anti-I-Ek antibody (Biotin): The antibody detects: An epitope on mouse I-Ek MHC class II alloantigen The monoclonal antibody 17-3-3 reacts with the I-Ek class II alloantigen on cells from mice of the H-2r haplotype. Reactivity with H-2d and H-2p haplotypes has not been observed.1 Cells from mice of the H-2b, H-2f, H-2g, H-2q, and H-2s haplotypes do not express I-E antigen.