MZ B cells play a role in anti-HOD alloantibody formation. (A-B) Gating strategy (A) and quantification (B) of the percentage of B220⁺CD23⁻CD21^hi MZ B cells in splenocytes obtained from MZ-KO and CD19^+/+ × Notch2^flx/flx (MZ-KO Ctrl) mice. (C-D) Representative line graph (C) and quantification (D) of anti-HOD IgM alloantibody formation in MZ B-cell–KO mice (blue) compared with MZ B-cell–KO littermate control mice (red) following HOD RBC transfusion. (E-F) Representative line graph (E) and quantification (F) of anti-HOD IgG alloantibody formation in MZ B-cell–KO mice (blue) compared with MZ B-cell–KO littermate control mice (red) following HOD RBC transfusion.