Comparative study of a new commercial recombinant line assay and two immunoassays for detection of SARS-CoV-2 IgG antibodies in PCR-confirmed outpatients

ObjectivesCommercially available immunoassays have been developed for detection of antibodies against SARS-CoV-2. However, equivocal and discrepant results between different immunoassay can occur requiring further assessment by confirmatory tests.MethodsWe investigated the new commercial line assay recomLine SARS-CoV-2 IgG (Mikrogen, containing the antigens S1, receptor-binding domain of the spike protein, and nucleocapsid protein (NP) of SARS-CoV-2) within a collection of well characterized serum samples from COVID-19 outpatients (n=49) and SARS-CoV-2-PCR-positive asymptomatic contact persons (n=6) in comparison to two commercial immunoassays, the S1 antigen based Anti-SARS-CoV-2-ELISA IgG by Euroimmun and the NP based Elecsys® Anti-SARS-CoV-2 by Roche.ResultsThe recomLine assay was positive in all samples which had an equivocal or positive result for SARS-CoV-2 antibodies in at least one of the two immunoassays. It showed high agreement with the overall results of the immunoassays (94.5% [Cohen’s kappa = 0.85] and 92.7% [Cohen’s kappa 0.81] to the ELISA by Euroimmun and the assay by Roche, respectively). In addition, high agreement of the reactivity to the specific antigens S1 and NP in the recomLine assays compared to the results of the S1 based ELISA and NP based Elecsys® assay, was found (90.9% [Cohen’s kappa 0.78] and 96.4% [Cohen’s kappa 0.91] for S1 and NP, respectively).ConclusionsThe new recomLine SARS-CoV-2 IgG assay may be used as an additional tool for investigation of equivocal or discrepant results of Anti-SARS-CoV-2 immunoassays and for antigen-specific detection of SARS-CoV-2 IgG antibodies.

Seroreactivity to and Avidity for Recombinant Antigens in Toxoplasmosis

ABSTRACT To improve serodiagnostic methods for the diagnosis of acute toxoplasmosis during pregnancy, a new test system has been developed and evaluated based on the use of recombinant antigens. Five recombinant Toxoplasma gondii antigens (ROP1, MAG1, SAG1, GRA7, and GRA8) were cloned in Escherichia coli, purified, and applied directly onto nitrocellulose membranes in a line assay (recomLine Toxoplasma). A panel of 102 sera from 25 pregnant women with supposed recent toxoplasmosis and from two symptomatic children was compared to a panel of 71 sera from individuals with past infection. Both panels were analyzed using a recombinant line assay for immunoglobulin G (IgG), IgM, and IgA antibodies and a reference enzyme-linked immunosorbent assay. Within the IgM-positive samples, antibodies against ROP1 were predominant regardless of the infection state. In IgG analysis a characteristic antibody pattern was found for very recent infections. This pattern changed to a different one during the time course of infection: antibodies against GRA7 and GRA8 were characteristic for very early IgG, whereas antibodies against SAG1 and MAG1 appeared significantly later. These results were further confirmed by determination of the IgG antibody avidity for every single recombinant antigen. In the time course of infection, IgG antibodies against the early recognized antigens matured significantly earlier than those directed against the later antigens did. The IgA patterns did not give reliable information about the infection time points. The data revealed that the recombinant line assay provides valuable information on the actual state of infection, especially during the early infection time points.

RFLP mapping of a gene for hairy leaf sheath using a recombinant line from Hordeum vulgare L. ×Hordeum bulbosum L. cross

A gene conditioning hairy leaf sheath character, which was derived from Hordeum bulbosum and designated Hsb, was mapped using a cross between Hordeum vulgare and a H. vulgare/H. bulbosum recombinant line. The Hsb locus was tagged relative to eight RFLP markers detecting three loci on the distal part of chromosome 4HL. The map position suggests that Hsb of H. bulbosum is homoeologous to the gene Hp1 of rye (Secale cereale), which pleiotropically governs the traits hairy leaf sheath and hairy peduncle. It is proposed that the recombination break point between H. vulgare and H. bulbosum chromosomes occured at a position homoeologous compared with the 4L/5L translocation in Triticeae genomes, and may reflect a hot spot for chromosome breakage.Key words: Hordeum vulgare, Hordeum bulbosum, comparative mapping, hairy leaf sheath, RFLP.

Pathogenicity of Leptosphaeria maculans Isolates on a Brassica napus-B. juncea Recombinant Line

The Brassica napus-B. juncea recombinant line (MX), resistant to Leptosphaeria maculans, was produced by interspecific crosses and bears one gene (Jlm1) from the B. juncea B genome. We investigated whether this new resistance was race specific by characterizing protection against a large sample of L. maculans isolates. The pathogenicity of 119 isolates of L. maculans comprising 105 A-group isolates and 14 B-group isolates was studied at the cotyledon stage under controlled conditions using the MX line, the susceptible B. napus cultivar Westar, and the resistant B. juncea cultivar Picra. All but one of the isolates were pathogenic on ‘Westar’. Only 3 of the 105 A-group isolates caused very mild symptoms on ‘Picra’. Two of these strains were isolated from the MX line and the other from Sinapis arvensis. The other 102 strains caused hypersensitive-type responses. Most B-group isolates were pathogenic on ‘Picra’. There were differences in pathogenicity among A-group isolates tested on the MX line, whereas all B-group isolates were pathogenic on this line. A-group isolates obtained from the MX line were more frequently pathogenic on the MX line than those obtained from B. napus cultivars. One isolate from S. arvensis infected the MX line. These results suggest that the resistance of the MX line is unlikely to be durable. Thus, the new resistance gene Jlm1 should probably be used in association with other sources of resistance, in plant breeding schemes, to prevent the breakdown of this resistance.