Reaction of Human Monoclonal Antibodies to SARS-CoV-2 Proteins With Tissue Antigens: Implications for Autoimmune Diseases

Abstract

We sought to determine whether immune reactivity occurs between anti-SARS-CoV-2 protein antibodies and human tissue antigens, and whether molecular mimicry between COVID-19 viral proteins and human tissues could be the cause. We applied both human monoclonal anti-SARS-Cov-2 antibodies (spike protein, nucleoprotein) and rabbit polyclonal anti-SARS-Cov-2 antibodies (envelope protein, membrane protein) to 55 different tissue antigens. We found that SARS-CoV-2 antibodies had reactions with 28 out of 55 tissue antigens, representing a diversity of tissue groups that included barrier proteins, gastrointestinal, thyroid and neural tissues, and more. We also did selective epitope mapping using BLAST and showed similarities and homology between spike, nucleoprotein, and many other SARS-CoV-2 proteins with the human tissue antigens mitochondria M2, F-actin and TPO. This extensive immune cross-reactivity between SARS-CoV-2 antibodies and different antigen groups may play a role in the multi-system disease process of COVID-19, influence the severity of the disease, precipitate the onset of autoimmunity in susceptible subgroups, and potentially exacerbate autoimmunity in subjects that have pre-existing autoimmune diseases. Very recently, human monoclonal antibodies were approved for use on patients with COVID-19. The human monoclonal antibodies used in this study are almost identical with these approved antibodies. Thus, our results can establish the potential risk for autoimmunity and multi-system disorders with COVID-19 that may come from cross-reactivity between our own human tissues and this dreaded virus, and thus ensure that the badly-needed vaccines and treatments being developed for it are truly safe to use against this disease.

Keywords: COVID-19; SARS-CoV-2; autoimmunity; cross-reactivity; molecular mimicry.

Figure 1

Reaction of anti-SARS-CoV-2 spike protein human monoclonal antibody with human tissue antigens. Each bar represents the calculated mean out of four different values for the same antigen. The mean OD of the anti-SARS-Cov-2 spike protein antibody’s reactivity with the non-reactive 27 tissue antigens +3SD was 0.34, which was used as the cutoff point, represented by the red line. Everything above this cutoff point is significant.

Figure 2

Reaction of anti-SARS-CoV-2 nucleoprotein human monoclonal antibody with human tissue antigens. Each bar represents the calculated mean out of 4 different values for the same antigen. The mean OD of the anti-SARS-Cov-2 nucleoprotein antibody’s reactivity with the non-reactive 31 tissue antigens +3SD was 0.36, which was used as the cutoff point, represented by the red line. Everything above this cutoff point is significant.

Figure 3

Reaction of anti-SARS-CoV-2 envelope protein rabbit polyclonal antibody with human tissue antigens. Each bar represents the calculated mean out of 4 different values for the same antigen. The mean OD of the anti-SARS-Cov-2 envelope protein antibody’s reactivity with the non-reactive 47 tissue antigens +3SD was 0.30, which was used as the cutoff point, represented by the red line. Everything above this cutoff point is significant.

Figure 4

Reaction of anti-SARS-CoV-2 membrane protein rabbit polyclonal antibody with human tissue antigens. Each bar represents the calculated mean out of 4 different values for the same antigen. The mean OD of the anti-SARS-Cov-2 membrane protein antibody’s reactivity with the non-reactive 37 tissue antigens +3SD was 0.32, which was used as the cutoff point, represented by the red line. Everything above this cutoff point is significant.

Figure 5

Demonstration of analytical specificity by dilution study. (A) Shown are the reactions of various dilutions of human monoclonal anti-SARS-CoV-2 spike protein antibody with spike protein (blue diamond ♦), M2 (red square ■), MBP (green triangle ▲), NFP (purple diamond ♦), and GAD-65 (light blue circle ●). (B) Shown are the reactions of various dilutions of human monoclonal anti-SARS-CoV-2 nucleoprotein antibody with nucleoprotein (blue diamond ♦), M2 (red square ■), MBP (green triangle ▲), insulin-R (purple diamond ♦), and GAD-65 (light blue circle ●). (C) Shown are the reactions of various dilutions of rabbit polyclonal anti-SARS-CoV-2 envelope protein antibody with envelope protein (blue diamond ♦), M2 (red square ■), MBP (green triangle ▲), actin (purple diamond ♦), and intestinal epithelial cell (light blue circle ●). (D) Shown are the reactions of various dilutions of rabbit polyclonal anti-SARS-CoV-2 membrane protein antibody with membrane protein (blue diamond ♦), M2 (red square ■), NFP (green triangle ▲), TPO (purple diamond ♦), and intestinal epithelial cell (light blue circle ●).

Figure 6

Demonstration of analytical specificity by inhibition study. (A) Graph shows the inhibition of human monoclonal anti-SARS-CoV-2 spike protein antibody reaction with plates coated with NFP (red square ■), M2 (green triangle ▲), GAD-65 (purple diamond ♦), and MBP (light blue circle ●) with different concentrations of the same antigen in liquid phase. (B) Graph shows the inhibition of human monoclonal anti-SARS-CoV-2 nucleoprotein antibody reaction with plates coated with insulin-R (red square ■), M2 (green triangle ▲), GAD-65 (purple diamond ♦), and MBP (light blue circle ●) with different concentrations of the same antigen in liquid phase. (C) Graph shows the inhibition of rabbit polyclonal anti-SARS-CoV-2 envelope protein antibody reaction with plates coated with intestinal epithelial cell (red square ■), M2 (green triangle ▲), actin (purple diamond ♦), and MBP (light blue circle ●) with different concentrations of the same antigen in liquid phase. (D) Graph shows the inhibition of rabbit polyclonal anti-SARS-CoV-2 membrane protein antibody reaction with plates coated with M2 (red square ■), NFP (green triangle ▲), intestinal epithelial cell (purple diamond ♦), and TPO (light blue circle ●) with different concentrations of the same antigen in liquid phase.

Figure 7

Possible relationship between SARS-CoV-2 proteins and autoimmune target proteins. The cross-reactive patterns between SARS-CoV-2 proteins and autoimmune target proteins may play a role in the systemic inflammatory response from COVID-19, lead to the development of autoimmune diseases post-infection in susceptible subgroups, or potentially play a role in the severity of COVID-19 illness.