The red cells of rats and mice were tagged in vivo by injection of diisopropylphosphorofluoridate (DFP), labeled with P32, and the disappearance of radioactivity from the circulating red cells was determined. From the data obtained, it is concluded that the disappearance of the red cells is linear with time and that the red cells in both rats and mice have a true life span without measurable random destruction. The life span of the erythrocytes was found to be 60.0 ± 3.2 (S.D.) days in the rat and 40.7 ± 1.9 (S.D.) days in the mouse. Especially in the mouse the determination of the red cell life span with DFP32 is a simple procedure.

In studies on a model of induced pulmonary metastasis in mice a tumour host system was analysed which was not affected by immunogenicity of the tumour for the host; neither intensive immunosuppression nor immunization caused a significant change in the quantity of pulmonary metastatic nodules. In contrast the application of cytostatic drugs and of Corynebacterium parvum could modify the pulmonary resistance to the formation of tumour nodules by a factor greater than 100 in either direction. This finding confirms the observation of others that major modification of the resistance to metastatic tumour formation can occur independently of classical immunological mechanisms. Special attention is drawn to the fact that cyclophosphamide enhances the formation of metastatic nodules in this model by factors of 100 to more than 1,000 whereas other cytostatic drugs including the cyclophosphamide congeners iphosphamide and trophosphamide are active only factors between 2 and 12. The possible practical significance of these findings is discussed.

The distribution and proliferation of CFUs from bone marrow and spleen cell suspensions were followed after injection in lethally irradiated isogeneic mice. It was found that a larger proportion of the injected bone marrow CFUs than of the spleen derived CFUs could be recovered from the recipient's spleen and femur. This consistently higher recovery points to the conclusion that a larger fraction of bone marrow‐derived CFUs than of spleen‐derived CFUs is capable of producing daughter CFUs, most likely due to a commitment to early differentiation of many spleen CFUs.

No abstract

No abstract