Development and validation of an enzyme immunoassay for detection and quantification of SARS-CoV-2 salivary IgA and IgG

Abstract

Oral fluids offer a non-invasive sampling method for the detection of antibodies. Quantification of IgA and IgG antibodies in saliva allows studies of the mucosal and systemic immune response after natural infection or vaccination. We developed and validated an enzyme immunoassay (EIA) to detect and quantify salivary IgA and IgG antibodies against the prefusion-stabilized form of the SARS-CoV-2 spike protein. Normalization against total antibody isotype was performed to account for specimen differences, such as collection time and sample volume. Saliva samples collected from 187 SARS-CoV-2 confirmed cases enrolled in 2 cohorts and 373 pre-pandemic saliva samples were tested. The sensitivity of both EIAs was high (IgA: 95.5%; IgG: 89.7%) without compromising specificity (IgA: 99%; IgG: 97%). No cross reactivity with seasonal coronaviruses was observed. The limit of detection for SARS-CoV-2 salivary IgA and IgG assays were 1.98 ng/mL and 0.30 ng/mL, respectively. Salivary IgA and IgG antibodies were detected earlier in patients with mild COVID-19 symptoms than in severe cases. However, severe cases showed higher salivary antibody titers than those with a mild infection. Salivary IgA titers quickly decreased after 6 weeks in mild cases but remained detectable until at least week 10 in severe cases. Salivary IgG titers remained high for all patients, regardless of disease severity. In conclusion, EIAs for both IgA and IgG had high specificity and sensitivity for the confirmation of current or recent SARS-CoV-2 infections and evaluation of the IgA and IgG immune response.

Descriptive evaluation of antibody responses to severe acute respiratory coronavirus virus 2 (SARS-CoV-2) infection in plasma and gingival crevicular fluid in a nursing home cohort—Arkansas, June–August 2020

“…GCF was inactivated by γ radiation before processing and tested using a validated ELISA against full-length prefusion-stabilized SARS-CoV-2 spike protein. 18 GCF antibodies were reported as a gingival crevicular ratio, defined as SARS-CoV-2 specific Ig per total Ig (ng/100 μg). GCF was first tested for IgA, with the remaining volume used for IgG testing.…”

Saliva as a potential surrogate for detection of SARS-CoV-2 in the pediatric population and special care patients

“…In a pioneer study, Xu et al (2020) demonstrated that the viral load in the salivary fluid is approximately 90%, representing a potential vehicle for SARS-CoV-2 transmission. Other authors also mention the high expression of salivary IgA and IgG antibodies as a form of ensuring the validity of COVID-19 diagnosis (Costantini et al 2021).…”