Observations on the immunobiology of 'nude' mice.

Mice homozygous for the mutation , which are born without a thymus, accept allogeneic skin grafts. Prior intraperitoneal injection of a thymic cell suspension, or implantation of a thymus on the first day after birth, enables the nude' mice to reject skin grafts. γ-Globulins are generally present in nude' mice. Haemolysin activity in response to sheep red cell injection is detectable but much lower than in normal animals. The similarity of the `nude' syndrome to certain human primary immunological deficiencies is briefly considered in the light of these experiments and of embryological evidence.