Thymectomy in our hamster colony produced two major changes: (1) wasting disease, and (2) impaired immune response. Wasting occurred in 36 per cent of all males of all ages and was noted even when thymectomy was performed at 4 weeks of age. Lymphoid atrophy was profound and lymphocytopenia sustained. In the non-wasted hamster, the lymphoid atrophy was less striking and there was only transient lymphocytopenia. Experiments in this study were limited to the non-wasted animals. An impaired immune response was demonstrated in both humoral antibody production and in delayed hypersensitivity (heterograft rejection). Male and female hamsters thymectomized at 2 weeks showed an impaired ability to make antibodies against HGG and exhibited prolonged survival of mouse (AJAX) skin. In animals thymectomized at 4 to 8 weeks of age, impaired humoral antibody production could not be demonstrated. Antigen administered on the day of thymectomy was not associated with impaired humoral antibody production. Splenectomy appeared to be more effective than thymectomy in the adult (8-week) hamster in inhibiting humoral antibody production. From these studies, it is evident that the thymectomized, non-wasted male and female hamster has an impaired immune mechanism for both humoral antibody production and heterologous skin rejection.

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