SARS-CoV-2 Exposure Elicits a Strong Mucosal Antibody Response That May Facilitate Quicker Mucosal Viral Clearance

The entry of SARS-CoV-2 via the mucosal surfaces of the upper respiratory tract, including the oral cavity, may be influenced by innate and adaptive immunity. We aimed to determine whether antibodies in secretions might influence the SARS-CoV-2 burden and thus the severity of infection. Blood and stimulated oral fluid (SOF) samples were collected at recruitment (d0) from 173 participants and sequentially at d14, d30 and d90 from 52 participants. Anti-SARS-CoV-2 spike antibodies of the IgG, IgA and SIgA isotypes were detected by ELISA. SARS-CoV-2 RNA copies were quantified by RT-PCR. SARS-CoV-2 RNA copies became negative by d14 in most subjects. At d14, 5/18 SOF samples continued to be RT-PCR-positive. Serum/SOF IgG antibodies were detected in all patients; IgG/IgA/SIgA antibodies increased by d14 and decreased by d90. At d0 and d14, SOF RNA copies were negatively correlated with SOF/serum IgG and with SOF IgA/SIgA antibodies. Higher SOF antibodies were significantly associated with a more rapid decline in SARS-CoV-2 burden. SARS-CoV-2 RNA copies and spike-specific antibodies showed differential trends during the major and minor COVID-19 waves in India. Avidity indices for SOF IgG/IgA antibodies declined by d90. Taken together, our data suggest a potential functional role for SOF anti-SARS-CoV-2 spike antibodies in clearing SARS-CoV-2 from the oral mucosa.