Novel and Sensitive Noncompetitive Enzyme Immunoassay (Hetero-Two-Site Enzyme Immunoassay) for Arginine Vasopressin

Recent developments for SPIE-IA, a new sandwich immunoassay format for very small molecules

Recent publications describing new elegant approaches to assay small analytes using noncompetitive format were briefly reviewed. Among these methods, we have developed a new protocol, named SPIE-IA, which involves a cross-linking step achieved using chemical hombifunctional reagents, UV irradiation or free radicals. This new method proved to be useful to detect naturally occurring analyte/antibody complexes or to protect the analytes against degradation by peptidases. On the other hand, SPIE-IA could allow to study the adverse biological effects of UV and some aspects of free radical chemistry or to evaluate the antioxidant activity of molecules.

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.

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.

Radioimmunoassays of arginine vasopressin and atrial natriuretic peptide: application of a common protocol for plasma extraction using Sep-Pak C18 cartridges

A rapid vacuum-driven procedure, using pre-treated Sep-Pak C18 cartridges, has been developed for the simultaneous extraction of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) from plasma. Non-specific interference was removed by fractional elution with an aqueous methanol/trifluoroacetic acid (TFA) mixture. AVP and ANP were coeluted under positive pressure with a methanol/TFA mixture and the eluates air-dried before measurement using separate radioimmunoassays. Assay ranges for AVP and ANP were 0.12-29.5 pmol/L and 0.65-162 pmol/L, respectively, with mean recoveries (standard deviation in parentheses) for AVP of 96.4% (5.5%) at a level of 11.8 pmol/L and for ANP of 94.8% (5.9%) at a level of 32.4 pmol/L. The extraction and assay procedures were validated by observing the changes in plasma AVP and ANP concentrations in normal subjects at different stages of hydration and in elderly patients during treatment for congestive cardiac failure.