Priming to intracellular GFP facilitates antibody formation against the surface GPA RBC antigen after GPA × GFP RBC exposure. (A) Schematic of breeding used to produce GPA × GFP mice. (B) Flow cytometric analysis displayed as histograms of B6, GPA, GFP, and GPA × GFP RBCs after staining with anti-GPA antibody. (C) Detection of endogenous GFP expression via flow cytometric analysis of B6, GPA, GFP, and GPA × GFP RBCs. (D) Flow cytometric analysis, displayed as dot plots, of B6, GPA, GFP, and GPA × GFP RBCs stained with anti-GPA antibody. (E) Representative images of GPA × GFP RBCs (magnification ×100; right image shows single cell). (F) Anti-GPA antibody formation examined in PBS-treated, GFP-primed or B6-exposed recipients. (G-H) Anti-GPA IgM (day 5 after transfusion) (G) or IgG (day 14 after transfusion) (H), after GPA, GPA × GFP, or GPA + GFP RBC exposure. Error bars represent mean ± SD. All panels show combined data from experiments reproduced 3 times. ∗ P ≤ .05, ∗∗ P ≤ .01, ∗∗∗ P ≤ .001, ∗∗∗∗ P ≤ .0001. ns, no significance.