Immunosuppression by compounds which complex with deoxyribonucleic acid

Compounds selected for their ability to bind to DNA, as measured by the displacement of methyl green from its DNA complex, were tested for immunosuppressive activity in the graft vs. host reaction (GVHR). Seven compounds of the nineteen compounds tested showed significant immunosuppressive activity. Oral administration of the compounds was less effective than intraperitoneal injection in suppressing the GVHR. None of the compounds was immunosuppressive when humoral antibody response to sheep red blood cells was measured. There was good correlation between the ability to suppress the GVHR in vivo and the ability to bind to DNA as measured by methyl green displacement in vitro. However, this does not prove that the immunosuppressive mode of action of the compounds depended on binding to nucleic acid in vivo.