Fig. 2. S100A4 promotes spike protein-specific antibody responses after intranasal immunization with the recombinant spike protein of SARS-CoV-2.

Mice received three intranasal immunizations (i.n.) at an interval of 10 days. For each immunization, mice were intranasally administered with 5 μg spike protein alone or admixed with 10 μg S100A4 or 1 μg cholera toxin (CT). Samples were collected 10 days after the last immunization (a). Levels of anti-spike protein IgG and IgG1 in serum (b) as well as anti-spike protein IgA in broncho-alveolar lavage fluid (BALF) (c), lung exudates (d), nasal lavage (e), and eye exudates (f) were measured by ELISA. Each dot represents measurement from an individual mouse and columns indicate the average values. ^#P = 0.0079 by Mann–Whitney U test. Shown is one of two similar experiments.