Flow cytometry gating strategies. (A) Gating strategy for experiments featured in Figs. 1, 2, and 9. (B) Staining of circulatory leukocytes through intravenous injection of anti-CD45 antibody. Example comparison of the relative frequencies of circulatory leukocytes in a PBMC sample and lung sample. (C) Example plots from the experiment in Fig. 1 of the staining of B cells using an o-RBD probe. Comparison of naive (negative control) and two positive, vaccinated lung samples. PBMC, peripheral blood mononuclear cell.