Multiple sclerosis (MS) patient samples were screened for known or novel retroviruses using an ultrasensitive technique, IMx PERT, that detects the presence of reverse transcriptase (RT). This procedure has 10(5)- to 10(7)-fold greater sensitivity than conventional RT assays and is capable of detecting 10 to 50 virions. Moreover, IMx PERT is at least as sensitive as polymerase chain reaction, and requires no previous knowledge of viral nucleotide sequence. The MS specimens analyzed in this study included 136 sera from 79 patients and 128 cerebrospinal fluid samples from 53 patients with relapsing or chronic progressive disease. In addition, peripheral blood mononuclear cells from 19 MS patients were cultured in an attempt to amplify or induce expression of low-copy number or cell-associated retrovirus. No evidence of retrovirus was found in any of the specimens obtained from MS patients.

A paramagnetic microparticle (MP) assay for antibody to hepatitis C virus (anti-HCV) was developed, in which the probe for antibody consisted of synthetic peptides corresponding to HCV capsid and nonstructural c-100 regions, as well as a recombinant protein corresponding to the nonstructural c33c region. Assay performance was evaluated by testing serum from 108 geographically diverse patients with non-A, non-B hepatitis (NANBH). The frequency of anti-HCV reactivity detected with the MP assay and with an enzyme-linked immunosorbent assay (ELISA) for c-100 was 91 and 70 percent, respectively. All c-100 HCV ELISA-reactive specimens also reacted on the MP assay. In addition, anti-HCV seroconversion in three plasma donors was detected one to two blood collection dates earlier by the MP assay than by the c-100 HCV ELISA and at similar blood collection dates by the MP assay and a second-generation anti-HCV ELISA. Serologic responses to the three distinct antigenic regions of HCV in NANBH patients varied: reactivity to all three antigens was most common (49%), reactivity to both capsid and c33c (40%) was next most common, and single-antigen reactivity was rare (4%). MP assay reactivity of 825 volunteer donors was 0.1 percent. These results demonstrate both the utility of additional HCV antigens for an effective anti-HCV screening assay and the application of paramagnetic MP technology to serologic testing for HCV infection.

A new rapid serologic enzyme immunoassay for antibodies to hepatitis C virus (HCV) is described. The assay combines synthetic peptide and recombinant antigens representing putative structural and non structural HCV gene products with paramagnetic microparticle assay (MP assay) technology. Assay readout is based upon an enzymatically generated fluorescent product which is quantified with a novel semi-automated washer/reader instrument system. Assay sensitivity and specificity was determined to be greater than the first generation HCV C-100 EIA using a non-A, non-B hepatitis disease panel, an HCV performance panel, an HCV seroconversion panel, dilutions of HCV reactive sera, and random volunteer blood donor specimens.

Enzyme-linked immunosorbent assays (ELISAs) can be designed to detect either antigens or antibodies. Nearly all ELISA formats require the separation of reactants from the products of the immunoassay. The product of the assay is an immune complex consisting of target ligand, the analyte, and the reporting probe used to detect the complex that is formed. Because it 1s usually necessary to remove excess analyte as well as excess probe before measurements, several separation steps may be desired, if not required. In the early years, during the evolution of radioimmunoassays (RIAs), it was found that, under certain conditions, antibodies or antigens would bind strongly during brief exposures of solutions to plastic surfaces, such as the inner walls of a tube or a well. The amount of target ligand that would bind proved to be well suited for the competitive assays that were being developed then; the convenience that this phenomen provided has spurred the growth of immunoassay systems for 25 years. Although ELISAs have now generally replaced most RIAs, the principles for coating of the solid phases are similar for both.