MBCs from IM WT prime minimally participate in latter mucosal omicron vaccine boost lung response. (A) Schematic of how transgenic “S1pr2-Cre tdTomato” fate tracking mice tag B cells expressing S1pr2 and are thus within the GC. (B) Vaccination schedule using S1pr2-Cre tdTomato fate tracking mice. Tamoxifen was administered 14 days after prime at time of optimal GC B cell production. Mice were culled 2 wk after boost, with LILN and RILN, respectively, CLN, and lungs collected for analysis. (C) Frequencies of GC B cells (Fas⁺GL7⁺IgD⁻B220⁺) in LILN, RILN, CLN, and lungs as measured by cell staining and flow cytometry. Example flow plots for the gating of GC B cells, and the determination of the frequency of tdTomato⁺ GC B cells is located on the left. (D) For RILN and CLN cells that had measurable frequencies of GC B cells, the proportion of Ad-WT^IM prime-derived (tdTomato⁺) cells (median group response) were indicated in pie charts. (E) Frequencies of o-RBD⁺ B cells (IgD^-B220⁺) in LILN, RILN, and CLN. Example flow plots for the gating of o-RBD⁺ B cells, and the determination of the frequency of tdTomato⁺ GC B cells is located on the left. (F) Proportion of o-RBD⁺ B cells that were Ad-WT^IM prime-derived (tdTomato⁺) cells (median group response). For data in C and E, a one-way ANOVA test with post hoc comparison between all groups was performed. For all data, *P < 0.05 and **P < 0.01. On violin plots, the dashed black line represents the group median and dots represent individual mice. Data are pooled from two independent experiments (n = 3–4 per group per experiment).