Rapid increase in salivary IgA and broad recognition of spike protein following SARS-CoV-2 vaccination

Saliva is a key component of mucosal immunity, which protects the oral cavity from viral infections. However, salivary immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), in terms of immunoglobulin dynamics and recognition, have not been investigated sufficiently. In this study, saliva samples were collected from individuals that received SARS-CoV-2 vaccine, and immunoglobulin G (IgG), IgM, and IgA against whole spike protein and S1 protein were measured. IgA against whole spike protein increased significantly following vaccination, while IgA against S1 protein did not. Of note, the IgA response was evident two weeks after the first vaccine dose and continued to rise thereafter. On the contrary, IgG antibodies against S1 increased significantly at four weeks after vaccination. These results reveal the dynamics and recognition antigens of immunoglobulins in saliva, indicating the function of IgA in the mucosal immune system. These findings may pave the way for further studies on mucosal immune response induced by vaccination.