Antibodies to SARS-CoV-2 and RBD spike proteins found in saliva of mRNA vaccine recipients

Vaccines are very important in controlling 2019 coronavirus infection (COVID-19). Two highly effective mRNA vaccines are available in the US – mRNA-1273 from Moderna and BNT162b2 from Pfizer / BioNTech. These vaccines receive antibodies to COVID-19 causative virus spike proteins, true respiratory coronavirus 2 syndrome (SARS-CoV-2). These include neutralizing antibodies (NAbs) that are directed against the receptor binding domain (RBD). Serum NAbs are stimulated at lower levels within about a week of the 1st dose of the vaccine, but the antibody titers are strongly stimulated by the second dose of the Pfizer / BioNTech BNT162b2 vaccine at three weeks or the vaccine Moderna mRNA-1273 at four weeks. .

SARS-CoV-2 is mainly transmitted through the nasal passage or oral tract, and affects cells in the respiratory mucosa and, to a lesser extent, in the airway gastrointestinal. While serum NAbs may offer protection against COVID-19, mucosal antibodies are capable of inhibiting or restricting virus buildup through the oral, nasal, and conjunctival pathways. However, it is unclear whether the mRNA vaccines stimulate mucosal immunity.

Antibodies to protein spike and RBD found in salivary samples from health care workers vaccinated with mRNA vaccines

A team of researchers from the US and the Netherlands recently reported that antibodies to the spike protein and RBD are found in salivary samples from health care workers who have been vaccinated with mRNA vaccines. Within 1-2 weeks of receiving the 2nd dose of the vaccine, 37 out of 37 and 8 of 8 who received the Pfizer and Moderna vaccines, respectively, had IgG antibodies against spike proteins in their saliva , and IgA was also detected in large quantities. . These observations may be very important to understand the immunization of SARS-CoV-2 and COVID-19 infection.
Data from the team survey were provided on the bioRxiv* preprint server.

SARS-CoV-2 NAbs present in saliva may be below assay detection levels

The results of the study show that mRNA vaccines stimulate measurable systemic humoral responses in serum samples in addition to IgG and, to a lesser extent, IgA antibodies to the spike protein and the RBD, which are found in the shed. The IgA detection antibody used in the study identifies dimeric IgA with and without the secretory component. SIgA and IgG are the most common antibodies found in saliva.

Local plasma cells in the salivary glands secrete dIgA, which moves around the mucosae by interacting with the polymeric Ig receptor. Approximately 95% of salivary IgA is in the form of SIgA, while IgG found in saliva is mainly derived from plasma through transudation from gingival blood circulation. The total concentrations of IgM in saliva in healthy individuals are 150150 µg / ml for SIgA, 55 µg / ml for IgM, and 1515 µg / ml for IgG. In contrast, serum density is 10001000-fold for IgG and 100100-fold for total IgA. The researchers estimated that the spike protein IgG titers found in saline are ~ 10,000-fold lower than that in serum, while SIgA titers are ~ 1000-fold lower. Accordingly, any SARS-CoV-2 NAbs in saliva are below detection levels in assays.

Future studies should test the ability of other vaccines to stimulate salivary antibodies

A recent study of SARS-CoV-2 infection in rhesus macaques reported that the virus, when suppressed by passively-induced NAbs in the lungs, can reproduce in nasal turbinates. Assessments of vaccine-induced antibodies taken from nasopharyngeal swabs may provide additional information. However, it may not be possible to measure the IgG accumulation in mucosal interstitial filters using swab sampling and extraction.

Future studies should focus on whether other vaccines such as the Johnson & Johnson adenovirus vector and the infectious protein Novavax are also capable of detecting salivary antibodies, and if so, to what extent. Comparing the ability of different vaccines to prevent their spread to their ability to elicit mucosal antibody responses may help to reveal information about the role of mucosal antibodies.

We show here that the mRNA vaccines stimulate not only humoral systemic responses measured in serum samples, but also IgG and, to a lesser extent, IgA antibodies to the protein- S and the RBD available in saliva. ”

* Important message

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical / behavioral practice, or treated as fixed information.