The first isoimmune blood group system of rhesus monkeys (Macaca mulatta): the graded Drh system

The simian-type blood group specificity Drh of rhesus monkeys, first described in 1967, has been proved to be the keystone of a rhesus monkey blood group system, holding a position comparable to that of Rho in the Rh-Hr system. Unlike the Rh-Hr system, however, it does not react well by the ficinated red cell technique and it includes a series of antigens giving graded reactions comparable to those of the human A1-A2 subgroups. The antigens of the Drh system appear to be the most strongly immunogenic, and are thus of greatest importance for the experimental use of these animals, such as in transplantation and blood transfusion.