Originally presented at the World Microbe Forum
Alexis E. Rose, Adam L. Okerlund, Christopher D. Warner, Christopher J. Detzel
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can infect enterocytes causing increased gut permeability for both viral and bacterial antigens. Antigen translocation leads to local inflammation and increased systemic inflammation.¹⋅²
Viral entry is driven by the binding of the S1 domain of the SARS-CoV-2 spike protein receptor binding domain (RBD) binding to human angiotensin enzyme 2 (ACE2) expressed on host cells. The binding of ACE2 to RBD is necessary for the fusion of the viral envelope with the host cell membrane to deliver viral RNA. Disruption of RBD-ACE2 binding blocks SARS-CoV-2 entry in cells.³
Serum-derived bovine immunoglobulin (SBI) is an oral supplement composed primarily of IgG, IgA and IgM with broad specificity for microbial and viral antigens.
Due to the high homology, 70-80%⁴, between bovine coronavirus and SARS-CoV-2 spike protein epitopes and the prevalence of bovine coronavirus in the USA it is likely SBI contains antibodies that cross react with SARS-CoV-2 spike protein.⁵
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Absorbance increased proportionally to SBI concentration for IgG, IgM and IgA isotypes, demonstrating binding of immunoglobulins to immobilized RBD protein. (Figure 1 A)
Control experiments verified effective blocking and specific binding and detection of SBI IgG, IgM and IgA to RBD protein. (Figure 1 B-C)
SBI treatments reduce binding of ACE2 to RBD proportionally to SBI concentration. Percent inhibition increased from 5.6% to 31.4% for the treatments in Figure 3.
FG negative control treatments did not inhibit ACE2 binding to RBD.
Paired t-test determined SBI and FG treatment groups to be statistically different (p<0.01).
Figure 2 – An RBD-ACE2 binding ELISA was developed to test for the ability of SBI to act as an antagonist. An ACE2 curve was established to verify ELISA performance and to determine assay sensitivity (Panel A). To determine specificity of the detection antibody for rhACE2, the HisProbe-HRP antibody was tested against each ELISA component (Panel B). Error bars represent standard deviation and **** indicates p<.0001.
Figure 3 – SBI inhibits binding of ACE2 and SARS-CoV-2 spike protein. The fish gelatin (FG) control showed no inhibition of ACE2-RBD binding. Error bars represent standard deviation from mean absorbance measurements used to calculate percent inhibition.