ABSTRACT
Serological assays have been a useful tool for detection of antibodies to SARS-CoV-2 during the COVID-19 pandemic. These assays are used for epidemiology and serosurveillance to monitor the progression of the pandemic, to identify and differentiate individuals who have developed antibodies from natural infection versus vaccine-induced immunity, and to identify potential donors of convalescent plasma for therapeutic purposes. In this chapter, we describe a commercially available bead-based serological assay, the Luminex® xMAP® SARS-CoV-2 Multi-Antigen IgG Assay, that detects and identifies antibodies against three SARS-CoV-2 antigens. In addition to the assay principle and workflow, we describe modifications that may be used to evaluate alternate sample types, antibody isotypes, and potential neutralizing antibody responses.
Subject(s)
COVID-19 , SARS-CoV-2 , Antibodies, Neutralizing , Antibodies, Viral , COVID-19/diagnosis , COVID-19/therapy , Humans , Immunization, Passive , Immunoglobulin G , Pandemics , Sensitivity and Specificity , COVID-19 SerotherapyABSTRACT
Seasonal influenza vaccination elicits a diminished adaptive immune response in the elderly, and the mechanisms of immunosenescence are not fully understood. Using Ig-Seq, we found a marked increase with age in the prevalence of cross-reactive (CR) serum antibodies that recognize both the H1N1 (vaccine-H1) and H3N2 (vaccine-H3) components of an egg-produced split influenza vaccine. CR antibodies accounted for 73% ± 18% of the serum vaccine responses in a cohort of elderly donors, 65% ± 15% in late middle-aged donors, and only 13% ± 5% in persons under 35 years of age. The antibody response to non-HA antigens was boosted by vaccination. Recombinant expression of 19 vaccine-H1+H3 CR serum monoclonal antibodies (s-mAbs) revealed that they predominantly bound to non-HA influenza proteins. A sizable fraction of vaccine-H1+H3 CR s-mAbs recognized with high affinity the sulfated glycans, in particular sulfated type 2 N-acetyllactosamine (Galß1-4GalNAcß), which is found on egg-produced proteins and thus unlikely to contribute to protection against influenza infection in humans. Antibodies against sulfated glycans in egg-produced vaccine had been identified in animals but were not previously characterized in humans. Collectively, our results provide a quantitative basis for how repeated exposure to split influenza vaccine correlates with unintended focusing of serum antibody responses to non-HA antigens that may result in suboptimal immunity against influenza.