High throughput surface plasmon resonance imaging method for clinical detection of presence and strength of binding of IgM, IgG and IgA antibodies against SARS-CoV-2 during CoViD-19 infection

Abstract

Surface Plasmon Resonance imaging (SPRi) was used to determine the presence and strength of binding of IgG, IgM and IgA against the Receptor Binding Domain (RBD) of SARS-CoV-2 in sera of 102 CoViD-19 and non-CoViD-19 patients. The SPRi assay simultaneously measures the antibody isotype levels and the strength of binding to the RBD of ultimate 384 patient samples in one run. It turns out that during the course of the disease, the IgG levels and strength of binding increased while generally the IgM and IgA levels go down. Recovered patients all show high strength of binding of the IgG type to the RBD protein. The anti-RBD immunoglobulins SPRi assay provides additional insights in the immune status of patients recovering from CoViD-19. This new high throughput method can be applied for the assessment of the quality of the immune reaction of healthy individuals to SARS-CoV-2 and its mutants in vaccination programs. Surface Plasmon Resonance imaging is an unprecedented technology for high throughput screening of antibody profiling of CoViD19 patients. Fingerprinting of isotypes IgM, IgG and IgA can be performed for 384 patients in one run. An affinity maturation effect was shown for patients recovering from CoViD19.

High Titers of Low Affinity Antibodies in COVID-19 Patients Are Associated With Disease Severity

“…The off-rate ( k d ) was determined to rank the binding strength of the polyclonal antibody pools reacting with the respective antigen. A higher k d correlates with a higher equilibrium dissociation constant ( K D ) and therefore a lower affinity ( 21 ). Figure 3 shows increasing k d with increasing disease severity, which was significant for critically ill patients versus mild for RBD and NCP, and critical versus hospitalized as well as mild for S1S2 and S2, suggesting decreased maturation toward antibodies with higher affinity.…”

“…The IgM, IgG, and IgA isotype antibody response to RBD, NCP, S1S2 (full length spike protein), and S2 antigen was determined for the included patient sera as described previously ( 21 ) ( Figure 1A ). Briefly, an SPRi sensor of a specific antigen was prepared; patient sera were spotted unto this sensor in duplicates for 3 min.…”

“…Antibody interaction affinity with SARS-CoV2 antigens was determined as described previously ( 21 ) ( Figure 1B ). Briefly, patient sera were injected under flow to a multiplex-coated SARS-CoV2 antigen sensor, with a 3-min association and 1-min dissociation time.…”

“…This dissociation constant ( k d ) directly correlates to the value of the equilibrium dissociation constant [ K D ; Schasfoort et al. ( 21 )].…”

“…An attractive alternative is surface plasmon resonance imaging (SPRi). In previous studies, we have demonstrated a high-throughput SPRi assay for the quantitative measurement of IgM, IgG, and IgA antibodies and their apparent polyclonal affinity in the sera of COVID-19 patients in one single experiment with a run time of less than 30 min ( 20 , 21 ). This method is ideally suitable for measuring concentrations of antibodies in patients as well as determining their strength of binding.…”