HISTOPATHOLOGY OF GERMFREE ANIMALS

In close collaboration with the Department of Germfree Research, WRAIR, Washington, quantitative, histologic, immunocytochemical, autoadiographic, and electrophoretic studies were performed in normal and irradiated germfree and conventional mice. One third of conventional but no germfree mice were killed by 550 r whole body irradiation. Before radiation, germfree mice had fewer immunologically active cells in lymphatic tissue and a lower serum gamma globulin than conventional animals. After radiation, a pronounced immune response developed in the lymph nodes and spleens of all survivors, associated with a rise in serum gamma globulin in the germfree but a drop in the conventional mice. Gamma globulin decreased after low-lethal doses of irradiation in several mammalian species and this was attributed to leakage from radiation-damaged intestine. In germfree mice no such loss occurs which indicates that bacteria rather than radiation alone are responsible for this depletion. The thymus of germfree mice is smaller and produces fewer cells than its conventional counterpart. Thymus morphology and cell turnover thus correlate directly with immunologic activity which is low in germfree and high in conventional mice. After radiation, the thymus and lymphatic tissue of germfree and conventional animals recover equally well. (Author)