Ultrasensitive Enzyme Immunoassay

Concentration of egg white lysozyme in the serum of healthy subjects after oral administration

1. While the egg white lysozyme preparation ER0068 (Neuzym; Eisai, Tokyo, Japan) is widely used clinically, no studies have been performed on its pharmacokinetic properties at clinically relevant doses. In the present study, we used a highly sensitive two-site enzyme immunoassay in order to determine the pharmacokinetic properties of egg white lysozyme after oral administration of two doses within the clinical range, paying particular attention to the effects of food intake. 2. A total of 22 healthy male subjects aged 20-45 years participated in the study. All subjects had been screened for egg white allergy and non-specific lysozyme inhibitors in their serum. Subjects who received 90 mg ER0068 after an overnight fast reached a maximum serum concentration of 1700 pg/mL within 1 h, compared with non-detectable levels in untreated controls. In a second experiment, subjects received 30 and 90 mg ER0068 after an overnight fast and 90 mg in the non-fasted state and exhibited maximum serum levels of 37, 360 and 49 pg/mL, respectively. Egg white lysozyme concentrations in serum returned to undetectable levels after a maximum of 48 h. 3. We conclude that clinically relevant concentrations of egg white lysozyme are absorbed in significant amounts, despite its high molecular weight. However, food intake considerably reduces the amount of enzyme absorbed.

Earlier detection of human immunodeficiency virus type 1 p24 antigen and immunoglobulin G and M antibodies to p17 antigen in seroconversion serum panels by immune complex transfer enzyme immunoassays

For earlier diagnosis of human immunodeficiency virus type 1 (HIV-1) infection, the sensitivities of immune complex transfer enzyme immunoassays for HIV-1 p24 antigen and antibody immunoglobulin G (IgG) to HIV-1 p17 antigen were improved approximately 25- and 90-fold, respectively, over those of the previous immunoassays by performing solid-phase immunoreactions with shaking and increasing the serum sample volumes, and immune complex transfer enzyme immunoassay of antibody IgM to p17 antigen was also performed in the same way as the improved immunoassay of antibody IgG to p17 antigen. By the improved immunoassays, p24 antigen and antibody IgG to p17 antigen were detected earlier in 32 and 53%, respectively, of the HIV-1 seroconversion serum panels tested than before the improvements, and p24 antigen was detected as early as or earlier than HIV-1 RNA by reverse transcriptase-PCR (RT-PCR) in all of the panels tested. In 4 panels out of 19 tested, antibody IgG to p17 antigen or both antibodies IgG and IgM to p17 antigen were detected earlier than p24 antigen and RNA, although the antibody levels declined slightly before their steep increases usually observed after p24 antigen and RNA. Thus, the window period in diagnosis of HIV-1 infection can be shortened by detection of p24 antigen with the improved immunoassay as much as by detection of RNA with RT-PCR and, in some cases, more by detection of antibodies IgG and IgM to p17 antigen with the improved immunoassays than by detections of p24 antigen with the improved immunoassay and RNA with RT-PCR.

Recombinant p51 as antigen in an immune complex transfer enzyme immunoassay of immunoglobulin G antibody to human immunodeficiency virus type 1

An ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) of antibody immunoglobulin G (IgG) to human immunodeficiency virus type 1 (HIV-1) has been developed using recombinant HIV-1 reverse transcriptase (rRT) as antigen. However, some disadvantages were noted in the use of rRT as antigen: rRT was produced only with low efficiency in widely used strains of Escherichia coli using a rather long DNA fragment (3,012 bp) of the whole HIV-1 pol gene, and it was impossible to produce fusion proteins of RT for simple purification, since rRT is a heterodimer of p66 and p51. In this study, recombinant HIV-1 p51 and p66 with Ser-Ser at the N termini (Ser-Ser-rp51 and Ser-Ser-rp66) were produced in E. coli as fusion proteins with maltose binding protein containing a factor Xa site between the two proteins and were purified after digestion with factor Xa. Ser-Ser-rp51 was produced in larger amounts and purified in higher yields with less polymerization than Ser-Ser-rp66. Polymerized Ser-Ser-rp66 tended to be precipitated on mercaptoacetylation for conjugation to beta-D-galactosidase (used as a label) and showed higher nonspecific and lower specific signals in an immune complex transfer enzyme immunoassay of antibody IgG to HIV-1 than Ser-Ser-rp51. The signals for serum samples of HIV-1-seropositive subjects by immune complex transfer enzyme immunoassay of antibody IgG to HIV-1 using Ser-Ser-rp51 as antigen (Y) were well correlated to those obtained using rRT as antigen (X) (log Y = 0.99 log X + 0.23; r = 0.99). Thus, the use of rp51 as antigen was advantageous over that of rp66 and rRT in an immune complex transfer enzyme immunoassay of antibody IgG to HIV-1.

A sandwich enzyme immunoassay for pulmonary surfactant protein D and measurement of its blood levels in drowning victims

A sensitive sandwich enzyme immunoassay for human pulmonary surfactant protein D (SP-D) was developed and used to examine the blood SP-D levels of drowning victims. Human SP-D was purified from amniotic fluid by chromatographic methods, and an antibody against human SP-D was prepared. A polystyrene ball coated with anti-SP-D IgG was incubated with purified human SP-D, and then with anti-SP-D Fab'-peroxidase conjugate. Peroxidase activity bound to the polystyrene ball was assayed by fluorometry using 3-(4-hydroxyphenyl)propionic acid as the hydrogen donor. The detection limit of human SP-D was 5.2 pg per assay tube. Examination of cross-reactions of this sandwich enzyme immunoassay with proteins from other human organs showed it to be highly specific for lung, and Northern blot analysis detected specific SP-D mRNA expression only in lung. The SP-D concentration of normal human serum was 6.4+/-2.7 (mean+/-S.D.) ng ml(-1) (n=20). The recovery rates of 0.52 ng and 5.2 ng SP-D added to 5 microl normal human serum were 93.6+/-2.7% and 93.6+/-6.1%, respectively. Blood SP-D levels of victims from the saltwater drowning group (n=14) revealed higher concentrations (105.8+/-53.7 ng ml(-1)), while freshwater drowning victims (n=12) were estimated to be 74.1+/-43.9 ng ml(-1). The SP-D levels of 15 subjects who died of hemorrhage (n=5), heart failure (n=8), traumatic shock (n=1), and electrocution (n=1) were lower (22.0+/-8.5 ng ml(-1)), and those of asphyxia victims (n=10) were slightly higher (36.2+/-17.1 ng ml(-1)) than those of other causes of death, except for drowning. These results suggest that in drowning victims, SP-D flowed into the systemic circulation by physiological and physical mechanisms, and the differences of blood SP-D levels between saltwater drowning and freshwater drowning victims are presumed to be influenced by the type of agony and/or the length of survival time in water.

Assessment of mucosal immune response in genitourinary tract using urine

A novel method to assess mucosal immune response in the genitourinary mucosa after immunization with a mucosal vaccine has been developed. In this method, secretory IgA antibody is measured by a highly sensitive enzyme immunoassay (immune-complex transfer enzyme immunoassay) using urine as a specimen. The urinary IgA antibody response could be detected by the immune-complex transfer enzyme immunoassay. In contrast, a conventional enzyme immunoassay (enzyme-linked immunosorbent assay (ELISA)) could not detect this response because of its low sensitivity. Because urine samples can be collected easily and nontraumatically, not only from experimental animals but also from humans, both males and females, the present method may be applicable for assessing the protective efficacy of candidates for mucosal vaccines against sexually transmitted microorganisms, such as human immunodeficiency virus. Furthermore, the usefulness of this method for novel mucosal vaccine formulae was shown for a model in which vaccine antigen and Bordetella pertussis adjuvant were adsorbed onto CaCO, and enclosed in enteric coated capsules.

Determination of the bioavailability of intranasal elcatonin in humans: development of a sandwich transfer enzyme immunoassay for elcatonin

A sandwich transfer enzyme immunoassay for elcatonin (ECT) and its usability for the pharmacokinetic study are described. The anti-salmon calcitonin (SCT) antibody was used for the present assay. The assay procedure consisted of the reaction of ECT with 2,4-dinitrophenylbiotinyl anti-SCT IgG and anti-SCT Fab'-beta-D-galactosidase conjugate, trapping onto (anti-2,4-dinitrophenyl bovine serum albumin) IgG-coated polystyrene balls, eluting with epsilonN-2,4-dinitrophenyl-L-lysine and transferring to streptavidin-coated polystyrene balls and fluorometric detection of beta-D-galactosidase activity. The practical detection limit of ECT was 0.15 pg (44 amol)/50 microl of sample and 3 pg/ml as the concentration. The application of this method has enabled us to directly estimate the bioavailability of ECT dosed intranasaly at a therapeutic level (100 IU, 17 microg) for its anti-osteoporotic effect as compared to an intramuscular dose (40 IU, 6.7 microg). The pharmacokinetic parameters of the intranasal ECT (n = 6) thus estimated were as follows: the area underthe serum concentration-time curve (AUC) = 2,570 +/- 1,650 (SD) pg x min/ml, and the maximal concentration (Cmax) = 60 +/- 25 (SD) pg/ml with the maximal time (Tmax) = 17.5 +/- 6.9 (SD) min, when the AUC for the intramuscular ECT (n = 9) = 9,460 +/- 5,870 (SD) pg x min/ml and the Cmax = 165 +/- 79 (SD) pg/ml with the Tmax = 16.1 +/- 4.2 (SD) min.

Immune complex transfer enzyme immunoassay for antibody IgM to HIV-1 p17 antigen

The immune complex transfer enzyme immunoassay for antibody IgM to HIV-1 p17 antigen is described. Serum samples containing antibody IgM to HIV-1 p17 antigen were incubated simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant p17 (rp17) conjugate and rp17-beta-D-galactosidase conjugate, and the immune complex formed comprising the three components was trapped onto colored polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG. Subsequently, the immune complex was transferred to white polystyrene beads coated with monoclonal mouse (antihuman IgM) IgG in the presence of excess of epsilonN-2,4-dinitrophenyl-L-lysine. The signal for antibody IgM to p17 antigen was the fluorescence intensity by fluorometric assay of beta-D-galactosidase activity bound to the white polystyrene beads. The periods of time required for the formation, trapping, and transferring of the immune complex comprising the three components were more than 4 hr, 2 hr, and 3 hr, respectively. The immunoassay developed was shown to be specific by inhibition of transferring the immune complex in the presence of excess of nonspecific IgM but not IgG. Signals for antibody IgM to p17 antigen with serum samples of HIV-1 seroconversion serum panels,--that is, with serum samples in early stages of the infection--tended to be higher than those with serum samples from HIV-1 asymptomatic carriers probably long after the infection and patients with ARC and AIDS. In contrast, signals for antibody IgG to p17 antigen with serum samples of HIV-1 seroconversion serum panels tended to be higher than signals for antibody IgM to p17 antigen but were much lower than signals for antibody IgG to p17 antigen with serum samples from HIV-1 asymptomatic carriers and patients with ARC and AIDS.

Sensitive enzyme immunoassay of antibodies to HIV-1 p17 antigen using indirectly immobilized recombinant p17 for diagnosis of HIV-1 infection

Recombinant p17 (rp17) antigen of HIV-1 and maltose binding protein-rp17 fusion protein (MBP-rp17) were immobilized onto polystyrene beads in different ways: rp17 and MBP-rp17 were immobilized directly onto polystyrene beads by physical adsorption; biotinyl-rp17 and biotinyl-MBP-rp17 were immobilized indirectly onto streptavidin-coated polystyrene beads; and 2,4-dinitrophenyl (DNP)-MBP-rp17 was immobilized indirectly onto (anti-DNP) IgG-coated polystyrene beads. These directly and indirectly immobilized antigens were incubated with urine samples containing antibody IgG to p17 antigen and subsequently with rp17-beta-D-galactosidase conjugate or (anti-human IgG gamma-chain) Fab'-beta-D-galactosidase conjugate. Beta-D-galactosidase activity bound to the polystyrene beads was assayed by fluorometry. When rp17-beta-D-galactosidase conjugate was used, signals (fluorescence intensities for bound beta-D-galactosidase activity) were much higher with the indirectly immobilized antigens than those with the directly immobilized antigens. By experiments using (anti-human IgG gamma-chain)Fab'-beta-D-galactosidase conjugate, the binding of rp17-beta-D-galactosidase conjugate to antibodies against p17 antigen bound to directly immobilized rp17 antigen was shown to be seriously limited as compared with that to antibodies against p17 antigen bound to indirectly immobilized DNP-MBP-rp17. When rp17-beta-D-galactosidase conjugate and serum samples were used, serum interference was much less with indirectly immobilized DNP-MBP-rp17 than with directly immobilized rp17 antigen, and the sensitivity of enzyme immunoassay for antibody IgG to p17 antigen using indirectly immobilized DNP-MBP-rp17 was 1,000- to 3,000-fold higher than that of enzyme immunoassay using directly immobilized rp17 antigen and Western blotting for p17 band. This sensitive enzyme immunoassay indicated positivity in HIV-1 seroconversion serum panels as early as conventional methods for antibodies to HIV-1 and earlier than Western blotting for p17 band.

Development of a highly sensitive and specific two-site enzyme immunoassay for parathyroid hormone (1-34): application to pharmacokinetic study on intranasal parathyroid hormone (1-34) in human

A highly sensitive and specific two-site enzyme immunoassay for parathyroid hormone (1-34) (PTH(1-34)) and its usability for the pharmacokinetic study are described. Plasma samples were incubated simultaneously with 2,4-dinitrophenylated anti-PTH(1-34) IgG and anti-PTH(1-34) Fab'-beta-D-galactosidase conjugate. The immune complex formed of the three components was trapped onto (anti-2,4-dinitrophenyl group) IgG-coated polystyrene balls. beta-D-Galactosidase activity bound to the polystyrene balls was assayed by fluorometry. The practical detection limit of PTH(1-34) was 50 fg (12 amol)/0.05 ml of sample and 1 pg/ml as the concentration and practically no interference occurred by PTH(1-84) and PTH-related protein (1-34) up to 300 pg/ml and 10 ng/ml, respectively. The application of this method has enabled us to directly estimate the bioavailability of PTH(1-34) dosed intranasally at the prescribed level (0.090 mg). The pharmacokinetic parameters of the intranasal PTH(1-34) (n = 4) thus estimated were as follows: the area under the plasma concentration-time curve (AUC) = 20,500+/-15,900(SD) pg.min/ml; the mean residence time (MRT) = 194+/-16.3(SD) min; and the maximal concentration (Cmax) = 98+/-51 (SD) pg/ml with the maximal time (Tmax) = 35.0+/-12.2(SD) min.

A sandwich transfer enzyme immunoassay for salmon calcitonin: determination of the bioavailability of intranasal salmon calcitonin in human

A sandwich transfer enzyme immunoassay for salmon calcitonin (SCT) and its usability for the pharmacokinetic study are described. The assay procedure consisted of the reaction of SCT with 2,4-dinitrophenyl biotinyl anti-SCT IgG and anti-SCT Fab'-beta-galactosidase conjugate, trapping onto (anti-2,4-dinitrophenyl bovine serum albumin) IgG-coated polystyrene balls, eluting with epsilon N-2,4-dinitrophenyl-L-lysine and transferring to streptavidin-coated polystyrene balls and fluorometric detection of beta-D-galactosidase activity. The practical detection limit of SCT was 0.05 pg (15 amol)/50 microliters of sample and 1 pg/ml as the concentration. The application of this method has enabled us to directly estimate the bioavailability of SCT dosed intranasally at the therapeutic level (160 IU, 31 micrograms) for its anti-osteoporotic effect as compared to an intramuscular dose (10 IU, 1.9 micrograms). The pharmacokinetic parameters of the intranasal SCT (n = 6) thus estimated were as follows: the area under the blood concentration-time curve (AUC) 9400 +/- 5400 (SD) pg.h/ml, and the mean residence time (MRT) = 42 +/- 14 (SD) min, when the AUC for the intramuscular SCT (n = 3) = 5600 +/- 2000 (SD) pg.h/ml and the MRT = 39 +/- 19 (SD) min.

More sensitive immune complex transfer enzyme immunoassay for antibody IgG to p17 of HIV-1 with shorter incubation time for immunoreactions and larger volumes of serum samples

In the previous immune complex transfer enzyme immunoassay for antibody IgG to p17 of HIV-1, the immune complex comprising 2,4-dinitrophenyl-bovine serum albumin-recombinant p17 conjugate, anti-p17 IgG, and recombinant p17-beta-D-galactosidase conjugate was trapped onto polystyrene beads coated with (anti-2,4-dinitrophenyl group) IgG by overnight incubation and was transferred to polystyrene beads coated with (antithuman IgG gamma-chain) IgG by 3 hr incubation in the presence of excess of epsilon N-2,4-dinitrophenyl-L-lysine. These processes were made efficient by incubation with shaking and by using solid phases with larger surface areas. In addition, the volume of serum samples used was increased from 10 microliters to 100 microliters. As a result, the sensitivity was improved 20-30-fold and was approximately 100,000-fold higher than that of Western blotting for p17 band, even when both trapping and transferring of the immune complex were performed for only 30 min. Furthermore, testing many samples became easily possible with higher sensitivity using microplates and a fluororeader.

Sensitive enzyme immunoassay for anti-beta-lactoglobulin IgG in serum

A sensitive enzyme immunoassay for anti-beta-lactoglobulin immunoglobulin G (IgG) in serum is described. Serum containing anti-beta-lactoglobulin IgG was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-beta-lactoglobulin conjugate and beta-lactoglobulin-peroxidase conjugate. The complex formed from the three components was trapped onto polystyrene balls coated with anti-2,4-dinitrophenyl group IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with anti-human IgG.gamma-chain IgG. Bound peroxidase activity was determined by fluorometry. This enzyme immunoassay was 100- to 1000-fold more sensitive and more reliable than the enzyme-linked immunosorbent assay (ELISA). Anti-beta-lactoglobulin IgG was detected in 91% of healthy subjects using this method.

Ultrasensitive enzyme immunoassay

Ultrasensitive enzyme immunoassay methods are reviewed not only for antigens but also for antibodies and haptens with emphasis on factors which limit the sensitivity. Ultrasensitive immunoassays can be developed by noncompetitive solid phase assay systems rather than competitive ones for antigens and antibodies. However, no noncompetitive immunoassays have been available for hapten molecules which cannot be bound simultaneously by two different antibody molecules. This has been overcome by developing methods to derivatize haptens with amino groups so that the derivatized haptens may be measured by two-site noncompetitive assays. For ultrasensitive noncompetitive solid phase immunoassays, the nonspecific binding of labeled reactants (background noise) should be minimized. This has been achieved by developing methods to transfer the complex of analytes and labeled reactants from solid phase to solid phase with minimal dissociation of the complex. Thus, the sensitivity for antigens, haptens and antibodies has been markedly improved and some applications have been made.

A sandwich enzyme immunoassay for brain S-100 protein and its forensic application

A sensitive sandwich enzyme immunoassay for identification of brain S-100 protein in blood or bloodstains containing brain tissue is described. A polystyrene ball coated with rabbit anti-S-100 protein IgG was incubated with human S-100 protein, and then with anti-S-100 Fab'-peroxidase conjugate. Peroxidase activity bound to the polystyrene ball was assayed by fluorometry using 3-(4-hydroxyphenyl)propionic acid as the hydrogen donor. The detection limit of human S-100 protein was 0.6 pg (30 amol) per assay tube. The cross-reaction of this sandwich enzyme immunoassay to other organs was approximately 1/100 or less. Antigenic activity of S-100 protein in bloodstains containing brain extracts was detectable after storage for 36 days at room temperature. The ratio of S-100 protein to total protein (ng/mg) in bloodstains when brain tissue was mixed with normal human blood at concentrations of 5-500 mg/ml was approximately 100-fold those of other samples (liver, heart, intestine, and skeletal muscle). These results indicated that bloodstains mixed with brain tissue were clearly distinguishable from others. Thus, in forensic practice, measurement of S-100 protein or the ratio of S-100 protein to total protein is useful to identify blood and bloodstains containing brain tissue.

Shortening of the window period in diagnosis of HIV-1 infection by simultaneous detection of p24 antigen and antibody IgG to p17 and reverse transcriptase in serum with ultrasensitive enzyme immunoassay

Following HIV infection, there is a window period of 6-8 weeks, during which HIV antibodies are not detectable and the infection cannot be diagnosed by methods for detecting HIV antibodies. However, HIV antigens are detectable in the latter part of the window period, although the level of HIV antigens declines as the level of HIV antibodies increases. We developed an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for the simultaneous detection of both p24 antigen of HIV-1 and antibody IgGs to p17 and reverse transcriptase of HIV-1 in a single assay tube and tested 11 HIV-1 seroconversion serum panels and serum samples randomly collected from 79 HIV-1 seropositive subjects and 100 HIV-1 seronegative subjects. The simultaneous detection was shown not only to shorten the window period significantly as compared with conventional methods for HIV-1 antibody detection but also to make possible a reliable diagnosis of HIV-1 infection from the time of seroconversion until late stages of the infection.

A noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for salmon calcitonin: determination of the bioavailability of subcutaneous salmon calcitonin and its correlation with the hypocalcemic activity in rats

A noncompetitive enzyme immunoassay method (hetero-two-site enzyme immunoassay) for salmon calcitonin (SCT) and its usability for the pharmacokinetic study are described. The method in brief proceeds as follows: centrifugal filtration through a polysaccharide membrane to remove plasma proteins, biotinylation, trapping onto an anti-SCT IgG-coated polystyrene ball, acid elution, coupling with affinity-purified anti-SCT Fab'-peroxidase conjugate, final trapping onto streptavidin-coated polystyrene balls, and measurement of peroxidase activity bound to the balls by fluorometry. The practical detection limit of SCT was 0.1 pg (30 amol)/assay and 2 pg/ml as the assay sample's concentration, which was at least fivefold lower than those previously reported by competitive radioimmunoassays. The application of this method has enabled us to 1) directly estimate the bioavailability of SCT dosed subcutaneously at the therapeutic levels (1.2 and 4.7 micrograms/kg) for its antiosteoporotic effect as compared to an intravenous dose (1.2 micrograms/kg) and 2) search for the relationship between blood level and the hypocalcemic activity of SCT. The pharmacokinetic parameters of subcutaneous SCT (1.2 and 4.7 micrograms/kg) thus estimated were as follows: the area under the blood concentration-time curve (AUC) = 89 and 550 pg.hr/ml, and mean residence time (MRT) = 44 and 65 minutes, respectively, when the AUC for an intravenous SCT (1.2 micrograms/kg) = 160 pg.hr/ml and the MRT = 10 minutes.

Simple and more sensitive immune complex transfer enzyme immunoassay for antibody IgG to reverse transcriptase of HIV-1 using microplates, modified polystyrene solid phase and fluororeader

In a previously reported ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for antibody IgG to HIV-1, polystyrene beads in test tubes were handled with tweezers, and bound beta-D-galactosidase activity was measured with a fluorometer. The use of tweezers was causative of false-positivity by carryover, and testing many samples was difficult. Recently, these drawbacks have been minimized using microplates, a fluororeader, and modified polystyrene beads with sticks for easy handling. The modified polystyrene beads were transferred from wells to wells more quickly and easily without tweezers, eliminating false-positivity due to carryover. The fluorescence intensity for bound beta-D-galactosidase activity was quickly measured with a fluororeader. As a result, it became easy to test many samples with high reliability. However, modified polystyrene beads used were handmade, and the sensitivity was lower than the previous assay with test tubes. In the present study, the condition of the immune complex transfer enzyme immunoassay for antibody IgG to reverse transcriptase of HIV-1 was optimized using microplates, a fluororeader, and polystyrene solid phase with stick, which is commercially available. Testing many samples became easy with higher sensitivity.

Ultrasensitive and more specific enzyme immunoassay (immune complex transfer enzyme immunoassay) for p24 antigen of HIV-1 in serum using affinity-purified rabbit anti-p24 Fab' and monoclonal mouse anti-p24 Fab'

Previously, an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for p24 antigen of HIV-1 was developed. The immune complex comprising 2,4-dinitrophenyl-biotinyl-bovine serum albumin-rabbit anti-p24 Fab' conjugate, p24 antigen, and rabbit anti-p24 Fab' -beta-D-galactosidase conjugate was trapped onto polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, was eluted with epsilon N-2, 4-dintrophenyl-L-lysine, and was transferred to polystyrene beads coated with streptavidin. beta-D-Galactosidase activity bound to the streptavidin-coated polystyrene beads was assayed by fluorometry. This assay was highly sensitive. However, bound beta-D-galactosidase activity had to be assayed for a long time (20 h), and the nonspecific signal was observed in 5% serum samples from subjects with low risk of HIV infection. In the present study, the assay time for bound beta-D-galactosidase activity was shortened to 2.5 h by using 2,4-dinitrophenyl-biotinyl-bovine serum albumin-affinity-purified rabbit anti-p24 Fab' conjugate and affinity-purified rabbit anti-p24 Fab' -beta-D-galactosidase conjugate. Furthermore, the nonspecific signal was found to increase with increasing periods of time for storage of serum samples at -20 degrees C, and this increase was prevented without prolongation of the assay time for bound beta-D-galactosidase activity and without loss of the sensitivity by substituting monoclonal mouse anti-p24 Fab'-beta-D-galactosidase conjugate for affinity-purified rabbit anti-p24 Fab'beta-D-galactosidase conjugate.

Earlier diagnosis of HIV-1 infection by simultaneous detection of p24 antigen and antibody IgGs to p17 and reverse transcriptase in serum with enzyme immunoassay

Serum samples of four HIV-1 seroconversion serum panels were subjected in a single assay tube simultaneously to ultrasensitive enzyme immunoassays (immune complex transfer enzyme immunoassays) for p24 antigen of HIV-1 and for antibody IgGs to p17 and reverse transcriptase (RT) of HIV-1. Signals became positive 7-15 days earlier than the detection of antibodies to HIV-1 by conventional methods and remained strongly positive even after levels of p24 antigen declined. Thus the simultaneous detection of p24 antigen and antibody IgGs to p17 and RT made possible both as early a diagnosis of HIV-1 infection as the appearance of p24 antigen in the circulation, shortening "the window period," and as reliable a diagnosis of the infection as that by the detection of antibodies to HIV-1 from the time of seroconversion until late stages of the infection, since the serum level of antibody IgG to RT was high not only in asymptomatic carriers but also in patients with AIDS-related complex and AIDS.

Measurement of human immunodeficiency virus type 1 p24 in serum by an ultrasensitive enzyme immunoassay, the two-site immune complex transfer enzyme immunoassay

Human immunodeficiency virus type 1 (HIV-1) p24 antigen was measured by an ultrasensitive enzyme immunoassay (two-site immune complex transfer enzyme immunoassay). The antigen was reacted simultaneously with 2,4-dinitrophenyl-biotinyl-bovine serum albumin-anti-recombinant p24 (rp24) Fab' conjugate and anti-rp24 Fab'-beta-D-galactosidase conjugate. The complex that was formed, comprising the three components, was transferred from polystyrene beads coated with affinity-purified (anti-2,4-dinitrophenyl group) immunoglobulin G (IgG) to polystyrene beads coated with streptavidin. The detection limit of rp24 was 2.4 fg (0.1 amol) per assay or 0.24 pg/ml with as little as 10 microliters of serum. When sera were treated at low pH, p24 was detected in 34 (68%) of 50 serum samples from asymptomatic carriers, in 25 (86%) of 29 serum samples from patients with advanced HIV-1 infection, and in none of 117 serum samples from HIV-1-seronegative individuals. Levels of p24 in serum were inversely correlated to those of anti-HIV-1 p24 IgG, and the recovery of rp24 added to serum decreased to zero with increasing levels of anti-HIV-1 p24 IgG in serum. This sensitive method may be used as a powerful tool for investigating the disease.

Further simplification of ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for anti-HTLV-I IgG using microplates and fluororeader

In a previously reported ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) for anti-HTLV-I IgG, polystyrene beads were handled with tweezers, and bound beta-D-galactosidase activity was measured with a fluorometer. The use of tweezers was causative of false-positivity by carryover, and testing many samples was difficult. Recently, these drawbacks have been minimized using microplates and a fluororeader. However, tweezers were still required in the initial and final steps. In the present study, the immune complex, comprising 2,4-dinitrophenyl-antigen, anti-HTLV-I IgG, and antigen-beta-D-galactosidase conjugate, was formed in and trapped onto microplate wells coated with (anti-2,4-dinitrophenyl group) IgG. Subsequently, the microplate wells were incubated with epsilon N-2,4-dinitrophenyl-L-lysine and polystyrene beads, modified by attaching to plates through cylindrical bars and coated with (antihuman IgG gamma-chain) IgG, to transfer the immune complex from the microplate wells to the modified polystyrene beads. Alternatively, modified polystyrene beads coated with (anti-2,4-dinitrophenyl group) IgG and microplate wells coated with (antihuman IgG gamma-chain) IgG were substituted for microplate wells coated with (anti-2,4-dinitrophenyl group) IgG and modified polystyrene beads coated with (antihuman IgG gamma-chain) IgG, respectively. The fluorescence intensity for bound beta-D-galactosidase activity was quickly measured with a fluororeader. Thus the modified polystyrene beads were transferred from wells to wells more quickly and easily without tweezers, eliminating false-positivity due to carryover, and it became easy to test many samples with high sensitivity and reliability, although the assay of bound beta-D-galactosidase activity became slightly more time-consuming.

Noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) and measurement of immunoreactive gamma 2-MSH in plasma of healthy subjects

A noncompetitive enzyme immunoassay (hetero-two-site enzyme immunoassay) for gamma 2-melanocyte-stimulating hormone (gamma 2-MSH) was developed. gamma 2-MSH (1-12) was biotinylated, trapped onto an anti-gamma 2-MSH (1-12) IgG-coated polystyrene bead, eluted at pH 1 after washing to eliminate other biotinylated substances, and measured using two streptavidin-coated polystyrene beads and affinity-purified anti-gamma 2-MSH (1-12) Fab'-peroxidase conjugate. The detection limit of gamma 2-MSH (1-12) was 10-30 amol (16-48 fg)/assay and 130-400 fmol (210-630 pg)/L of plasma. There was little or only slight cross reaction with alpha-MSH, beta-MSH, and gamma 1-MSH. By this immunoassay, the concentration and molecular size of immunoreactive gamma 2-MSH in plasma of healthy subjects were examined, and the results were compared with those by competitive enzyme immunoassay. Immunoreactive gamma 2-MSH measured by competitive enzyme immunoassay was a mixture of substances with high molecular weights (100-500 kDa), and its concentration was calculated to be 50-60 pmol/L using gamma 2-MSH (1-12) as standard. Immunoreactive gamma 2-MSH detected by the noncompetitive enzyme immunoassay after removal of high molecular weight substances was not homogeneous and smaller than gamma 2-MSH (1-12), and its concentration was approximately 1 pmol/L. The exact nature of these immunoreactive gamma 2-MSHs remains to be elucidated. gamma 2-MSH (1-12) added to plasma was degraded rapidly, and the concentration of gamma 2-MSH (1-12) was very low, if any, in plasma of healthy subjects.

Conjugation of recombinant reverse transcriptase of HIV-1 to beta-D-galactosidase from Escherichia coli for ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) of anti-HIV-1 IgG

Recombinant reverse transcriptase (RT) of HIV-1 was conjugated to beta-D-galactosidase from Escherichia coli in three different ways. Maleimide groups were introduced into beta-D-galactosidase molecules using N,N'-o-phenylenedimaleimide in the absence (method I) or presence (method II) of N-ethylmaleimide or into beta-D-galactosidase molecules, which had been treated with excess of 4,4'-dithiodipyridine to block thiol groups, using N-succinimidyl-6-maleimidohexanoate (method III). Subsequently, the maleimide groups were reacted with thiol groups introduced into recombinant RT molecules using N-succinimidyl-S-acetylmercaptoacetate. The conjugates were tested by a sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay). The immune complex consisting of 2,4-dinitrophenyl-bovine serum albumin-recombinant RT conjugate, anti-HIV-1 IgG and recombinant RT-beta-D-galactosidase conjugate was captured by polystyrene beads coated with (anti-2,4-dinitrophenyl group) IgG, eluted with N epsilon-2,4-dinitrophenyl-L-lysine and transferred to polystyrene beads with (anti-human IgG gamma chain) IgG. The conjugate prepared by method III, which showed the least polymerization, the least loss of the specific enzyme activity and the lowest nonspecific binding, improved the sensitivity of the enzyme immunoassay for anti-HIV-1 IgG approximately 30-fold compared with RT-horseradish peroxidase conjugate.

Use of microplates and fluororeader for ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) of anti-HTLV-I IgG

Previously, an ultrasensitive solid phase enzyme immunoassay (immune complex transfer enzyme immunoassay) was described to detect low levels of anti-HTLV-I IgG in serum below those detectable by conventional methods. In this method, polystyrene balls as solid phase were transferred from test tube to test tube with tweezers. This was not only tedious but also causative of false-positivity by carryover, unless tips of the tweezers were washed carefully after each transfer of polystyrene balls. Bound enzyme activities for many samples were measured one by one by fluorometry using a spectrofluorophotometer. As a result, the assay of many samples was difficult. In the present study, microplates and a fluororeader were used in place to test tubes and a spectrofluorophotometer. Polystyrene balls were transferred quickly and easily from well to well by placing a microplate upside down on that containing polystyrene balls, and turning the two plates together upside down. Tweezers were not used for transfer of polystyrene balls, minimizing the possibility of false-positivity. Fluorescence intensities of bound enzyme activities for 96 samples were measured within a minute by using a fluororeader. Thus, it became easy to test many samples, although the sensitivity was lowered to some extent.

Detection of antibody IgG to HIV-1 in urine by ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant p24 as antigen for diagnosis of HIV-1 infection

Anti-HIV-1 IgG in urine was detected by an ultrasensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant p24 gag protein (p24) of HIV-1 as antigen and beta-D-galactosidase from Escherichia coli as label. Anti-HIV-1 IgG in urine was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant p24 conjugate and recombinant p24-beta-D-galactosidase conjugate. The complex formed, consisting of the three components, was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine, and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. Bound beta-D-galactosidase activity was assayed by fluorometry. This assay was at least 3,000-fold more sensitive than conventional methods. The lowest signal among 49 asymptomatic carriers was 3.1-fold higher than the highest nonspecific signal among 100 seronegative subjects. The sensitivity and specificity were both 100%. The positivity could be confirmed by preincubation of urine samples with excess of the antigen. Thus, this assay would be a powerful tool for detecting IgG antibody to HIV-1 in urine.

Anti-HTLV-I IgG in urine detected by sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using a synthetic peptide, Cys-env gp46(188-224), as antigen

Antibody IgG to human T-cell leukemia virus type I (HTLV-I) in urine was detected by a sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using a synthetic peptide, Cys-env gp46(188-224), as antigen, the sensitivity and specificity of which were 100 and 98.5%, respectively, using serum samples. Anti-HTLV-I IgG in urine was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-Cys-env gp46(188-224) conjugate and Cys-env gp46(188-224)-beta-D-galactosidase (Escherichia coli) conjugate. The complex formed, consisting of the three components, was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. Finally, bound beta-D-galactosidase activity was assayed by fluorometry. Thirty-one urine samples from seropositive subjects and 100 urine samples from seronegative subjects were tested. The sensitivity and specificity were 87 and 100%, respectively, with unconcentrated urine samples and 94 and 100%, respectively, with approximately 10-fold concentrated urine samples. These results were superior to those by the conventional ELISA and gelatin particle agglutination test.

The hydrophobic repeated domain of the Clostridium cellulovorans cellulose-binding protein (CbpA) has specific interactions with endoglucanases

We overexpressed one of the hydrophobic repeated domains (HBDs) (110 amino acid residues) of the cellulose-binding protein (CbpA) from Clostridium cellulovorans by making a hybrid protein with the Escherichia coli maltose-binding protein (MalE). The HBD was purified to homogeneity, and interactions between the HBD and endoglucanases were analyzed by a novel interaction Western blotting (immunoblotting) method. The HBD had specific interactions with endoglucanases (EngB and EngD) from C. cellulovorans. These results indicated that the HBD was an endoglucanase binding site of CbpA.

Measurement of anti-thyroglobulin IgG in urine of patients with autoimmune thyroid diseases by sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay)

Anti-thyroglobulin IgG in urine of patients with Graves' disease and chronic thyroiditis and healthy subjects was measured by a sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay). Anti-thyroglobulin IgG in dialyzed urine was reacted simultaneously with 2,4-dinitrophenylated thyroglobulin and thyroglobulin-beta-D-galactosidase conjugate. The immune complex formed consisting of the three components was trapped onto polystyrene balls coated with (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine, and transferred onto polystyrene balls coated with (anti-human IgG gamma-chain) IgG. beta-D-Galactosidase activity bound to the last polystyrene balls was assayed by fluorometry. Anti-thyroglobulin IgG was detected in most of the patients, but not in most of the healthy subjects; levels of anti-thyroglobulin IgG in urine of the patients were well correlated to those in serum of the same patients. The measurement of anti-thyroglobulin IgG in urine by the immune complex transfer enzyme immunoassay was suggested to be useful as a diagnostic aid for autoimmune thyroid diseases. The conventional standard ELISA was not sufficiently sensitive for measuring anti-thyroglobulin IgG in urine.

Detection of antibody IgG to HIV-1 in urine by sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant proteins as antigens for diagnosis of HIV-1 infection

For diagnosis of HIV-1 infection, attempts were made to detect anti-HIV-1 IgG in urine by sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay) using recombinant reverse transcriptase (RT) and p17 as antigens. Anti-HIV-1 IgG in urine was reacted simultaneously with 2,4-dinitrophenyl-bovine serum albumin-recombinant protein conjugate and recombinant protein-enzyme conjugate. The enzymes used as labels were horseradish peroxidase for RT and Escherichia coli beta-D-galactosidase for p17. The complex formed, consisting of the three components, was trapped onto polystyrene balls coated with affinity-purified (anti-2,4-dinitrophenyl group) IgG, eluted with epsilon N-2,4-dinitrophenyl-L-lysine and transferred to polystyrene balls coated with affinity-purified (anti-human IgG gamma-chain) IgG. Finally, bound enzyme activity was assayed by fluorometry. Urine samples were collected from 100 seronegative subjects and 70 seropositive subjects. The sensitivity and specificity were both 100% with unconcentrated urine samples. The positivity was confirmed by preincubation of urine samples with excess of the antigens. The positivity and negativity with one of the two antigens could be confirmed with the other antigen. The positivity with low signals could be confirmed by concentration of urine samples. Detection of anti-HIV-1 IgG in urine by the immune complex transfer enzyme immunoassay using different antigens would make diagnosis of HIV-1 infection possible.

Improved measurement of anti-thyroglobulin IgG in urine of patients with autoimmune thyroid diseases by sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay

Previously, antithyroglobulin IgG was assayed in dialyzed urine from patients with autoimmune thyroid diseases by a sensitive enzyme immunoassay (immune complex transfer enzyme immunoassay), and most of the assay results were useful as a diagnostic aid for autoimmune thyroid diseases. However, dialysis of urine was laborious and time-consuming, and some results were less reliable due to low levels of anti-thyroglobulin IgG in urine. This paper describes some improvements of the assay. Useful assay results could be obtained for most of urine samples without dialysis, although some interfering substance(s) was suggested to be present in some urine samples before dialysis. Accurate assay results with no interference could be obtained after gel filtration by only two min centrifugation in place of dialysis. More reliable assay results for urine samples containing low levels of antithyroglobulin IgG were obtained after concentration using a molecular sieve.

A sensitive sandwich enzyme immunoassay for gamma-seminoprotein and its application to sex discrimination of blood and bloodstains

A sensitive sandwich enzyme immunoassay for gamma-seminoprotein (p30, prostate-specific antigen) is described for sex discrimination of blood and bloodstains. A polystyrene ball coated with rabbit anti-gamma-seminoprotein IgG was incubated with gamma-seminoprotein and, after washing, with affinity-purified rabbit anti-gamma-seminoprotein Fab'-horseradish peroxidase conjugate. Peroxidase activity bound to the polystyrene ball was assayed by fluorometry using 3-(4-hydroxyphenyl)propionic acid as hydrogen donor. The detection limit of gamma-seminoprotein was 0.15 pg per assay. Blood levels of gamma-seminoprotein, measured using 1-10 microliters of blood, were at least 3.3-fold higher in male adults than in female adults. The ratio of gamma-seminoprotein in terms of pg to hemoglobin in terms of mg was significantly higher in male adults than in female adults. Thus, the measurement of gamma-seminoprotein or both gamma-seminoprotein and hemoglobin was useful for the discrimination of blood and bloodstains of male and female adults, although with some limitations.

Immunoenzymatic techniques applied to the specific detection of nucleic acids. A review

Numerous enzymatic and chemical methods are now available for the preparation of non-radioactive nucleic acid probes. Labels, such as enzymes, fluorophores, lumiphores can be attached to the nucleic acid probe either by covalent bonds (direct labelling) or by biospecific recognition after hybridization (indirect labelling). The principle of the latter method is based on the use of a hapten-labelled nucleic acid probe which is generally detected by an immunoenzymatic assay. Indirect labelling has several advantages: this procedure uses multienzyme complexes to increase the number of enzyme molecules associated with hybridization and hence provides an increase in detectability; moreover, haptens (biotin, dinitrophenol, acetylaminofluorene analogues, digoxigenin, brominated or sulphonylated pyrimidines) used to label nucleic acid probes are not sensitive to elevated temperatures (42-80 degrees C), extended incubation times (several hours), detergents and organic solvents currently required in hybridization techniques. The application of the immunoenzymatic and related techniques to nucleic acid probing is reviewed, focussing on the strategies of non-radioactive hybridization, hapten-labelling of nucleic acids and methods for the immunodetection of the hybrids.

An experimental system for determining the influence of microgravity on B lymphocyte activation and cell fusion

The influence of microgravity on lymphocyte activation is central to the understanding of immunological function in space. Moreover, the adaptation of groundbased technologies to microgravity conditions presents opportunities for biotechnological applications including high efficiency production of antibody forming hybridomas. Because the emerging technology of microgravity hybridoma generation is dependent upon activation and cultivation of B lymphocytes during flight, we have adapted mitogen-driven B lymphocyte stimulation and culture that allows for the in vitro generation of large numbers of antibody forming cells suitable for cell fusion over a period of 1-2 weeks. We believe that this activation and cultivation system can be flown on near-term space flights to test fundamental hypotheses about mammalian cell activation, cell fusion, metabolism, secretion, growth, and bio-separation.