Effect of 6-mercaptopurine on response to major and minor histocompatibility antigens

Pregraft treatment of chicks with 6 mercaptopurine-palladium complex (6-MP-Pd) resulted in a 16% survival of skin allografts incompatible at the major histocompatibility locus B. These incompatible grafts survived beyond 16 weeks postgrafting and showed profuse feather growth. No form of postgraft treatment was necessary. All nontreated incompatible grafts were rejected prior to 4 weeks postgrafting with no evidence of feather development. The same treatment, however, did not significantly suppress rejection of B-system compatible grafts which differed at minor histocompatibility loci. The rate of feather growth in successful B-system compatible grafts was significantly enhanced by the 6-MP-Pd treatment through 2 weeks postgrafting. Though the drug appears to affect the cellular immune system, the humoral immune response was unaffected as evidenced by a high antibody titer following turkey erythrocyte challenge.