Parameters of immunoglobulin extraction from dried blood spot cards and immunoassays for detection of antibody response to pathogens including the novel SARS-CoV-2

Abstract

Dried blood spots (DBS) are routinely used in screening newborns for treatable disorders. Immunoglobulin extraction from DBS, serum or other biological fluids loaded on filter paper cards could represent a valuable method of specimen preservation in monitoring immune response against pathogens as well as vaccination efficiency. In this study using different sources including serum, and monoclonal antibodies we established parameters for antibody extraction from the filter cards to assess antibody reactivity against Helicobacter pylori , measles virus (MV) and the novel coronavirus SARS-CoV-2 antigens. We demonstrated that DBS and dried undiluted serum result in completely preserved antibody activity for immunoassays, including in virus neutralization assays against MV. Extraction efficiency was determined by IgG concentration measurements. The plaque-reduction neutralization titer 50% of dried human serum spots remained stable after more than 10-day storage – 1:359 vs. 1:345 for the corresponding frozen sample. DBSs could be used to monitor immune response to bacterial and viral antigens following natural exposure or immunization. Mice immunized with recombinant spike protein receptor-binding domain of SARS-CoV-2 developed a strong antibody response by day 14 and reached titers above 1:64,000 on day 21 following the secondary boost immunization as measured on DBS samples in antigen-mediated ELISA. Variability in IgG concentration of eluted DBS could be influenced by factors involved in sample application, extraction process and sample characteristics. Adjustment of antibody specific activity to the eluted IgG concentration can increase accuracy of the result interpretation, including in SARS-CoV-2 serological diagnostics.

Evaluation of Dried Blood Spot Testing for SARS-CoV-2 Serology Using a Quantitative Commercial Assay

“…The assay we report does not specifically test for neutralizing antibodies. Some studies have reported potential use of DBS collection for neutralizing antibodies as well [ 50 ]. However, it has been found that high receptor binding domain-specific antibody titers may be indicative of the presence of neutralizing antibodies against SARS-CoV-2 [ 51 , 52 , 53 , 54 ].…”