Administration of dominant RhD peptides through the nasal mucosa prevents immune responses to RhD protein. The production of serum antibodies, detectable by IELAT (A-D) and IAT (E-H), specific for RhD-positive RBC, is inhibited by the nasal administration of RhD peptides p6 (RhD_52-66), p13 (RhD_97-111), p17 (RhD_117-131), and p28 (RhD_177-191) before the immunization of HLA-DR15 transgenic mice with RhD protein. A representative experiment (n = 12) is shown for each peptide. Splenocyte in vitro proliferative responses (I-L) to purified RhD protein (black bars) above the unstimulated background (white bars) are inhibited when HLA-DR15 transgenic mice are given RhD peptides p6 (RhD_52-66), p13 (RhD_97-111), p17 (RhD_117-131), or p28 (RhD_177-191) intranasally before RhD immunization. Significant differences are shown (Student t test). Error bars indicate SD of triplicates.