a known cause of MTP.

CONCLUSIONS

Family screening confirmed that this rare phenotype results from oligogenic inheritance while suggesting that the GT phenotype dominates clinically.

N-glycosylation and topology of the human SLC26 family of anion transport membrane proteins

The human solute carrier (SLC26) family of anion transporters consists of 10 members (SLCA1-11, SLCA10 being a pseudogene) that encode membrane proteins containing ~12 transmembrane (TM) segments with putative N-glycosylation sites (-NXS/T-) in extracellular loops and a COOH-terminal cytosolic STAS domain. All 10 members of the human SLC26 family, FLAG-tagged at the NH2 terminus, were transiently expressed in HEK-293 cells. While most proteins were observed to contain both high-mannose and complex oligosaccharides, SLC26A2 was mainly in the complex form, SLC26A4 in the high-mannose form, and SLC26A8 was not N-glycosylated. Mutation of the putative N-glycosylation sites showed that most members contain multiple N-glycosylation sites in the second extracytosolic (EC) loop, except SLC26A11, which was N-glycosylated in EC loop 4. Immunofluorescence staining of permeabilized cells localized the proteins to the plasma membrane and the endoplasmic reticulum, with SLC26A2 highly localized to the plasma membrane. N-glycosylation was not a necessary requirement for cell surface expression as the localization of nonglycosylated proteins was similar to their wild-type counterparts, although a lower level of cell-surface biotinylation was observed. No immunostaining of intact cells was observed for any SLC26 members, demonstrating that the NH2-terminal FLAG tag was located in the cytosol. Topological models of the SLC26 proteins that contain an even number of transmembrane segments with both the NH2 and COOH termini located in the cytosol and utilized N-glycosylation sites defining the positions of two EC loops are presented.

Identification of a new HLA-A2-restricted T-cell epitope within HM1.24 as immunotherapy target for multiple myeloma

OBJECTIVE

The aim of this study was identification of human leukocyte antigen (HLA)-A2-restricted T-cell epitopes within the HM1.24 antigen as target for multiple myeloma (MM)-directed specific peptide-based immunotherapy.

METHODS

The HM1.24 sequence was scanned for immunogenic peptides using the HLA-binding prediction software SYFPEITHI and BIMAS. Peripheral blood mononuclear cells from HLA-A2(+) healthy volunteers/blood donors (ND) were stimulated with autologous HM1.24-peptide-loaded dendritic cells, and expanded in vitro. Activation of T cells was assessed by ELISpot and cytotoxicity by (51)Chromium ((51)Cr)-release assays. T2-cells pulsed with irrelevant peptide, the HM1.24(-)/HLA-A2(+) breast carcinoma cell line MCF-7 and the HM1.24(+)/HLA-A2(-) myeloma cell line RPMI-8226 were used as controls. Expression of the HM1.24 gene (BST2) was assessed using purified plasma cells and Affymetrix-U133A+B microarrays. Frequency of peptide-specific CD8(+) T cells was detected using the flow-cytometric tetramer technique.

RESULTS

Of eight nona-peptides with the highest probability of binding to HLA-A2, the HM1.24 aa22-30 peptide (LLLGIGILV) showed the most frequent activation of CD8(+) T cells in healthy volunteers (specific activation in 8 of 11 [73%] ND; compared with 5-19% for the 7 other HM1.24 peptides). Antigen recognition by the HM1.24 aa22-30-specific CD8(+) T cells was HLA-A2-restricted (ELISpot with HLA-A2-blocking antibodies: median, 15; range, 14-18 spots/well; isotype-control antibodies: median, 47; range, 44-48). HM1.24-aa22-30-specific CD8(+) T cells lysed HLA-A2(+) myeloma-derived cell lines ((51)Cr-release assay: XG-1 vs MCF-7, 91% vs 0%; U266 vs MCF-7, 38% vs 4.2%; IM-9 vs RPMI-8226, 22% vs 0%). Using the cross-reactive Neisseria meningitidis peptide LLSLGIGILV-specific CD8(+) T cells recognizing target cells loaded with the HM1.24 aa22-30 peptide (LLLGIGILV) as well as the myeloma-derived cell line U266 could be expanded from MM patients. The HM1.24 gene was expressed at comparable levels by plasma cells from 65 MM patients, 7 patients with monoclonal gammopathy of undetermined significance, and 7 ND.

CONCLUSIONS

HM1.24 aa22-30 is a newly identified HLA-A2-restricted T-cell epitope that is processed and presented by major histocompatibility complex class I. Specifically activated CD8(+) T cells are able to lyse MM cell lines. We conclude that HM1.24 aa22-30 represents a suitable candidate target for a specific peptide-based immunotherapy of MM.

Soluble form of the triggering receptor expressed on myeloid cells-1 as a marker of microbial infection

Sepsis is a common cause of morbidity and mortality in intensive care units. Unfortunately, there is no gold standard for diagnosing sepsis as clinical and laboratory signs are neither sensitive enough nor specific enough, and microbiological studies often remain negative. Thus, there is a need for clinical or laboratory tools to distinguish between sepsis and non-infectious inflammatory disorders. Among the potentially useful markers of sepsis, procalcitonin has been suggested to be the most promising, although results are variable depending on the severity of illness and degree of infection in the patient population studied. The triggering receptor expressed on myeloid cells-1 (TREM-1) is a member of the immunoglobulin superfamily, of which expression is upregulated on phagocytic cells in the presence of bacteria or fungi. Here we report on the potential usefulness of assessing the soluble form of TREM-1 (sTREM-1) in biological fluids for the diagnosis of microbial infection.

A major role for Mcl-1 antiapoptotic protein in the IL-6-induced survival of human myeloma cells

Interleukin-6 (IL-6) is a major survival factor for malignant plasma cells involved in multiple myeloma. Using an RNase protection assay, we looked for gene expression of 10 anti- and proapoptotic Bcl-2-family proteins in 12 IL-6-dependent human myeloma cell lines (HMCL). A high Mcl-1 gene expression was found in all HMCLs and the other genes were variably expressed. Out of the 10 Bcl-2-family members, only the Mcl-1 gene was regulated by IL-6. Upon starvation of IL-6, Mcl-1 gene expression decreased in association with myeloma cell apoptosis and was upregulated after adding IL-6 again in association with myeloma cell survival. A constitutive Mcl-1 expression was induced with an Mcl-1-GFP retrovirus in two IL-6-dependent HMCLs. The Mcl-1 HMCLs have a marked reduced apoptosis upon IL-6 starvation compared to HMCLs transduced with control GFP retrovirus and may grow without adding IL-6. These data emphasize the major role of Mcl-1 antiapoptotic protein in the IL-6-induced survival of human myeloma cells.

Serotonin transporter gene polymorphisms and hyperserotonemia in autistic disorder

Previous studies have provided conflicting evidence regarding the association of the serotonin transporter (5-HTT) gene with autism. Two polymorphisms have been identified in the human 5-HTT gene, a VNTR in intron 2 and a functional deletion/insertion in the promoter region (5-HTTLPR) with short and long variants. Positive associations of the 5-HTTLPR polymorphism with autism have been reported by two family-based studies, but one found preferential transmission of the short allele and the other of the long allele. Two subsequent studies failed to find evidence of transmission disequilibrium at the 5-HTTLPR locus. These conflicting results could be due to heterogeneity of clinical samples with regard to serotonin (5-HT) blood levels, which have been found to be elevated in some autistic subjects. Thus, we examined the association of the 5-HTTLPR and VNTR polymorphisms of the 5-HTT gene with autism, and we investigated the relationship between 5-HTT variants and whole-blood 5-HT. The transmission/disequilibrium test (TDT) revealed no linkage disequilibrium at either loci in a sample of 96 families comprising 43 trios and 53 sib pairs. Furthermore, no significant relationship between 5-HT blood levels and 5-HTT gene polymorphisms was found. Our results suggest that the 5-HTT gene is unlikely to play a major role as a susceptibility factor in autism.

Hypolocomotor effects of acute and daily d-amphetamine in mice lacking the dopamine transporter

RATIONALE

Mice lacking the dopamine transporter (DAT(-/-)) exhibit high extracellular dopamine levels and marked hyperactivity. This hyperlocomotion is paradoxically decreased by acute administration of amphetamine-like psychostimulants, an effect that has been previously related to the activation of serotonergic neurotransmission.

OBJECTIVES

The goal of the present study was to investigate the effects of acute and daily administration of d-amphetamine on the locomotor activity of DAT(-/-) mice and examine the development of behavioral sensitization. In addition, we tested the implication of the serotonin system in the observed effects.

METHODS

DAT(+/+), DAT(+/-), and DAT(-/-) mice were injected with acute amphetamine (0, 0.3, 1, 3, or 10 mg/kg, SC), repeated amphetamine (1 mg/kg for 8 days, SC), or with the serotonin reuptake inhibitor fluoxetine (0, 5, 10, or 20 mg/kg, SC) and their locomotor activity was evaluated. Moreover, the expression of the serotonin transporter and 5-HT(1A) receptors in the brain of DAT(-/-) mice was studied using autoradiography.

RESULTS

Acute and repeated d-amphetamine injection (1 mg/kg) induced an hypolocomotor response in DAT(-/-) and DAT(+/-) mice, but only DAT(+/-) mice developed locomotor sensitization to the drug. Acute treatment with fluoxetine decreased locomotion in DAT(-/-) mice in a dose-dependent manner. The common hypolocomotor effect induced by d-amphetamine and fluoxetine in DAT(-/-) mice suggests an action on the serotonin transporter. However, autoradiography of the serotonin transporter and 5-HT(1A) receptors showed normal density and distribution in the brain, suggesting no compensatory effects due to the deletion of the DAT.

CONCLUSIONS

These findings indicate that partial or total DAT gene deletion result in decreased locomotion in response to d-amphetamine and modify behavioral sensitization depending on the proportion of DAT removed, suggesting that inhibition of the DAT is necessary for the development of sensitization to psychostimulant drugs.

Non-invasive investigation of inflammatory bowel disease

The assessment of inflammatory activity in intestinal disease in man can be done using a variety of different techniques. These range from the use of non-invasive acute phase inflammatory markers measured in plasma such as C reactive protein (CRP) and the erythrocyte sedimentation rate (ESR) (both of which give an indirect assessment of disease activity) to the direct assessment of disease activity by intestinal biopsy performed during endoscopy in association with endoscopic scoring systems. Both radiology and endoscopy are conventional for the diagnosis of inflammatory bowel disease (IBD). However these techniques have severe limitations when it comes to assessing functional components of the disease such as activity and prognosis. Here we briefly review the value of two emerging intestinal function tests. Intestinal permeability, although ideally suited for diagnostic screening for small bowel Crohn’s disease, appears to give reliable predictive data for imminent relapse of small bowel Crohn’s disease and it can be used to assess responses to treatment. More significantly it is now clear that single stool assay of neutrophil specific proteins (calprotectin, lactoferrin) give the same quantitative data on intestinal inflammation as the 4-day faecal excretion of 111Indium labelled white cells. Faecal calprotectin is shown to be increased in over 95% of patients with IBD and correlates with clinical disease activity. It reliably differentiates between patients with IBD and irritable bowel syndrome. More importantly, at a given faecal calprotectin concentration in patients with quiescent IBD, the test has a specificity and sensitivity in excess of 85% in predicting clinical relapse of disease. This suggests that relapse of IBD is closely related to the degree of intestinal inflammation and suggests that targeted treatment at an asymptomatic stage of the disease may be indicated.

Clinical mutations in the L1 neural cell adhesion molecule affect cell-surface expression

Mutations in the L1 neural cell adhesion molecule, a transmembrane glycoprotein, cause a spectrum of congenital neurological syndromes, ranging from hydrocephalus to mental retardation. Many of these mutations are single amino acid changes that are distributed throughout the various domains of the protein. Defective herpes simplex virus vectors were used to express L1 protein with the clinical missense mutations R184Q and D598N in the Ig2 and Ig6 extracellular domains, respectively, and S1194L in the cytoplasmic domain. All three mutant proteins were expressed at similar levels in infected cells. Neurite outgrowth of cerebellar granule cells was stimulated on astrocytes expressing wild-type or S1194L L1, whereas those expressing R184Q and D598N L1 failed to increase neurite length. Live cell immunofluorescent staining of L1 demonstrated that most defective vector-infected cells did not express R184Q or D598N L1 on their cell surface. This greatly diminished cell-surface expression occurred in astrocytes, neurons, and non-neural cells. In contrast to wild-type or S1194L L1, the R184Q and D598N L1 proteins had altered apparent molecular weights and remained completely endoglycosidase H (endoH)-sensitive, suggesting incomplete post-translational processing. We propose that some missense mutations in human L1 impede correct protein trafficking, with functional consequences independent of protein activity. This provides a rationale for how expressed, full-length proteins with single amino acid changes could cause clinical phenotypes similar in severity to knock-out mutants.

Behavioural disturbances associated with hyperdopaminergia in dopamine-transporter knockout mice

Mice lacking the dopamine transporter (DAT-/-) are characterized by high extracellular dopamine levels and spontaneous hyperlocomotion. We performed a detailed analysis of the behavioural phenotype of DAT-/- mice in order to identify other behavioural impairments associated with the hyperdopaminergic tone of these mutant mice. In particular, we investigated locomotor activity, exploration, and social and maternal behaviours, which are known to be regulated by dopamine. DAT-/- mice were easily aroused by novelty and always responded with hyperlocomotion, which interfered with habituation to the testing environment, exploratory behaviour in an open field and the coping response to forced swimming stress. Social behaviours such as interaction with an unknown congener or aggressiveness were not modified in DAT-/- mice compared with DAT+/- and DAT+/+ mice, although the maternal behaviour of mutant females was severely disturbed. Haloperidol and clozapine reversed the hyperactivity in DAT-/- mice, with a rightward shift of the dose-response curve compared with control animals, suggesting a dopamine-mediated effect. These results emphasize the role of dopamine regulation in locomotion, exploration and maternal behaviours and suggest that mice with a genetic deletion of DAT may represent a useful model to elucidate the altered behavioural processes accompanying pathological conditions associated with hyperdopaminergic function.

Increased rewarding properties of morphine in dopamine-transporter knockout mice

The activation of dopamine (DA) neurotransmission plays a crucial role in the behavioural responses to drugs of abuse. In particular, increased extracellular levels of DA within the mesolimbic pathway have been implicated in the rewarding and locomotor stimulatory properties of morphine. We investigated the behavioural responses to morphine in mice with a genetic disruption of the DA transporter (DAT), resulting in a constitutively high level of extrasynaptic DA. In the conditioned place preference test, DAT-/- mice exhibited a stronger rewarding response to morphine (5 mg/kg, s.c.) compared with control littermates. However, the same dose of morphine failed to increase locomotor activity in DAT-/- mice, whilst enhancing locomotion in DAT+/- and DAT+/+ animals. Morphine-induced analgesia was unaffected in mutant mice, but the behavioural expression of naloxone-induced withdrawal signs was blunted. In vivo voltammetry in the shell of the nucleus accumbens revealed that morphine was able to stimulate DA neurons in DAT-/- mice, resulting in the accumulation of higher extracellular DA levels compared with control animals. Morphine also induced a higher rate of c-fos transcription in the shell of the nucleus accumbens in mutant mice. We conclude that morphine-induced rewarding responses are firmly established in DAT mutant mice despite a DA transmission that is already tonically activated, and independently of any effect on locomotion. These particular behavioural responses to morphine may be associated with the action of the drug on DA release and c-fos expression in the shell of the nucleus accumbens of DAT-/- mice.

The membrane glycoprotein G1 of Uukuniemi virus contains a signal for localization to the Golgi complex

Members of the Bunyaviridae family acquire their envelopes by budding into the Golgi complex (GC). The accumulation of the membrane glycoproteins G1 and G2 in the GC probably determines the site of maturation. Here we have studied the intracellular transport and targeting to the GC of G1 and G2 of Uukuniemi virus, a member of the Phlebovirus genus, and report on their expression from cloned cDNAs either together or separately by using a T7 RNA polymerase-driven vaccinia virus expression system. When G1 and G2 were expressed together from a full-length cDNA as the p110 precursor, both proteins were localized to the Golgi complex, as evidenced by colocalization with the Golgi marker enzyme mannosidase II. Immunofluorescent staining indicated that G1 expressed alone also localized to the GC. However, pulse-chase experiments showed that G1 remained endoglycosidase H sensitive. G2 expressed alone remained associated with the endoplasmic reticulum (ER). G2 could be rescued from the ER and transported to the GC by coexpression with G1 from separate mRNAs. Coexpression also increased the efficiency of G1 transport to the GC. With none of the constructs could the glycoproteins be observed on the cell surface. These results show that efficient export of G1 and G2 from the ER requires coexpression of both proteins, in conformity with our previous results showing that G1 and G2 form heterodimeric complexes in the ER. Since G1 expressed alone is retained in the GC, we conclude that G1 contains a retention signal for localization to the GC. G2 might thus become associated with the GC indirectly via its interaction with G1.

Cell biology of viruses that assemble along the biosynthetic pathway

In this review we discuss five groups of viruses that bud into, or assemble from, different compartments along the biosynthetic pathway. These are herpes-, rota-, corona-, bunya- and pox-viruses. Our main emphasis will be on the virally-encoded membrane glycoproteins that are responsible for determining the site of virus assembly. In a number of cases these proteins have been well characterized and appear to serve as resident markers of the budding compartments. The assembly and dissemination of these viruses raises many questions of cell biological interest.

The molecular basis of codominant expression of the histocompatibility-2 genetic region

H-2 alloantigens in an intact, undegraded form can be solubilized by the nonionic detergent NP-40 and isolated by indirect immunoprecipitation and electrophoresis in sodium dodecyl sulfate on polyacrylamide gels. With the use of an immunological precipitation method, the question about the number of cellular H-2 gene products in heterozygous cells has been partially resolved. At least four separable gene products were detected in cells heterozygous at the H-2 genetic region-one for each of the H-2D genes of the two parental haplotypes, and one for each of the H-2K genes of the two parental haplotypes. This is in contrast to the two H-2 gene products reported previously for cells homozygous at the H-2 region. The findings establish that the two parental H-2 haplotypes on homologous chromosomes in heterozygous cells are ultimately expressed as different glycoprotein molecules.

Spin-labeled electron spin resonance study of the lipid-containing membrane of influenza virus

The organization of the lipid-containing membrane of influenza virus has been studied by the use of three different lipid spin labels, and the results are compared with a parallel study on human erythrocyte ghosts. The lipid phase of the viral membrane is slightly more rigid than that of the erythrocyte ghosts. The data suggest that the viral lipid is arranged in a bilayer. The data suggest that the viral lipid is arranged in a bilayer. The glycoprotein spikes covering the viral membrane were specifically removed by proteases, and no alteration in the environment of any of the three spin labels was detected. This suggests that the spikes are not involved in determining the organization of the lipid bilayer.