HOD-reactive MD4 B cells endocytose the intracellular antigen GFP. (A) Blood smear image showing mouse RBCs and a MD4 B cell. Scale bar, 6 μm. (B) Experimental schematic of MD4 recipients transfused with HOD RBCs, GFP RBCs, HOD × GFP RBCs, or HOD + GFP RBCs. (C) Flow cytometric gating strategy for detecting GFP + MD4 B cells. (D) Percent B-cell endocytosis of GFP after transfusion of each RBC population is shown. Error bars represent mean ± standard deviation (SD). All panels show representative data from experiments reproduced 2 times. ∗ P ≤ .05, ∗∗ P ≤ .01, ∗∗∗ P ≤ .001. FSC, forward scatter; ns, not significant; SSC, side scatter.