Background Considering the course of the current SARS CoV 2 pandemic, it is important to have serological tests for the detection of the anti-SARS CoV-2 humoral immune response for monitoring and prognosis the different stages of the disease. Purpose Herein we describe a novel bridge enzyme-linked immunosorbent assay (b-ELISA) for SARS-CoV-2 antibodies detection in human and other species, employing recombinant Spike protein as a unique antigen, which is produced at high scale in insect larvae. Results Eighty two human control sera/plasmas and 169 COVID-19 patients’ sera/plasmas, confirmed by rRT-PCR, were analysed by the b-ELISA assay. Out of the 169 patient samples, 129 were positive for IgG anti-SARS-CoV-2 and 40 were negative when they were tested by ELISA COVIDAR® IgG. When a cut-off value of 5.0 SDs was established, 124 out of the 129 COVID-19 positive samples were also positive by our developed b-ELISA (sensitivity: 96.12%). A total of 27 animal sera (5 horses, 13 rats, 2 cats and 7 dogs) were employed in order to evaluate the b-ELISA in other animal species. Conclusion The obtained results demonstrate that the method developed herein is versatile, as it is able to detect antibodies anti-SARS-CoV-2 in different animal species without the need to perform and optimize a new assay for each species.

The combined presence of autoantibodies to the 65 kD isoform of glutamic acid decarboxylase (GADA) and to the islet-specific cation efflux transporter ZnT8 (ZnT8A) in serum is the best predictive sign of the loss of immune tolerance and the clinical manifestation of autoimmune diabetes mellitus (DM). The screening of GADA and ZnT8A could be an appropriate alternative to identify diabetic subjects with underlying autoimmunity, helping to reach to a correct diagnosis and guaranteeing the start of an early and adequate treatment. Herein, we describe the expression of a chimera molecule including immunodominant regions of the antigens ZnT8 and GAD65 by using the baculovirus-insect cells system, yielding 30 mg/L culture medium. This recombinant chimera retains the immunoreactive conformation of the epitopes that are recognized by their specific antibodies, so it was used for the development of a high sensitivity (75.51 %) and specificity (98.04 %) bridge ELISA for the detection of highly prevalence ZnT8A and/or GADA, in a one-step screening assay. This immunoassay is useful either to confirm autoimmune diabetes or for detection in routine screening of individuals at risk of autoimmune DM. As DM is a slow progress disease, remaining asymptomatic for a long preclinical period, serological testing is of importance to establish a preventive treatment.

Serology testing for COVID-19 is important in evaluating active immune response against SARS-CoV-2, studying the antibody kinetics, and monitoring reinfections with genetic variants and new virus strains, in particular, the duration of antibodies in virus-exposed individuals and vaccine-mediated immunity. In this work, recombinant S protein of SARS-CoV-2 was expressed in Rachiplusia nu, an important agronomic plague. One gram of insect larvae produces an amount of S protein sufficient for 150 determinations in the ELISA method herein developed. We established a rapid production process for SARS-CoV-2 S protein that showed immunoreactivity for anti-SARS-CoV-2 antibodies and was used as a single antigen for developing the ELISA method with high sensitivity (96.2%) and specificity (98.8%). Our findings provide an efficient and cost-effective platform for large-scale S protein production, and the scale-up is linear, thus avoiding the use of complex equipment like bioreactors.