Assessment of a method for immunochemical detection of antigen on nitrocellulose membranes

Detección inmunoquímica de la adulteración de chorizo de cerdo con proteínas de soja

Rabbit polyclonal antisera were produced against soy flour proteins extracted with 0.5 M NaCl solution and purified by affinity chromatography to detect adulteration in pork chorizo (sausage) with an enzyme-linked immunoabsorbent assay (ELISA). To detect adulteration the following saline extracts were prepared: 100% pork and 100% soy chorizo and mixtures of these two pro ducts (90:10, 80:20, 70:30, 60:40, 50:50, 40:60, 30:70, 20:80, 10:90), and extracts of two commercial chorizos labeled as pork. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed that the salt solution was the most suitable for protein extraction compared to water and a 1% SDS solution. The commercial chorizos did not have the characteristic electrophoretic pattern for pork chorizos. The antibodies were specific for soy and its products, as there was no response to other vegetable and animal proteins by gel immunodiffusion assay or ELISA. The standard curve obtained with the ELISA results of the chorizo mixtures gave a correlation coefficient of r2 = 0.988. The two commercial chorizo values resulted in a 32 and 40% soy substitution. Total time for ELISA was optimized to 4 h, and 2 h if the plates were previously activated with the antigen. Variation coefficients of ELISA readings for replicates of the same extract in one plate and variation of different assays on different days were 2.3 and 8% respectively.

Differential activation and inhibition of human platelet thrombin receptors by structurally distinct α-, β- and γ-thrombin

The development of drugs to neutralize the action of thrombin has to date focused on the alpha form of the protease. It is generally agreed that inactive prothrombin is proteolytically converted to active alpha-thrombin which may be further hydrolyzed to beta- and gamma-thrombin. While all three forms of the enzyme retain catalytic activities, only alpha-thrombin is presumed to be physiologically important. The beta- and gamma-thrombin are presumed to be degradation products of no physiological significance. Our demonstration that beta- and gamma-thrombin selectively activate PAR-4 in this and a previous report (J. Biol. Chem. 276, 21173-21183, 2001) necessitates a reevaluation of how we view their physiological roles and how we approach the pharmacological regulation of their actions. Beta-thrombin, like gamma-thrombin, at nM levels selectively activates PAR-4. This was demonstrated by full retention of aggregatory activity with platelets whose PAR-1 and GP Ib receptors were inactivated. Furthermore, the beta-thrombin response was abrogated by desensitizing platelets with suboptimal levels of the thrombin receptor activating peptide for PAR-4 (TRAP-4). For beta-thrombin and gamma-thrombin to have a physiological role, it is necessary to show they can be generated under physiological conditions. We demonstrate, for the first time, that alpha-thrombin is hydrolyzed in less than 1 min by activated factor X at physiological pH, in vitro. This implies that alpha-thrombin may be rapidly converted to beta-thrombin and/or gamma-thrombin in vivo in the proper microenvironment. The differential activation of the three platelet thrombin receptors by alpha-, beta- and gamma-thrombin implies selective structural variations between these thrombin species. Structural differences are likely to account for the marked differential responses observed with the antithrombotic, hirudin, which inhibits alpha-thrombin , is a slightly weaker inhibitor of beta-thrombin and a very weak inhibitor of gamma-thrombin -induced platelet aggregations. The converse order of inhibition is observed with the physiological protease inhibitor, alpha(1)-antitrypsin. Finally, a non-traditional inhibitor, histone-1, selectively inhibits only beta- and gamma-thrombin , primarily at the receptor level of PAR-4 rather than on the thrombin molecule. Trypsin, like beta- and gamma-thrombin , activates PAR-4 and is also inactive with TRAP-4 desensitized platelets. Therefore, it was reasoned that trypsin would be more structurally similar to gamma-thrombin than to alpha-thrombin. The analysis of the crystalline structures of alpha-, gamma-thrombin and trypsin from the databases confirm that this is the case. These findings should help to elucidate structure-function relationships of the different thrombins and may aid in the development of new anti-thrombotic drugs.

A strategy for identifying serodiagnostically relevant antigens of Leishmania or other pathogens in genetic libraries

Different individuals, when infected with the same parasite, rarely produce antibodies against the same set of antigens. Indeed, unless a particular antigen happens to be recognized by antibodies in all individuals, the use of a single antigen in the serodiagnosis of parasitic diseases leads, invariably, to false-negative results. A straightforward method for pin-pointing, in genetic libraries, the precise antigens that would increase serodiagnostic assay sensitivities is presented. The method is based on the utilization of sera that produced false-negative results against previously available antigens. Employing this false-negative serum-selection methodology for the identification of new Leishmania infantum recombinant antigens (rAgs), the sensitivity of a dipstick assay for anti-Leishmania antibodies in a panel of sera from patients with visceral leishmaniasis was increased from 83.3% to 98.1%, without affecting its specificity, by the inclusion of a fifth and a sixth L. infantum rAg.

Cell biology of cytochrome P-450 in the liver

Cytochromes P-450 (P-450) are members of a multigene superfamily of hemoproteins consisting the microsomal monooxygenase system with NADPH P-450 reductase (reductase) and/or reducing equivalents. Expression of many P-450 isoforms in hepatocytes is shown to be regulated at the level of transcription through interaction between cis-acting elements in the genes and DNA-binding (transacting) factors. Some isoforms of the CYP1A, 2B, 2E, and 3A subfamilies are regulated at the posttranscriptional level. For the topology of P-450 and reductase molecules in ER membrane of hepatocytes, models from stopped flow analysis and electron spin resonance are proposed. The densities of total P-450 and reductase molecules are revealed to be high enough to support the cluster model, suggesting that about ten P-450 molecules form an aggregate and surround one reductase molecule, and therefore the two enzymes form large micelles. ER proliferation after PB administration, which had been correlated with increase in P-450 level, is shown to be probably independent of the increase in P-450 level. There are considerable discrepancies among results reported on sublobular expression of various P-450 isoforms. Causes of the discrepancies are likely to be differences in experimental conditions of histochemical detection carried out and/or in species, strain, and/or sex.

Nuclear factor-90 of activated T-cells: A double-stranded RNA-binding protein and substrate for the double-stranded RNA-dependent protein kinase, PKR

NFAT transcription factors play a central role in initiating T-cell activation through the induction of immediate-early T-cell specific genes including interleukin-2 (IL-2). NFAT transcription factors bind to a sequence in the IL-2 enhancer known as the antigen receptor response element 2 (ARRE-2). Multiple proteins exhibiting ARRE-2 binding activity have been isolated, including a heterodimer from stimulated T-cell nuclear extracts consisting of Mr = 90 000 (NF90) and Mr = 45 000 (NF45) subunits. The subunits of this heterodimer have been cloned, and NF90 was found to encode a protein containing two domains that are predicted to form motifs capable of binding to double-stranded RNA. Using in vitro translated polypeptides, we have demonstrated that NF90 specifically binds to double-stranded RNA. Furthermore, NF90 was phosphorylated in a double-stranded RNA-dependent manner likely by the interferon-induced, double-stranded RNA-dependent protein kinase, PKR. The NF90 protein was found to be expressed not only in T-cells, but also in nonimmune HeLa cells. In HeLa cells, the protein was almost exclusively localized to the ribosome salt wash fraction of cell lysates.

Immunological and functional properties of the exudate gum from northwestern Mexican mesquite (Prosopis spp.) in comparison with gum arabic

A comparison between the fine structural features of exudate gum from mesquite (Prosopis spp.) indigenous to NW Mexico and commercial gum arabic from Acacia spp. was achieved by means of immunological techniques. Their functional properties were compared from the ability to form oil-in-water emulsions and encapsulate cold press orange peel essential oil by spray drying. Fine comparison of the antigenic compounds in both materials against polyclonal rabbit antibodies, showed that the carbohydrate-rich components with slow mobility of mesquite gum are closely related to the faster ones of gum arabic. Also, close identity was observed for the components in the proteic fraction of both gums. Similar tannin concentrations were found in both materials (approximately 0.43%) with only dark coloured samples bearing higher amounts (approximately 1.9%). Gum arabic retained nearly 100% of the quantity of orange peel essential oil emulsified in water before spray drying, while mesquite gum did so for 90.6% of the citrus oil. From these results it is believed that mesquite gum might be a suitable replacement of gum arabic in arid regions of the world were Prosopis trees have widespread occurrence.

High-molecular weight IGF-2 expression in a haemangiopericytoma associated with hypoglycaemia

Spontaneous hypoglycaemia is usually caused by an insulin-producing islet-cell tumour of the pancreas. Rarely, it can be caused by non-islet cell tumours. Most of the tumours are of mesenchymal type, large, and slowly growing. One representative is haemangiopericytoma (HAP). The present report describes a case of a large recurrent retroperitoneal HAP associated with severe hypoglycaemia. Blood serum insulin and proinsulin concentrations were low. By means of acid-gel chromatography and dot-blot techniques, an increased amount of a high-molecular-weight IGF-2 peptide was found. By using antigen retrieval procedures, IGF-2-immunoreactive tumour cells were found in specimens of the recent tumour recurrence-but not in the original. When the in situ hybridization technique was used it could be shown that IGF-2 mRNA labelling had already occurred in the original tumour specimen, 11 years before the onset of hypoglycaemic symptoms. These observations confirm the hypothesized hypoglycaemic effects of high-molecular-weight (HMW) IGF-2, but also point to the presence of a prolonged compensation of this effect. A literature review, based on 17 similar cases of haemangiopericytoma with hypoglycaemia, is presented. Our observation and findings in the literature review support the idea that non-islet-cell tumour hypoglycaemia is caused by an overproduction of a HMW IGF-2 peptide. The insulin-like effect is mediated via non-specific binding to the insulin receptors. To anticipate patients at risk of developing this kind of hypoglycaemia, the histopathological investigation should include not only immunohistochemical analyses of the presence of IGF-2 peptide, but also in situ hybridization of the IGF-2 mRNA expression.

Hydrophobic interactions between gliadin and proteins and celiac disease

Gliadin-protein interaction and its relationship to the pathogenesis hypotheses of celiac disease was investigated. Wheat germ agglutinin was not immunodetected in gliadin preparations. Peptic-tryptic gliadin digest was used to study the gliadin-protein interactions by crossed immunoelectrophoresis and affinity blotting. Biotinylated gliadin digest interacted with IgG and bovine serum albumin but not with several glycoproteins. Since albumin and IgG light chains are not glycosylated, this interaction is not lectin-like, neither completely immunological because of recognition of the IgG Fc fraction. Immobilized and boiled IgG was not recognized by gliadin digest as a lectin. Gliadin digest fractions from T-gel chromatography reduced the fluorescence intensity of cis-parinaric acid bound to albumin. The gliadin-protein interaction is not lectin-like or completely immunological but hydrophobic. Hydrophobicity of gliadins may contribute to the pathogenic events that result in celiac disease.

Expression of brain nitric oxide synthase in the developing rat pineal gland coincides with the appearance of the adrenergic cyclic guanosine 3',5'-monophosphate response

In the developing rat pineal gland, norepinephrine (NE)-stimulated cyclic guanosine 3',5'-monophosphate (cGMP) formation appears 2 weeks later than that of cyclic adenosine 3',5'-monophosphate (cAMP) formation. Since NE-stimulated cGMP formation requires formation of nitric oxide (NO) in the adult rat pineal, we investigated the developmental appearance of the NO-forming enzyme brain NO-synthase (NOS) to find out whether the delayed cGMP response results from the late appearance of NOS. In this study, we investigated pineal glands of rats aged 8-21 days and 8 weeks. Western blot analysis revealed that NOS-immunoreactivity (NOS-IR) was barely detectable until day 12. On day 15 NOS-IR exhibited the same intensity as in adult rats. Expression of NOS at this postnatal stage appears to be responsible for the developmental appearance of the adrenergic cGMP response.

Multilayer peroxidase-labeled antibody method: comparison with labeled streptavidin-biotin method, avidin-biotin-peroxidase complex method, and peroxidase-antiperoxidase method

A new, extremely sensitive, "multilayer peroxidase-labeled antibody method" is introduced. This method utilizes peroxidase-labeled antibodies that immuno-react with their antigen, but also can be an antigen to other peroxidase-labeled antibodies. An example of this method is: use rabbit IgG as the first antibody, peroxidase-labeled goat antirabbit IgG as the second antibody, peroxidase-labeled rabbit antigoat IgG as the third antibody, peroxidase-labeled goat antirabbit IgG as the fourth antibody, and peroxidase-labeled rabbit antigoat IgG as the fifth antibody in succession. We compared the sensitivities of this multilayer peroxidase-labeled antibody method with that of commercially available immuno-peroxidase staining kits, i.e., avidin-biotin-complex method and peroxidase-antiperoxidase method, both by immunostaining and enzyme-linked immunosorbent assay. The generated signal and background in immunostained sections were determined by a computer-assisted image analyzer and by enzyme-linked immunosorbent assay spectrophotometrically. It was found that a maximum signal/background ratio was obtained with those sections reacted with the first four antibodies in succession by the multilayer peroxidase-labeled antibody method, and those reacted with the five antibodies in succession by the multilayer peroxidase-labeled antibody method in the enzyme-linked immunosorbent assay. Thus, the multilayer peroxidase-labeled antibody method is more sensitive than the avidin-biotin-complex method and the peroxidase-antiperoxidase method.

Products of the porcine group C rotavirus NSP3 gene bind specifically to double-stranded RNA and inhibit activation of the interferon-induced protein kinase PKR

The porcine group C rotavirus (Cowden strain) NSP3 protein (the group C equivalent of the group A gene 7 product, formerly called NS34) shares homology with known double-stranded RNA-binding proteins, such as the interferon-induced, double-stranded RNA-dependent protein kinase PKR. A clone of NSP3, expressed both in vitro and in COS-1 cells, led to the synthesis of minor amounts of a product with an M(r) of 45,000 (the expected full-length M(r) of NSP3) and major amounts of products with M(r)s of 38,000 and 8,000. Restriction enzyme digestion analysis prior to expression in vitro and amino-terminal sequence analysis suggest that the products with M(r)s of 38,000 and 8,000 are cleavage products of the protein with an M(r) of 45,000. The full-length protein and the product with an M(r) of 8,000, both of which contain the motif present in double-stranded RNA-binding proteins, bound specifically to double-stranded RNA. The products with M(r)s of 45,000 and 8,000 were also detected in Cowden strain-infected MA104 cells. NSP3 products expressed in COS-1 cells were capable of inhibiting activation of the double-stranded RNA-dependent protein kinase similar to other double-stranded RNA-binding proteins, and NSP3 products expressed in HeLa cells were capable of rescuing the replication of an interferon-sensitive deletion mutant of vaccinia virus.

Immunodetection of the p21-ras products in human normal and preneoplastic tissues and solid tumors: a review

Immunohistochemical detection of p21-ras to identify and characterize preneoplastic or neoplastic lesions in human tissues is reviewed. Information concerning the commercially available antibodies is presented. Antibodies DWP, Ras-10, Y13-259, YA6-172, NCC-001, and NCC-004 are fully documented with respect to their behavior in appropriate specificity tests and appear to be reliable reagents. After reviewing the data we have identified three groups of tissues or organs with respect to positive immunostaining for p21-ras as the significant criterion of malignancy. These three groups comprise (1) tissues for which no definite conclusion could be drawn (colon, lung, bladder, ovary, and neural and odontogenic tissues) despite occasional claims to the contrary, (2) tissues for which conclusions were negative (pancreas and stomach), and (3) tissues for which p21-ras staining positively discriminated malignant from normal tissues (liver, uterus, and salivary gland). Immunohistochemically detectable levels of products from a mutated ras gene could be demonstrated in a fraction of the samples from colon, lung, and bladder carcinomas, as well as in some histologically normal tissues adjacent to a colon carcinoma. The possibility that a higher relative intensity of the immunostaining reaction for p21-ras might discriminate malignant tissues from normal tissues or benign lesions in breast, pancreas, stomach, lung, uterus, or thyroid samples is suggested. Further studies now appear warranted and a strategy is proposed to validate the conclusions reached thus far.

Enhanced sensitivity of immunoblotting with peroxidase-conjugated antibodies using an adsorbed substrate method

Immunoblots probed with immunoglobulin E (IgE)-containing sera from allergic patients are frequently used in allergy research. Current techniques for detection of specific IgE include radiolabeled and enzyme-linked methods. Although radiolabeled methods are very sensitive, many research groups prefer non-radioactive procedures with equal or greater sensitivity. Alkaline phosphatase (AP) and horse radish peroxidase (HRP) are the most frequently used conjugating enzymes for immunoblotting with the former generally recognized as more sensitive. We describe a method of immunoblot detection using HRP-conjugated immunochemicals with sensitivity equal to and for some systems greater than that of AP conjugates. An adsorbed substrate method for developing immunoblots probed with HRP immunochemical conjugates is compared with traditional AP and HRP methods. The adsorbed substrate system, when used to detect IgE binding to allergic proteins, gives high resolution and delineates bands not otherwise seen. The system has advantages of high sensitivity, rapid development and conservation of immunochemicals. Problems of fading, sensitivity to heat and light, and high background can be solved with increased washing, prompt photography and computer scanning.