Persistence of serum and saliva antibody responses to SARS-CoV-2 spike antigens in COVID-19 patients

Isho, Baweleta; Abe, Kento T.; Zuo, Michelle; Jamal, Alainna J.; Rathod, Bhavisha; Wang, Jenny H.; Li, Zhijie; Chao, Gary; Rojas, Olga L.; Bang, Yeo Myong; Pu, Annie; Christie-Holmes, Natasha; Gervais, Christian; Ceccarelli, Derek; Samavarchi-Tehrani, Payman; Guvenc, Furkan; Budylowski, Patrick; Li, Angel; Paterson, Aimee; Yue, Feng Yun; Marin, Lina M.; Caldwell, Lauren; Wrana, Jeffrey L.; Colwill, Karen; Sicheri, Frank; Mubareka, Samira; Gray-Owen, Scott D.; Drews, Steven J.; Siqueira, Walter L.; Barrios-Rodiles, Miriam; Ostrowski, Mario; Rini, James M.; Durocher, Yves; McGeer, Allison J.; Gommerman, Jennifer L.; Gingras, Anne-Claude

While the antibody response to SARS-CoV-2 has been extensively studied in blood, relatively little is known about the antibody response in saliva and its relationship to systemic antibody levels. Here, we profiled by enzyme-linked immunosorbent assays (ELISAs) IgG, IgA and IgM responses to the SARS-CoV-2 spike protein (full length trimer) and its receptor-binding domain (RBD) in serum and saliva of acute and convalescent patients with laboratory-diagnosed COVID-19 ranging from 3–115 days post-symptom onset (PSO), compared to negative controls. Anti-SARS-CoV-2 antibody responses were readily detected in serum and saliva, with peak IgG levels attained by 16–30 days PSO. Longitudinal analysis revealed that anti-SARS-CoV-2 IgA and IgM antibodies rapidly decayed, while IgG antibodies remained relatively stable up to 105 days PSO in both biofluids. Lastly, IgG, IgM and to a lesser extent IgA responses to spike and RBD in the serum positively correlated with matched saliva samples. This study confirms that serum and saliva IgG antibodies to SARS-CoV-2 are maintained in the majority of COVID-19 patients for at least 3 months PSO. IgG responses in saliva may serve as a surrogate measure of systemic immunity to SARS-CoV-2 based on their correlation with serum IgG responses.