Increased sensitivity of C. parvum treated mice to ionizing whole body irradiation

We have investigated whether C. parvum (CP)-induced stimulation of hematopoiesis affects the survival of mice exposed to the whole body irradiation (WBI). C3Hf/Bu mice treated with CP exhibit an increased hematopoietic colony forming activity in their spleens and blood, but not in their bone marrow, as determined by the exogenous spleen colony assay. Also, CP-treated C3Hf/Bu as well as CBA mice show an increase in their endogenous colonies. This increased hematopoietic activity caused by CP treatment did not protect mice from the consequences of the WBI ranging from 650 to 950 rads. In fact, more mice died if they had been treated with CP. A decrease in the number of erythrocytes was more pronounced in mice treated with CP and irradiation than in those given irradiation alone.