A protein assay based on colloidal gold conjugates with trypsin

The standard sol particle immunoassay (SPIA) is based on a biospecific aggregation of gold nanoparticle conjugates, followed by conventional spectrophotometry. Here we propose a novel SPIA format that uses microtitration immunological plates and an enzyme-linked immunosorbent assay reader. The novel and standard assays are exemplified by determination of immunoglobulin G by using 15-nm colloidal gold-protein A conjugates. We also describe a novel sol particle-trypsin assay using conjugates of gold nanoparticles with trypsin. The method is based on measuring spectral extinction changes caused by the addition of protein to a conjugate solution. The changes in the extinction spectra are presumed to be related to aggregation of gold nanoparticles caused by polyvalent binding of protein molecules to the trypsin molecules of the conjugates.

Detection of plant viruses using a surface plasmon resonance via complexing with specific antibodies

The use of instrumental systems based on the surface plasmon resonance (SPR) for rapid diagnosis of intact plant viruses (in particular, tobacco mosaic virus (TMV)) is considered. A new approach using detection of viral antigen and antibody (IgG) complexes formed during the preincubation step (instead of their consecutive application in classical approach) is discussed. A comparison between signal level registered from the mixture of virus and specific serum and that from the sample without virus (samples deposited onto the sensor surface treated with thiocyanate and protein A Staphylococcus aureus) allows unambiguous detection of viral particles in the material studied. The performance capabilities of the method are discussed and illustrated by quantitative detection of virus in the actual samples (cells homogenate) at high concentration.

Engineering the hepatocyte differentiation-proliferation balance by acellular cadherin micropresentation

The successful development of bioartificial and cell-based liver support systems relies on the identification of molecular mechanisms controlling the balance between hepatocellular proliferation and differentiation. Although a definitive function-inductive role for the cell-cell adhesion molecule, E-cadherin, was established through lateral cadherin-cadherin engagement in hepatocyte cocultures (Brevia, T.A., and Moghe, P.V. Biotechnol. Bioeng. 76, 295, 2001), the roles of other modes of cadherin presentation are not well understood. Further, alternative cadherin display configurations promoting cell growth/proliferative pathways, a major requisite for sustainable engineered tissues, remain to be identified. In this report, we employed protein A-functionalized polymeric microsphere substrates that specifically bound self-dimerizing cadherin-IgG/Fc fusion chimeras via their Fc regions, thereby orienting them outward for active adhesion, and presented the E-cadherin chimeras basally to cultured rat hepatocytes to study the effects of cadherin display on cell proliferative potential and differentiated function. In contrast to the previously documented function-inductive roles of laterally expressed cadherin, basal acellular cadherin presentation resulted in an increase in hepatocyte DNA synthesis and cell divisions, accompanied by a decrease in the expression of a key marker of liver-specific function, albumin message levels. Next, we probed the relative effect of basal exogenous display of acellular cadherins on the inductive phase of differentiation within hepatocyte cocultures with cadherin-expressing L929 cells. When acellular cadherins were applied to hepatocyte cocultures involving chaperone cell-mediated cadherin presentation, the previously reported function-inductive effects of cadherins on hepatocyte function were reversed, resulting in lower levels of albumin and urea secretion indicating a dominance of acellular cadherin effects. Our results demonstrate that cadherins are important regulators of the balance between hepatocyte differentiation and proliferation, and furthermore that the direction of balance shift may be dependent on the method of cadherin presentation. Thus, the geometric display of cadherin could be a potential parameter to switch hepatocyte functional-proliferative balance and may aid in customizing scaffolds for regulating hepatic tissue dynamics.

Proteinuria in rats induced by serum from patients with collapsing glomerulopathy

BACKGROUND

Primary collapsing glomerulopathy recurs postransplant, raising the possibility of circulating factors implicated in the pathogenesis of the disease.

METHODS

To determine the presence of circulating factors in collapsing glomerulopathy patients, we tested serum from those patients in an in vivo assay. Eleven groups of rats received serum from collapsing glomerulopathy patients, idiopathic focal segmental glomerulosclerosis (FSGS) or healthy subjects in its native form, isolated IgG, or serum without IgG. The presence of proteinuria and creatinine clearance were determined. Histopathologic analysis included light, immunofluorescence, and electron microscopy.

RESULTS

Collapsing glomerulopathy rats developed proteinuria while rats injected with serum from FSGS and healthy subjects did not. Rats injected with serum of collapsing glomerulopathy in its native form developed marked proteinuria (99.2 +/- 42 mg/24 hours at day 5, P= 0.0001, compared to the baseline), and decreased in creatinine clearance. Rats receiving isolated IgG or serum without IgG from collapsing glomerulopathy developed mild proteinuria (46.5 +/- 8.4 mg/24 hours and 30.9 +/- 11 mg/24 hours, respectively, at day 5 (P= 0.0001). Glomerular tuft retraction and podocyte damage were seen only in collapsing glomerulapthy rats. No abnormalities were found in rats injected with serum from FSGS or healthy subjects.

CONCLUSION

Circulating factors in the serum of collapsing glomerulopathy patients produce podocyte damage, whereas such factors are not present in noncollapsing FSGS. IgG eluates from collapsing glomerulopathy produce proteinuria when injected into the rat. Such factors remain in the circulation when serum of patients is adsorbed into protein A, raising the possibility that there are more than one circulating factor present in patients with collapsing glomerulopathy.

Vascularization and perfusion of hepatocellular carcinoma: assessment with contrast-enhanced ultrasound using perflutren protein-type A microspheres

PURPOSE

To assess the vascularization and the perfusion within hepatocellular carcinoma (HCC) including treatment-related changes with contrast-enhanced (CE) ultrasound (US).

MATERIALS AND METHODS

Twenty-six biopsy-verified HCC lesions (size between 2.5-8 cm, median 3.8 cm) in 20 patients were examined with unenhanced and CE vascular US techniques immediately before selective angiography for transarterial chemoembolization (TACE) as well as immediately after TACE using all of the following modalities: color-coded Doppler sonography (CCDS), power Doppler imaging (PDI), CE pulse inversion harmonic imaging with PDI (PIHI+PDI), and CE coded harmonic angiography (CHA). In CE US studies, perflutren protein-type A microspheres were administered as contrast agent in a single 0.5 ml i.v. bolus diluted in 20 ml 0.9% NaCl. Selective arteriograms and CE computed tomographies were taken for reference purposes. The Wilcoxon test was used for statistical analysis.

RESULTS

Intratumoral vessels could be visualized before TACE in 11/26 lesions (42%) with CCDS; in 15/26 (58%) with PDI; in 23/26 (88%) with CE CHA; in 26/26 (100%) with CE PIHI+PDI. Following TACE, the sensitivities were calculated as follows: CCDS 33%; PDI 55%; CE CHA 77%; and CE PIHI+PDI 100%. The corresponding negative predictive values were 74% for CCDS; 81% for PDI; 89% for CE CHA and 100% for CE PIHI+PDI. During the capillary phase, contrast enhancement could be observed in the CHA mode only.

CONCLUSION

CE US by means of PIHI+PDI and CHA enables reliable visualization of residual tumor following TACE equivalent to that which is attained with angiography and Contrast Harmonic Imaging with Power Doppler, if perflutren microspheres are used as contrast agent in a single low-dose bolus.

ChIC and ChEC; genomic mapping of chromatin proteins

To map the genomic interaction sites of chromatin proteins, two related methods were developed and experimentally explored in Saccharomyces cerevisiae. The ChIC method (chromatin immunocleavage) consists of tethering a fusion protein (pA-MN) consisting of micrococcal nuclease (MN) and staphylococcal protein A to specifically bound antibodies. The nuclease is kept inactive during the tethering process (no Ca2+). The ChEC method (chromatin endogenous cleavage) consists of expressing fusion proteins in vivo, where MN is C-terminally fused to the proteins of interest. The specifically tethered nucleases are activated with Ca2+ ions to locally introduce double-stranded DNA breaks. We demonstrate that ChIC and ChEC map proteins with a 100-200 bp resolution and excellent specificity. One version of the method is applicable to formaldehyde-fixed nuclei, another to native cells with comparable results. Among various model experiments, these methods were used to address the conformation of yeast telomeres.

Characterization of protein-DNA association in vivo by chromatin immunoprecipitation

Chromatin immunoprecipitation (ChIP) is one of the most powerful methods to identify and characterize the association of proteins with specific genomic regions in the context of intact cells. In this method, cells are first treated with formaldehyde to crosslink protein-protein and protein-DNA complexes in situ. Next, the crosslinked chromatin is sheared by sonication to generate small chromatin fragments, and the fragments associated with the protein of interest are immunoprecipitated using antibodies to the protein. Finally, protein-DNA crosslinks are reversed and the DNA is examined for the presence of particular sequences by quantitative polymerase chain reaction (PCR). Enrichment of specific sequences in the precipitate indicates that the sequences are associated with the protein of interest in vivo. The ChIP method described here is intended for studying protein-DNA association in the budding yeast Saccharomyces cerevisiae, but it can be easily implemented in other cell types, including fly, mammalian, and plant cells.

A proteome-wide approach identifies sumoylated substrate proteins in yeast

The ubiquitin-related protein SUMO-1 is covalently attached to proteins by SUMO-1 ligases. We have performed a proteome-wide analysis of sumoylated substrate proteins in yeast. Employing the powerful affinity purification of Protein A-Smt3 (Smt3 is the yeast homologue of SUMO-1) from yeast lysates in combination with tandem liquid chromatography mass spectrometry, we have isolated potential Smt3-carrying substrate proteins involved in DNA replication and repair, chromatin remodeling, transcription activation, Pol-I, Pol-II, and Pol-III transcription, 5' pre-mRNA capping, 3' pre-mRNA processing, proteasome function, and tubulin folding. Employing tandem affinity purifications or a rapid biochemical assay referred to as "SUMO fingerprint," we showed that several subunits of RNA polymerases I, II, and III, members of the transcription repression and chromatin remodeling machineries previously not known to be sumoylated, are modified by SUMO-1. Thus, the identification of a broad range of SUMO-1 substrate proteins is expected to lead to further insight into the regulatory aspects of sumoylation.

Protein A/G dependent ELISA a promising diagnostic tool in Lyme disease seroprevalence in game animals and hunting dogs

One of the major problems in serodiagnosis in wild animals is unavailability of specific antiglobulin conjugate. Our study focuses on validation of Protein A/G dependent ELISA in game animals like deer and mouflons as well as in hunting dogs. Binding ability of Protein A/G-conjugate to antibodies was the highest in dogs followed by fallow deer and mouflons. Three different whole cell Borrelia antigens were used to evaluate antigen dependent variation. In new Protein A/G-ELISA the highest sensitivities (90.50%, deer; 85.37%, mouflon & 94.29%, dog) were obtained by B. garinii antigen, with no statistically significant variation (chi(2), P>0.05) among all other antigens used. Average seroprevalences observed in deer, mouflons and dogs were 44.90%, 29.41% and 30.43%, respectively. Marked influence of age on seroprevalence was noticed. Protein A/G-ELISA proved to be sensitive and promising diagnostic tool in serodiagnosis of Lyme disease in game ungulates and it can be used effectively for serosurvey in different wild mammals.

Absence of protein G-Fc interaction in ficin-derived mouse IgG1 digests

Typical procedure for IgG fragmentation is based on proteolytic cleavage at the hinge region and usually involves a post-digestion purification step. In mice, IgG1 has been found to bind poorly to protein A. As a result, protein G chromatography could be considered as an alternative for Fc removal. Protein G is generally expected to bind specifically to the Fc region of IgG, but applying protein G for the purification of Fab2 fragment of mouse monoclonal IgG1 under standard physiological conditions, we obtained reproducible clone-independent negligible protein G-Fc reactivity and strong protein G-Fab2 interaction.

Detection of pneumolysin in cerebrospinal fluid for rapid diagnosis of Pneumococcal meningitis

BACKGROUND & OBJECTIVES

Pneumolysin, a toxin produced by Streptococcus pneumoniae is associated with virulence and is found in all invasive isolates. Its role as a diagnostic tool has recently been exploited. Most of the methods used are based on molecular techniques and are not cost-effective. The present study was undertaken to evaluate a simple, rapid and cost-effective method to detect pneumolysin in CSF as a diagnostic test for pneumococcal meningitis.

METHODS

A total of 75 CSF samples from children with presumptive diagnosis of acute pyogenic meningitis or encephalitis were subjected to Gram stain, culture and pneumolysin detection by Cowan 1 staphylococcal protein A co-agglutination technique.

RESULTS

Pneumolysin was detected in 26(78.8%) of 33 culture proven CSF samples and 4(9.5%) of 42 culture negative samples. Antigen detection by Co-A had a specificity of 90 per cent and a sensitivity of 79 per cent when compared with culture. Compared to Gram stain, pneumolysin Co-A had a specificity and sensitivity of 91.0 and 92.0 per cent respectively.

INTERPRETATION & CONCLUSION

Detection of pneumolysin was found to be a simple, low cost antigen detection assay for rapid diagnosis of pneumococcal meningitis, for routine use in the developing countries.

A protein A-based orientation-controlled immobilization strategy for antibodies using nanometer-sized gold particles and plasma-polymerized film

A novel protein A (PA)-based strategy for the orientation-controlled immobilization of antibodies using nanometer-sized gold (Nano-gold) particles and an amine-terminated plasma-polymerized film (PPF) has been proposed. A quartz crystal microbalance was fabricated, accordingly, coupling with haptoglobin (HP) antibody followed by HP immunoassay, as a model test system. The crystal was modified with plasma-polymerized n-butyl amine film to deposit Nano-gold particles and PA, on which HP antibodies were immobilized. The surface topology of the as-prepared crystal was characterized by use of scanning electron microscopy. In contrast to the traditional flat gold surface, the assembled Nano-gold particle monolayer could allow PA molecules bound with higher bioactivity and loading amount (density), achieving better antibody-binding capabilities. Results indicate that immunosensors prepared using the developed PPF-Nano-gold-PA binding procedure exhibit increased analytical performance compared with those produced using the direct PA binding procedure and the PPF-based glutaraldehyde cross-linking procedure. A HP serum concentration as low as 0.41 nM can be determined by this new system. Regenerated simply by rinsing in the acid buffer, the proposed sensor can achieve up to 11 assay cycles without significant loss of sensitivity.

Affinity fractionation of lymphocytes using a monolithic cryogel

A new type of continuous, supermacroporous, monolithic, cryogel affinity adsorbent was developed, allowing specific fractionation and separation of human peripheral blood lymphocytes in a chromatographic format. The affinity adsorbent was used to design a novel cell separation strategy, which was based on the interaction of protein A from Staphylococcus aureus with cells bearing IgG antibodies on the surface. After treating lymphocytes with goat anti-human IgG(H+L), the IgG-positive B-lymphocytes were efficiently separated from T-lymphocytes. Protein A covalently coupled to epoxy activated dimethylacrylamide (DMAA) cryogel matrix specifically bound IgG-bearing B-lymphocytes through the Fc region, while non-bound T-lymphocytes passed through the column. More than 90% of the B-lymphocytes were retained in the column while the cells in the breakthrough fraction were enriched in T-lymphocytes (81%). The viability of the T-lymphocytes isolated was greater than 90%. The bound lymphocytes released by human or dog IgG recovered 60-70% of the B-cells without significantly impairing the cell viability. The technique can be applied in general to cell separation systems where IgG antibodies against specific cell surface markers are available.

[Detection of circulating antigen in urine from mice infected with Toxoplasma tachyzoites by SPA-ELISA]

OBJECTIVE

To explore a simple and convenient immunoassay for early diagnosis of Taxoplasma infection.

METHODS

Urine samples collected from three groups of mice infected with different doses of tachyzoites were detected for Taxoplasma circulating antigen (TCA) by dot-ELISA using HRP-SPA as a second antibody (SPA-ELISA).

RESULTS

Taxoplasma circulating antigens were detected in all three groups of infected mice in contrast with the normal control group. Taxoplasma circulating antigen was detected on d6 and d3 after infection in mice of light- and moderate-infection groups, respectively.

CONCLUSION

SPA-ELISA is a simple and convenient method for early immunodiagnosis of recent Taxoplasma infection.

[Investigation of interaction of immunoglobulins and detection of viral antigens in cell homogenates by the surface plasmon resonance method]

Immobilization of immunoglobulins on the unmodified gold surface and the gold surface, modified by thiocyanate and protein A Staphylococcus aureus and their subsequent interaction with complementary antibodies were studied using the surface plasmon resonance method. Viral antigens were detected by surface plasmon resonance method in the cell homogenate of green alga Bracteococcus minor, which was artificially infected by tobacco mosaic virus. It was shown, that the process of interaction between virus and antiviral serum obey the Langmure model.

Design and scaleup of downstream processing of monoclonal antibodies for cancer therapy: from research to clinical proof of principle

Murine monoclonal antibodies (mAb) from cell culture supernatants have been purified in order to acquire clinical grade for in vivo cancer treatment. The starting material was purified by high performance liquid chromatography (HPLC) systems ranging from the analytical scale process to a scaleup to 1 g per batch. Three columns (Protein A affinity chromatography with single-step elution, hydroxyapatite (HA) chromatography followed by linear gradient elution and endotoxin removing-gel chromatography), exploiting different properties of the mAb were applied. The final batches of antibody were subjected to a large panel of tests for the purpose of evaluating the efficacy of the downstream processing. The resulting data have allowed us to determine the maximum number of times the column can be used and to precisely and thoroughly characterize antibody integrity, specificity, and potency according to in-house reference standards. The optimized bioprocessing is rapid, efficient, and reproducible. Not less importantly, all the techniques applied are characterized by costs which are affordable to medium-sized laboratories. They represent the basis for implementing immunotherapeutic protocols transferable to clinical medicine.

Rapid polyelectrolyte-based immunofiltration technique for testosterone detection in serum samples

A new immunofiltration assay for testosterone is proposed. During the first step of the assay, testosterone molecules in serum samples compete in solution with the testosterone-peroxidase conjugate for interaction with anti-testosterone antibodies pre-bound to the conjugate between staphylococcal protein A and polymethacrylate polyanion. The reaction mixture is then filtered through a membrane charged with immobilized poly(N-ethyl-4-vinylpyridinium) polycation. The filtration is accompanied by a rapid separation of the polyanion containing complexes due to high-affinity electrostatic interactions. Following removal of unbound compounds the immobilized peroxidase is detected using a substrate that produces an insoluble coloured product. The proposed assay has been shown to combine high speed (20 min) and sensitivity (0.1 ng ml(-1)), and to be applicable for out-of-laboratory conditions. Based on densitometric measurements, the RSD of the assay is calculated to be 3.2-5.1% (n = 4). The proposed assay is 4 times faster than the microplate enzyme immunoassay (ELISA) based on the same immunoreagents. Pre-incubation of the antibody and the polyanion-protein A conjugate at a certain ratio excludes the influence of immunoglobulins from the tested serum samples on the assay results. The polyanion-protein A conjugate can be used as a universal reagent, eliminating the necessity to modify specific antibodies for each immunoassay.

[A rapid procedure to purify serum IgG from Microtus fotis]

OBJECTIVE

To evaluate the procedure to purify IgG antibodies from Microtus fotis serum.

METHODS

IgG antibodies from sera of three groups of Microtus fotis were purified by protein G or protein A affinity chromatography, their purity and binding capacity were compared.

RESULTS

The protein G affinity chromatography was more efficient than protein A affinity chromatography. The antibodies isolated from protein G affinity chromatography showed a higher purity and better activity than that from protein A affinity chromatography monitored by SDS-PAGE and ELISA. The ability of the purified IgG to bind the second antibodies were 8.5 times and 3.1 times that of non-IgG proteins and unpurified sera, respectively.

CONCLUSION

The protein G affinity chromatography is a rapid, convenient and reliable procedure for Microtus fotis serum IgG purification.

Protein A immunoadsorption in a pregnant woman with habitual abortion

The role of antibodies in the occurrence of recurrent spontaneous miscarriage is well known. However there are many controversial issues in the management of habitual abortion. This paper describes the effect of Protein A immunoadsorption on serum levels of these antibodies and its impact on a case of a successfully treated woman in a outpatient department without need for a central venous catheter. Given the favourable clinical results described in our paper we think it may be relevant for some worse cases in clinical practice and will interest your readers.

Comparison of techniques for monitoring antibody fragment production in E. coli fermentation cultures

The use of an optical biosensor for monitoring antibody fragment accumulation following induction in a batch fermentation of recombinant E. coli is compared to the more traditional method of ELISA quantification. Using the biosensor, concentration data can be obtained within minutes of sample addition to the device, compared to an average assay time of 3-4 h for the ELISA. We describe two biosensor assays developed as an alternative to ELISA and compare them with ELISA in the ability to provide quantitative product accumulation profiles during fermentation. Discrepancies in titers recorded by the assays are explained by a combination of differences in product variants detected by each assay and interference from sample contaminants. Method of sample preparation is also shown to be important if accurate concentration data is required. Both biosensor assays are shown to be capable of providing product accumulation profiles comparable to those obtained by ELISA. The use of a rapid extraction technique would allow such data to be obtained during process operation, enabling improved fermentation control and more rapid process development.

Hypotensive reaction during staphylococcal protein A column therapy in a patient with anomalous degradation of bradykinin and Des-Arg9-bradykinin after contact activation

BACKGROUND

Hypotensive reactions have occurred in patients taking angiotensin converting enzyme (ACE) inhibitors after infusion of blood previously in contact with negatively charged surfaces capable of generating kinins, which accumulate when ACE, a kininase, is inhibited. A patient with anomalous bradykinin (BK) metabolism who experienced hypotension during extracorporeal staphylococcal protein A (SPA) therapy while on an ACE inhibitor was studied.

CASE REPORT

A patient with mitomycin-associated hemolytic-uremic syndrome received SPA treatments after her ACE inhibitor, lisinopril, was held. Lisinopril was restarted before her 18th SPA treatment, and immediately after return of treated plasma she developed facial redness and hypotension, which resolved after the return stopped and recurred when restarted. To study formation and degradation of kinins, exposed her plasma to glass beads. We found a normal kinin formation rate but an abnormal degradation and accumulation of Des-Arg9-BK. The kinin degradation enzymes ACE, aminopeptidase P (APP), and carboxypeptidase N (CPN) were measured while on an ACE inhibitor, showing absence of ACE activity, low APP, but normal CPN.

CONCLUSION

This patient's vasodilation and hypotension during SPA therapy was associated with a pre- existing anomaly of BK metabolism. Her ACE inhibitor shifted degradation toward Des-Arg9-BK formation, and her low APP was associated with a prolonged t50 and accumulation of the vasoactive Des-Arg9-BK.

Study on the scale-up of human IgG3 purification using protein A affinity chromatography

The purification of human IgG3 subclass out of IgG (Immunoglobulin-G) was studied using protein A-Sepharose affinity chromatography. The effect of operational parameters such as flow rate, ionic strength, pH and size of sample was investigated, and the process was scaled-up 10-fold. The use of 0.5 m NaCl in the loading buffer had a dramatic effect in the purity of IgG3 recovered in the flowthrough fraction (values in the order of 97% were consistently obtained). This was attributed to a more effective binding of IgG subclasses 1, 2 and 4 to protein A (well known classical mechanism based in Fc fragment) and in some extent to a decrease in the binding of subclass 3 to protein A by the alternative mechanism based in the Fab fragment. The increase in residence time also increased in a relevant way the purity of IgG3. This is attributed to an increased effectiveness of the mechanisms mentioned above. The recovery yields in the IgG3 rich fraction were in the range 21-32% and are possibly a consequence of binding to protein A by the alternative mechanism and also due to deactivation during processing.