RHD and fetal erythroblastosis: Other causes of HDFN include alloantibodies targeting other Rh antigens (such as c, C, E, and e), antigens of the Kell blood group (e.g., anti-K and anti-k), Kidd blood group (e.g., anti-Jka and anti-Jkb), Duffy blood group (e.g., anti-Fya), and MNS and s blood group.